Shifts In IQ Over Time

The chart, via Razib Khan, is based upon polygenetic scores calculated based upon ancient DNA. 

Semi-Recessive Genes

Some genes classified as recessive genes that have their main phenotypical effects only when both copies of it are present, are actually only "semi-recessive" and have much milder versions of the same phenotypic effects in "carriers" with only one copy of the gene.

A new pre-print at bioRxiv demonstrates this by looking at 1929 genes considered recessive in the British UK Biobank database which includes 378,751 unrelated European individuals, singling out carriers of recessive genes associated with intellectual disabilities, who exhibit below average intellectual abilities themselves, as an example.

The abstract explains that:

The genetic landscape of human Mendelian diseases is shaped by mutation and selection. Selection is mediated by phenotypic effects which interfere with health and reproductive success. Although selection on heterozygotes is well-established in autosomal dominant disorders, convincing evidence for selection in carriers of pathogenic variants associated with recessive conditions is limited, with only a few specific cases documented.

We studied heterozygous pathogenic variants in 1,929 genes, which cause recessive diseases when bi-allelic, in a cohort of 378,751 unrelated European individuals from the UK Biobank. We assessed the impact of these pathogenic variants on reproductive success. We find evidence for fitness effects in heterozygous carriers for recessive genes, especially for variants in constrained genes across a broad range of diseases. Our data suggest reproductive effects at the population level, and hence natural selection, for autosomal recessive disease variants. We further show that variants in genes that underlie intellectual disability are associated with reduced cognition measures in carriers. In concordance with this, we observe an altered genetic landscape, characterized by a threefold reduction in the calculated frequency of biallelic intellectual disability in the population relative to other recessive disorders. The existence of phenotypic and selective effects of pathogenic variants in constrained recessive genes is consistent with a gradient of heterozygote effects, rather than a strict dominant-recessive dichotomy.

Hila Fridman, et al., "Reproductive and cognitive effects in carriers of recessive pathogenic variants" bioRxiv (October 1, 2024). https://doi.org/10.1101/2024.09.30.615774

Diet Drives Height

Individual variation in height, like individual variation in IQ, is strongly influenced by genetics. But, population level variations in height (between populations or over time) is profoundly influenced by environment, rather than genetic legacies. There is a good case to be made that the same is true of IQ.

This paradox is also seen, for example, in modern Japan and South Korea where height is closely correlated with year of birth, with children born later in more economically prosperous times with less food scarcity ending up taller.

This also provides a food production counterpart to the "coal curse" by which regions with particularly great coal resources lagged in later economic development as the natural resource based economy fostered by rich coal resources prevented other forms of economic production from thriving, which mattered when coal became less economically important.

In the late nineteenth century, the North American bison was brought to the brink of extinction in just over a decade. We demonstrate that the loss of the bison had immediate, negative consequences for the Native Americans who relied on them and ultimately resulted in a permanent reversal of fortunes. Once amongst the tallest people in the world, the generations of bison-reliant people born after the slaughter lost their entire height advantage. By the early twentieth century, child mortality was 16 percentage points higher and the probability of reporting an occupation 29.7 percentage points lower in bison nations compared to nations that were never reliant on the bison. Throughout the latter half of the twentieth century and into the present, income per capita has remained 28 percent lower, on average, for bison nations. This persistent gap cannot be explained by differences in agricultural productivity, self-governance, or application of the Dawes Act. We provide evidence that this historical shock altered the dynamic path of development for formerly bison-reliant nations. We demonstrate that limited access to credit constrained the ability of bison nations to adjust through re-specialization and migration.

Donn. L. Feir, Rob Gillezeau & Maggie E.C. Jones, "The Slaughter of the Bison and Reversal of Fortunes on the Great Plains" NBER Working Paper 30368 (August 2022), DOI 10.3386/w30368

Troödons

Troödons are currently my favorite dinosaur. But for the extraterrestrial impact that wiped out the dinosaurs in the Gulf of Mexico about 65 million years ago, they would have been top candidates to become the dominant intelligent species on Earth.

A Troödon "is a large-brained nocturnal Troodontid theropod, which lived in the latter part of the Cretaceous period. It . . . may have had camouflage markings on its hide, to help it catch the nocturnal mammals which formed a small part of its diet. . . . it was also feathered. Troodon had abnormally large eyes, and these helped Troodon to see after the setting of the sun . . . . Troodon . . . is generally accepted as having been . . . warm - blooded. . . . It lived in what is now North America during the late Cretaceous Period (100-65 mya) and grew to be about 8 feet to 10 feet long and about 110 lbs. in weight. This slender little dinosaur might be the most intelligent dinosaur ever to exist. Troodon ate mammals, small dinosaurs, eggs and juvenile Hadrosaurs. It also specializes in pack hunting to hunt bigger prey.

From the Dinosaur Wiki. 

Explaining The Genetic Fitness Advantage Of LP and EDAR and Skin Color

In West Eurasia, the strongest target of genetic selective fitness adaptation is lactase persistence (LP) (see also here) which allows adults to drink milk, which surged around the time that Indo-Europeans migrated en masse across Europe in the late Neolithic era and early Bronze Age (often were more herding based food production than the first wave Neolithic populations of Europe derived from Anatolian farmers), and with sometimes regionally distinct genes that have the same effect, upon the arrival of pastoralism in the Near East and Africa.

In East Eurasia and the Americas, the EDAR gene which is responsible for much of the distinctively "East Asian" phenotype is a similarly powerful selective fitness adaptation in the Upper Paleolithic era (roughly speaking, after humans expanded out of Africa and before agriculture was developed). What specifically does it do?

A derived G-allele point mutation (SNP) with pleiotropic effects in EDAR, 370A or rs3827760, found in most modern East Asians and Native Americans but not common in African or European populations, is thought to be one of the key genes responsible for a number of differences between these populations, including the thicker hair, more numerous sweat glands, smaller breasts, and the Sinodont dentition (so-called shovel incisors) characteristic of East Asians. This mutation is also implicated in ear morphology differences and reduced chin protrusion. 

The mutation arose in humans approximately 30,000 years ago, and now is found in 93% of Han Chinese and in the majority of people in nearby Asian populations. 

It has been hypothesized that natural selection favored this allele during the last ice age in a population of people living in isolation in Beringia, as it may play a role in the synthesis of breast milk under Vitamin D-poor conditions. 

Previous research has shown that both LP and EDAR genes may make it easier for mothers to get Vitamin D and/or to pass Vitamin D to their children during pregnancy and in breast feeding. 

But, what is so great about mothers having high levels of Vitamin D and passing it on to their children?

Well, it turns out that the presence of Vitamin D in a mother during pregnancy enhances the IQ of her children, which has great potential to be fitness enhancing, on top of benefits like preventing miscarriage, enhancing fertility, and having immune system enhancing properties.

The importance of Vitamin D could also explain apparent selective fitness effects of matching skin color appropriately to latitude, i.e. favoring pale skin at high latitudes to enhance Vitamin D levels, while favoring darker skin at lower latitudes where solar exposure is more intense to prevent sun burns and skin cancer where it is possible to get sufficient Vitamin D even with darker skin.

The paper and its abstract are as follows:

Background

Vitamin D is critical to embryonic neuronal differentiation and other developmental processes that may affect future neurocognitive function. However, observational studies have found inconsistent associations between gestational vitamin D and neurocognitive outcomes. 

Objectives

We examined the association of gestational 25-hydroxyvitamin D [25(OH)D] with children's IQ at 4–6 y, and explored whether associations differed by race. 

Methods

This study used data from the CANDLE (Conditions Affecting Neurocognitive Development and Learning in Early Childhood) cohort. Between 2006 and 2011, CANDLE recruited 1503 women in their second trimester of healthy singleton pregnancies. Inclusion criteria for this analysis were gestation of ≥34 wk and availability of 25(OH)D and IQ data. Associations between second-trimester 25(OH)D plasma concentration and Stanford-Binet IQ scores in offspring at 4–6 y were examined using multivariable linear regression; interaction terms were used to explore possible effect modification by race. 

Results

Mean ± SD 25(OH)D concentration among 1019 eligible dyads was 21.6 ± 8.4 ng/mL, measured at a mean ± SD gestational age of 23.0 ± 3.0 wk. Vitamin D deficiency [25(OH)D < 20 ng/mL] was observed in 45.6%. Maternal 25(OH)D differed by race with a mean ± SD of 19.8 ± 7.2 ng/mL in Blacks sand 25.9 ± 9.3 ng/mL in Whites ( P < 0.001). In adjusted models a 10-ng/mL increase in 25(OH)D was associated with a 1.17-point higher Full Scale IQ (95% CI: 0.27, 2.06 points), a 1.17-point higher Verbal IQ (95% CI: 0.19, 2.15 points), and a 1.03-point higher Nonverbal IQ (95% CI: 0.10, 1.95 points). We observed no evidence of effect modification by race. 

Conclusions

Second-trimester maternal 25(OH)D was positively associated with IQ at 4–6 y, suggesting that gestational vitamin D status may be an important predictor of neurocognitive development. These findings may help inform prenatal nutrition recommendations and may be especially relevant for Black and other dark-skinned women at high risk of vitamin D deficiency.

Melissa M Melough, et al., "Maternal Plasma 25-Hydroxyvitamin D during Gestation Is Positively Associated with Neurocognitive Development in Offspring at Age 4–6 Years." The Journal of Nutrition (2020). DOI: 10.1093/jn/nxaa309

Why Are Hyaenas Smart?

Behavioural data indicate that there has been considerable convergence between primates and hyaenas with respect to their social cognitive abilities.

From here (hat tip to Razib Khan).

I have long attributed the exceptional intelligence of hyaenas, one of the most intelligent and successful African megafauna, to the fact that unlike most other mammals, the reproductive organs of hyaenas require both the male and female to be simultaneous aroused to reproduce. This has the effect of giving female hyaenas much more control of their reproductive decisions than comparable felines and canines. 

Hyaenas are the poster children for Planned Parenthood of the animal world.

22,000 Years Of Climate Change And History In One Comic

xkcd has an excellent comic summing up 22,000 years of climate change and the associated pre-historic and historical events taking place along the way in one oversized comic.

Two bits of commentary are in order.

First, xkcd has repeatedly demonstrated that often there is just no good substitute for drawing something to scale, even if that means it won't fit on the confines of an ordinary sized comic, or an ordinary sized piece of paper or book.  This is just such a case.

Second, while the comic is largely spot on when it comes to historical dates, the smoothing in the temperature diagram (which the author, in fairness, acknowledges is present in the comic) comes at the cost of a pretty important feature of the data from the period of about 40,000 to 10,000 years ago, which is that the temperature was wildly unstable and oscillated dramatically over much of that time frame, which is one important reason that farming had trouble establishing itself. It is hard to establish agriculture when one generation one set of crops work, and two generations later, an entirely different climate prevails.

To recap:

The key paleoclimate data are presented in the chart below.

 

Ignoring for the moment their simulated data in light gray bar graph form: 

Estimated dates of some well-studied cases of the initial emergence of cultivation are on the horizontal axis (8, 54, 55). Climate variability (Left) is an indicator of the 100-y maximum difference in surface temperature measured by levels of δ¹⁸O from Greenland ice cores (SI Appendix). A value of 4 on the vertical axis indicates a difference in average temperature over a 100-y period equal to about 5 °C.  

As the chart indicates, intermittent periods of wild temperature variation over the span of just a few generations was the norm for the entire Upper Paleolithic era (about 40,000-50,000 years ago), after which temperatures became much more stable starting at the beginning of the Holocene era about 10,000 years ago when farming first emerged in the Fertile Crescent and China and the middle latitudes of the Americas (farming arose independently at later times in the New Guinea Highlands, Sub-Saharan Africa and the Eastern United States).

This feature is material to the presentation because the big point of the comic is to show how extreme and unprecedented rapid climate change in the present is relative to the past.  And, compared to the last 10,000 years that is correct.  Moreover, there is extremely solid evidence showing that climate change now is man-made, which was not true of climate instability from 40,000 to 10,000 years ago. But, this pretty important detail does make for a more complicated story.

This rapid fluctuation during the last glacial maximum around 20,000 to 22,000 years ago also helps explain while the world experienced an intense population bottleneck at the time even though much of it was not covered with ice.

And, this rapid fluctuation may have been a driver of mass migrations across the globe by Upper Paleolithic populations whose existing habitats became uninhabitable again and again.  This placed Upper Paleolithic modern humans under severe selection pressure for adaptability, which is a trait that it is fair to say distinguished us more from other archaic human populations, like Neanderthals, that did not survive, than straight "IQ".

Did Human Female Pelvis Evolution Create Another Biological Clock?

The obstetrical dilemma hypothesis states that the human female pelvis represents a compromise between designs most suitable for childbirth and bipedal locomotion, respectively. This hypothesis has been challenged recently on biomechanical, metabolic, and biocultural grounds. Here we provide evidence for the pelvis’ developmental adaptation to the problem of birthing large-headed/large-bodied babies. 

We show that the female pelvis reaches its obstetrically most adequate morphology around the time of maximum fertility but later reverts to a mode of development similar to that of males, which significantly reduces the dimensions of the birth canal. These developmental changes are likely mediated by hormonal changes during puberty and menopause, indicating “on-demand” adjustment of pelvic shape to the needs of childbirth.

Via John Hawks.

Everyone know that women can only have children from puberty to menopause, and most people who have lived in the social world of college students know that female fertility declines markedly with age before menopause.  All of this, however, is basically directly hormonal and biochemical, not mechanical and morphological according to hormonal cues.

The new paper suggests that shifts in women's hips over their life cycle provides an independent biological clock that influences fertility and provides a biological bias towards having children in your 20s, rather than your 30s or later.  Of course, medically safe C-sections can now bypass the limits of the birth canal on safe births later in life.  But, this study ought to give pause to women who think that vaginal births for mothers of advanced maternal age are desirable because they are more "natural."

The issue of large-headed/large-bodies babies is a big one because many evolutionary anthropologists see large headed babies as a critical piece of evolution that has facilitated higher IQ in modern humans than in other primates.  And, it is widely accepted that higher IQ is a key factor in modern human selective fitness.

Given the ongoing relevance of IQ and the existence of safe C-sections, is it conceivable that we could evolve to a state where safe vaginal births are no longer possible because selection for high IQ leads to selection for large headed babies and hip size is not longer a meaningful constraint on that tendency?

This paper is also a welcome reminder that genetically driven phenotypes are not necessarily an all or nothing thing.  People's bodies change over their lifespans and our genes are clever enough to adapt one way at one age and another at a later age for maximum selective fitness.

Personalities Aren't Just For Humans

Recent studies show that animals far removed from mammals have recognizable personalities.

There are extroverted and introverted sharks in the same species.  The extroverts scare away threats by hanging out in groups.  The introverts head off alone to isolated places and rely on camouflage.

There are also aggressive and docile female communal spiders, common in the American Southeast.  Different mixes of personality are favored in different locations, with the proportion of each personality, which are hereditary, providing the first solid evidence of group selection.  The personality proportions remain the same, even in places where the radically different mix of aggressive and docile females found in local spiders of the same species would be more adaptive.

Anthropologists have demonstrated fairly convincingly that there are differences at the level of coherent ethnic, regional and national cultures in what would normally be considered to be personality traits, such as differences between cultural norms in Northern China, which was traditionally a wheat and millet farming area relative to Southern China, which was traditionally a rice farming area.  One of the ongoing debates in cultural history, anthropology and genetics is the extent to which a nation's "national character" is purely a product of cultural transmission, or instead involves (at least in part) differences in population genetic make up with group selection favoring different mixes of personalities in different environments that continue to manifest even as migration and cultural change make old the balancing selection that produced the ancestral mix of personalities of a "nation" dysfunctional in a new environment.  (The evidence concerning the wheat v. rice farming dichotomy in China tends to favor a cultural rather than a genetic source, by the way, which is the leading view, for the most part.)

While some seemingly complex phenotypes really do have complex genotypes as their source, other seemingly complex phenotypes can arise from just a single genetic locus (in the reference, butterfly wing patterns).  There are also a variety of candidate simple genes with apparent impacts on personality.  Scientists have similarly identified a very simple single locus that can be used to make fruit flies homosexual or heterosexual.

The relatively discrete personality categories observed in some species, patterns of balancing selection within groups of personality types, and the fact that, for example, the personality distribution of humans with high IQs is quite similar to the personality distribution of other humans, suggests like unlike massively polygenetic traits like IQ or stature with a quite continuous range of values and strong bias towards the fitness enhancing direction, that a fairly modest number of common genetic variants may account for personality differences.

But, large scale comprehensive searches for personality genes in humans have mostly come up empty.  Yet, there is strong evidence that personality has a strong hereditary component from sources like twin studies that strongly suggests that at least some genotype plays a major role in shaping a person's personality.  As recent studies of schizophrenia reveal, one problem with these studies may be insufficiently precise definitions of personality types to capture the link between genotype and phenotype.

* * * *

Not quite on topic, but also fascinating is a newly discovered species of parasitic ant that evolved from the species of ant for which it is a parasite (something confirmed with a genetic analysis), in the very same ant colony.  This is essentially the insect equivalent of vampires evolving as a new parasitic species of humans within a single human community.

Xenolinguistics

Researchers have deciphered a class of words in the language of wild dolphins that make up about half of their conversations.  Specifically, they have learned to identify the names that wild dolphins use for each other (also called "signature whistles"), established that these dolphin whistles, first distinguished in the 1960s, really are names of individual dolphins and learned how these names are used in dolphin conversations.

[D]olphin signature whistles are exclusive to individuals, rather than being part of a shared repertoire. They’re social sounds, unlike bird songs which are largely used to attract mates or defend territories. And they’re learned; many animals like birds and monkeys use distinctive calls to refer to specific objects (like different types of predators), but these are innate and inherited behaviours. “The use of new or learned sounds to label an object or class of objects is rare in the animal kingdom,” says King.

This combination of traits makes the signature whistles unique in the non-human world, at least for now. It’s possible that parrots and other birds might use similar calls. 

Reference: King & Janik. 2013. Bottlenose dolphins can use learned vocal labels to address each other. PNAS http://dx.doi.org/10.1073/pnas.1304459110

The fact that so much of the conversations of dolphins consist of proper names also suggests that while dolphins do have a more human-like language than most other species of animals that their language probably has considerably less lexical content (i.e. fewer words) than even the most primitive human language.  A dictionary of dolphinese would have a huge directory of individuals with only a modest vocabulary beyond that.  The way that the signature whistles are used, however, suggest that there is a fair amount of "grammatical context" to what one means and when one uses one based on context and intended meaning.

Back To Ancient History

The burst of early spring physics conferences seem to be past and so it is time to think about the deep past and population genetics again.

* John Hawks have flagged a number of interesting articles.  One study, linking population size and technological complexity in Oceania at first contact with European sailors reaches a facinating conclusion:

Much human adaptation depends on the gradual accumulation of culturally transmitted knowledge and technology. Recent models of this process predict that large, well-connected populations will have more diverse and complex tool kits than small, isolated populations. While several examples of the loss of technology in small populations are consistent with this prediction, it found no support in two systematic quantitative tests. Both studies were based on data from continental populations in which contact rates were not available, and therefore these studies do not provide a test of the models. Here, we show that in Oceania, around the time of early European contact, islands with small populations had less complicated marine foraging technology. This finding suggests that explanations of existing cultural variation based on optimality models alone are incomplete because demography plays an important role in generating cumulative cultural adaptation. It also indicates that hominin populations with similar cognitive abilities may leave very different archaeological records, a conclusion that has important implications for our understanding of the origin of anatomically modern humans and their evolved psychology.
 

* On the methodology front, someone has found a way to turn W.E.I.R.D. samples into a feature rather than a bug when doing genomics:

Although much is known about college students as a special sample in terms of their behavioral traits such as intelligence and academic motivation, no studies have examined whether college students represent a “biased” sample in terms of their genotype frequencies. The present study investigated this issue by examining the Hardy–Weinberg equilibrium of genotype frequencies of 284 SNPs covering major neurotransmitter genes in a sample of 478 Chinese college students, comparing these frequencies with those of a community sample (the 1000 Genomes dataset), and examining behavioral correlates of the SNPs in Hardy–Weinberg disequilibrium. Results showed that 24 loci showed Hardy–Weinberg disequilibrium among college students, but only two of these were in disequilibrium in the 1000 Genomes sample. These loci were found to be associated with mathematical abilities, executive functions, motivation, and adjustment-related behaviors such as alcohol use and emotion recognition. Generally, genotypes overrepresented in the college sample showed better performance and adjustment than under-represented or non-biased genotypes. This study illustrates a new approach to studying genetic correlates of traits associated with a socially-selected group—college students—and presents the first evidence of genetic stratification in terms of education attainment.
 

* On the "to do" list, one of the projects at the top of list is to look into the circumstances that lead to language formation, which may or may not be distinct from "ordinary" language evolution.  A number of examples and leads to research come to mind to get at it, but full fledged language formation is very rare and mostly prehistoric with the exception of certain creoles and a couple of other outliers.

There are creoles whose formation process is well documented, and short of creoles punctuated language evolution via intense language contact.  There are instances of isolated communities of deaf people developing their own personal sign languages from scratch.  There is a growing literature discussing how societies and subcultures that split off (e.g. the differentiation of the Romance languages, revolutionary Americans, gang members, mother-in-law languages and "women's languages", Urdu v. Hindi) deliberately differentiate themselves linguistically as a means of distinguishing between insiders and outsiders and developing cultural identity.  There are lots of data points on what drives language shift, which language formation requires, but language formation also requires more.

There are purposefully constructed languages or linguistic constructs (e.g. pig latin) although very few of them seem to catch on.  They are like third parties in a two party biased first past the post single member district electoral system.  The viable ones form out of schism in existing ones or are driven by nationalism (e.g. reconstructed modern Hebrew), not to advance intellectually compelling ideas.

I think that the extent to which language formation and change is punctuated rather than evolutionary is greatly underestimated.  But, I'm curious in particular about how more tightly integrated features of a language like phonetics and grammer change relative to less core features like non-core lexical change.  For example, feminism has made some pretty significant changes in these kinds of features recently in English.

In particular, I'm curious about what circumstances might lead to the formation of a new viable language in the modern era.

Srinivasa Ramanujan, India's Mathematical Mystic

Srinivasa Ramanujan was a self-trained mathematical genius and self-styled mystic from Madras, India who died in 1920 at the age of thirty-two. Contrary to the Western scientific tradition, he didn't reveal his methods, other than to say that mathematical observations came to him in dreams provided by a Hindu god, didn't provide proofs, and didn't show his work.

But, observations about number theory and abstract algebra that he made from his death bed in 1920, one of a veritable horde of conjections neither proved nor disproved that he advanced. Some of these have just been proved using modern mathematical methods developed in the last decade.

A televised documentary of his life and accomplishments is coming soon in honor of the 125th anniversary of his birth.

Modern mathematicians are still struggling to figure out how he saw relationships that three generations of mathematicians since him, informed by far more research upon which they build their own work, have not managed to see. What fruitful component was there to his work that has eluded the entire profession in the West for so long?

Few mathematicians believe that Srinivasa Ramanujan was genuinely divinely inspired, but this isn't to say that they don't think he was on to some amazing unstated principal or approach to their trade that they lack, and which makes the relationships more obvious. In the same way, while it was an accomplishment for Wiley to finally prove Fermat's Last Theorem, using methods that were clearly not available centuries earlier when it was formulated, mathematicians still daydream over and ponder what simpler approach (even if not fully rigorous) Fermat could have used to reach his conclusion.

Then again, mathematics is a mature discpline. With a handful of notable exceptions (e.g. fractals, and the simplex method of solving linear equations), particularly in applied mathematics, almost all of the material studied by mathematics students in undergraduate and early level graduate level courses had been worked out by the deaths of Swiss mathematician Leonhard Euler in 1783 and French mathematician Jean Baptiste Joseph Fourier in 1830, several generations before Srinivasa Ramanujan was born.

There is very little being taught in graduate school mathematics classes today that Srinivasa Ramanujan would have either been immediately familiar with and able to grasp, or had the foundational knowledge to figure out in a matter of a few days or weeks. The state of mathematics in 1920 was not so very behind what it is today in a great many of its subfields, including number theory, where he was most renowned.

Number theory remains a subfield of mathematics where many easy to understand problems remain unsolved and where each new advance seems like some sort of miracle not easily inferred by just anyone from the knowledge that came before it in the field.  It has progressed not in some logical and orderly fashion, but with a crazy quilt of zen-like observations whose connection to a larger context and structure of the theorems of the field is obscure.

Is It Possible To Popularize Physics Well?

Lubos Motl has an interesting post inspired by the nomination of the Higgs boson to be a "person of the year" in 2012, notwithstanding the fact that it isn't a person, and reacting to physics blogger Matt Strassler's rant on the inaccuracy of the five sentence story in a magazine directed at general audiences.

He acknowledges that points that Strassler makes are technically correct but goes on to qualify his criticism, in light of the Fool's Errand that any popularizer of physics for the general public faces.  In his view, there are fundamental reasons why popularizing physics for a lay audience is essentially impossible to do well.

In some cases, I would argue that the mistake wasn't "too bad". . . . There must be a moment at which one gives up certain pedagogical ambitions that are utterly unrealistic. While I think that the image of the world as painted by theoretical physics is a major part of the culture of our epoch (and knowing nothing about the W-boson or the genes is as bad as knowing nothing about Shakespeare), I find it obvious that an overwhelming majority of the mankind just can't understand its basics. The reason is an insufficient intelligence, insufficient motivation to follow these things, or both.

Journalists don't have any significant advantage. The average IQ of undergraduate students of communication/journalism is around 112 (compare with physics with 130 at the top). Among the college students, only education (109) and public administration (106) are closer to the average IQ (100). You simply can't expect too visible differences between journalists and average people on the street. They're not elite in any sense. In fact, this "mediocrity" of the writers is imposed upon us because if the journalists were too much smarter than the readers, the readers wouldn't be capable of reading the articles or they wouldn't be willing to do so. . .  

In fact, even if I restrict my attention to people who have dedicated a significant part of decades of their lives to studying physics at home and following events in modern physical sciences, the results are pretty weak. I would say that if most of these people were forced to learn a 2-hour introductory physics lecture in the same way they had to learn at school (otherwise they would be spanked), they would know much more than they know after 20 years of "being interested" in physics. In spite of that, many people are very proud about their "unusual extra knowledge of physics". . . 

A major reason behind this unreasonable ineffectiveness of the "home learning" of physics is that almost all these people pick sources that are full of garbage and myths spread by similarly confused and deluded average people. . . .  Authors of popular books usually contribute to this situation, too – even if they're good experts in their fields. . . .

So physics is interesting as a source of potential miracles, magic, telepathy, superluminal warp drives, and so on. But what about a solid proof that some of these things can't exist? Those insights just don't sell well. People are not interested in genuine physics; they are not interested in the truth whatever it is. They are interested in statements that pander to their prejudices and their special role among their peers. Either this sad fact or the reduced intelligence – or some superposition; it's often hard to disentangle what is at the very beginning – is the primary reason why we don't see any positive progress in the public's understanding of science. The public just doesn't want to understand those things well.

I believe that Matt Strassler still holds totally unrealistic ambitions. It's great to struggle for a better understanding of physics in the general public but if you want too much, you will be fighting the windmills. Various more or less inclusive parts of the public only have a chance to understand physics up to various levels of depth and sensible explanations of physics are likely to be a waste of time if they completely deny this distribution. That's why various types of simplifications (and various degrees of tolerance for certain misconceptions) have to be designed for variously inclusive target groups.

After all, the number of people in the general public who read (close to fundamental/particle/cosmology) physics blogs at least once a week – and redistribute tweets etc. going to physics blogs – is just totally tiny. It's really at most tens of thousands of people in the world. Even if we talk just about "interested laymen", it is just a few parts per million! The genuinely interested laymen aren't too much more widespread than the actual scientists. A larger group follows (and retweets!) science in the "mainstream media" and the distortions of science inevitably follow from this fact because the journalists usually don't know much more than the readers (and can't really know much more, for the communication to work efficiently).

We should think whether the public's belief in the "authority of the mainstream media" is inevitable, whether it brings more advantages or disadvantages, and whether we should struggle to undermine it in some way or not. Of course that there are many events after which I am tempted to think that the answer is a resounding Yes. But when I see what kind of much worse junk may be written in – and read from – some totally non-mainstream sources, I often change my mind again. In most cases, one has to choose between the bad, worse, and worst. ;-)
 

I am not nearly so downbeat in my assessment.  If I was, I wouldn't be a physics blogger.  But, obviously, there are difficulties inherent in trying to explain a discipline that involves at a very fundamental level mathematics that is incomprehensible in the form it is ordinary presented in, even to people who use math professionally like economists, actuaries, commodity traders, criminologists, biologists, physicians, high school math teachers, pharmacists, geologists, and baseball analysts. 

There are a fair number of people trained as physicists, engineers or mathematicans, who aren't practicing physicists who can understand new developments at a deep level (and the Internet makes it far easier for these people to participate in the discussion of the developments and get good primary source information), but there aren't all that many.

Needless to say, most lawyers seek out of the profession because they aren't mathematically inclined and I can read physics papers in their original form and make sense of them only because I was an undergraduate mathematics major who spent a couple of years studying physics and have devoted considerable time from late elementary school onward keeping abreast of new scientific developments on a regular basis - and I absolutely acknowledge my limitations in understanding some of the work being done.  As Motl notes, "genuinely interested laymen", like myself, "aren't too much more widespread than the actual scientists."

Still, there are definitely fundamental concepts of natural philosophy embedded in modern scientific knowledge about physics that are knowable, even by mere educated laypeople without advanced mathematical training, and I belive that there are benefits to making this level of understanding widely known.  The task of conveying this knowledge is one of the missions of this blog.

 

Obscure Genius

Today, I am going to pick on Vladimir Voevodsky, who is certainly an interesting enough fellow in his own right someone who is trained in mathematics (which is his disciplinary field as a professor) with strong interests in problems relevant to fundamental physics and to population genetics. As I note below, if we ever run into each other, I owe him a few drinks for subjecting him to a somewhat down beat assessment of the individual life accomplishments of this extraordinary man in my post today. But, today, I am more interested in talking about the personal niche he is in, which is shared by a great many others, than is personal accomplishment per se.

Voevodsky in a middle aged guy (he is a few years older than I am, but our years studying at institutions of higher education in the United States overlapped) who did his undergraduate work in Moscow, left to the U.S. to do graduate work at Harvard around the time that the Soviet Union fell, is a math professor at Princeton, and won a Field medal, which is basically the Nobel Prize of mathematics, in 2002. He is by any reasonable account a genius.

Voevodsky, like some many other geniuses, however, is an obscure genius. According to a colleague writing a short biography of him, "he defined and developed motivic cohomology and the A1-homotopy theory of algebraic varieties; he proved the Milnor conjectures on the K-theory of fields."

Don't be ashamed that you have no idea what that means.  I struggle to understand it, and I skipped to years of undergraduate math in college and instead spent all three of my years in college taking 300 and 400 level math courses.  Unless you have taken abstract algebra, topology, and real and complex analysis, which are typically offered as 400 level undergraduate course to mathematics majors or 500 level courses for graduate students, you really have not a prayer of meaningfully understanding even a non-specialist oriented description of what is work involves. Few people who aren't professionals in the relevant field know his name (those who are professional in the relevant field hold him in very high esteem), and not even sophomore or junior math majors at esteemed colleges and universities (other than Princeton, of course) have heard of him.

Voevodsky's name isn't familiar to politicians and journalists (except a handful of very sharp science journalists with good memories), won't earn him VIP seats at a ballgame or a nice restaurant outside his home town, and probably gets spelled wrong on his junk mail. A decade from now, more people will remember the name of Missy Franklin, a Denver high school student who won a gold medal for swimming in this year's Olympics, than remember today his shining moment in the sun during the year when he was recognized that year as one of the world's premier mathematicians.

None of this is to put him down. If I met him, I'd know his name and I'd certainly look forward to sharing a beer and talking shop in some dark pub (being Russian, he might be a vodka man, and that would be cool too), my treat.

My point is that our very civilization as an advanced complex technological society rests of the collective achievements of thousands of people like him - the creme de la creme of the upper middle class in who excel in a whole panoply of sometimes obscure professional endeavors. They generally live comfortable upper middle class lifestyles, but are usually neither famous nor genuinely rich on the scale of the thousands of people who have net worths of a hundred million dollars or more. Economically, they live the lives of other successful middle managers in big business and professionals who aren't top level employees of law firms and big businesses.

In truth, we could survive without any one of them and wouldn't know the difference. Lots of people wonder what more could have been discovered is Shakespeare had written another play, if Percy Shelly had written another poem, if Feynman had survived another decade, if Mozart had finished another symphony, or if Fermat had been able to work full time on mathematics rather than merely doing it as a hobby. But, were he to be hit by a bus today, nobody but his family, his graduate students, and his fellow department members at Princeton will dwell on what further conjectures in group theory or topology Voevodsky might of proved or proposed beyond his already formidable accomplishments in another decade once he completes his career. Collectively, the impact of obscure geniuses like Voevodsky in a whole range of professions, is enormous. The group effort that is the produce of their endeavors keeps science and the organization of our society moving ever forward.

This situation certainly isn't particular to mathematics. There are six thousand scientists working at the Large Hadron Collider for instance, many of them doing truly intellectually demanding, cutting edge physics every day, on deadline, as a matter of course and these near geniuses have to have enough social skills to be team players as well. Probably at least one or two hundred of them are geniuses who have made contributions to the enterprise that really no one but a genius could manage and are highly esteemed in their field by their colleagues who can understand their accomplishments and talents. But, fewer than a dozen of them will ever be any more famous than Mr. Voevodsky, even to new generations of students within their field.

Mr. Voevodsky is also notably, not just as an individual Russian mathematician, but also as a member of a numerically small mass migration of the creme of the intellectual elite for the former Soviet Union and Eastern Europe that experienced economic collapse before the recovery began again to the West and, in particular, in large numbers to the United States. The world hadn't seen anything like it since the years immediately before and after World War II. This mass migration of this key elite population has had a rise and fall of great powers level of significance in geopolitics and science that several studies of elite performances in the sciences have documented, although it is little known. It had breathed new blood and new ideas into American science, technology and academics, exposing technical scientific knowledge and ideas that had been isolated in the Eastern block and was little known outside it to a much wider audience where the new ideas have cross-pollinated with Western ones.

Maybe one somewhat obscure Field medal class mathematician like Voevodsky will accomplish in his professional life is a tenth or a twentieth of what a mathematical legend known to all math students at the high school level and beyond, like Euler, did. But, there are at least ten or twenty mathematicians of Voevodsky's caliber, probably more, alive today and they are all working hard at their crafts and standing of the shoulders of the giants who came before them. They also have more colleagues who can understand their work and help prod them on to greater achievements with their own insights. And, very few of them are likely to die young and have their potential prematurely cut short, unlike so many of the famous geniuses of earlier times.

Key Gene Associated With Hominin Leap ID'd

What is it that makes humans different from other extant primates?

A new study points the finger at a small number of genes associated with brain development which are also have some connections to common developmental disorders and mental health conditions, and in particular to a gene called SRGAP2 which is one of the several dozen genes that seem to be most plausible candidates for genes that distinguish hominins from other great apes.

[L]oss of SRGAP2 function accelerates neurons' migration in the developing brain, potentially helping them reach their final destination more efficiently. Moreover, neurons that have decreased SRGAP2 function, due to expression of the human-specific SRGAP2 display more knob-like extensions or spines on their surfaces, making the neurons appear much more like those found in the human brain. These spines enable connections between neurons to form.

The authors of the study think the effect of this mutation would have been dramatic as soon as it emerged.  "If this gene duplication did indeed produce an immediate effect during evolution . . . there must have been a fascinating period in human history characterized by "huge variation" in human cognition and behavior." 

Feynman's IQ

Nobel prize winning physicist and science popularizer Richard Feynman, whose graphic novel biography by Ottaviani and Myrick I recently finished, claimed himself to have an IQ of about 125 on a school test, although he was off the charts in mathematical ability.

The cover of the graphic novel, by the way, features this quote, "If that's the world's smartest man, God help us.", from Lucille Feynman, his mother.

You can also read about his thesis at a recent blog post.

Maybe Neanderthals Were Less Bright Than Given Credit For Being

Two post-Mousterian stone industry complexes are sometimes associated with Neanderthals. But, improved analysis of remains in association with each of those kind of industries, has definitively shown that one is not Neanderthal linked and that the other might not be Neanderthal linked either. This would cast serious doubt on the ability of Neanderthals to innovate technologically at all upon encountered modern humans.

Most researchers accept that before the arrival of anatomically modern humans, Neanderthals had adopted several transitional technocomplexes. Two of these, the Uluzzian of southern Europe and the Châtelperronian of western Europe, are key to current interpretations regarding the timing of arrival of anatomically modern humans in the region and their potential interaction with Neanderthal populations. They are also central to current debates regarding the cognitive abilities of Neanderthals and the reasons behind their extinction.

However, the actual fossil evidence associated with these assemblages is scant and fragmentary, and recent work has questioned the attribution of the Châtelperronian to Neanderthals on the basis of taphonomic mixing and lithic analysis.

Here we reanalyse the deciduous molars from the Grotta del Cavallo (southern Italy), associated with the Uluzzian and originally classified as Neanderthal. Using two independent morphometric methods based on microtomographic data, we show that the Cavallo specimens can be attributed to anatomically modern humans. The secure context of the teeth provides crucial evidence that the makers of the Uluzzian technocomplex were therefore not Neanderthals.

Maju discussed some of the earlier literature referred to in the abstract excerpt quoted above (such as this 2005 article by Mellars) at his old blog, and discusses this article at his new blog.

Mellars argues in particular that transitional European industry stone tools look very similar to Middle Stone Age tools unambiguously associated with modern humans from Africa (from tens of thousands of years earlier), and that it was unambiguously clear that the transitional industries did not appear in Europe until modern humans arrived on the scene (as deduced from carbon dating of nearby European sites definitively associated with modern humans). Thus, it would be an "impossible coincidence" if modern humans didn't have some connection to the transitional industries which were themselves only associated by fairly thin evidence with Neanderthals.

Some of the older literature comes from Denver's resident expert on Neanderthals, Julien Riel-Salvatore, who cast doubt on the Neanderthal association with the Uluzzian with multiple lines of strong circumstantial evidence as opposed to the direct evidence of the most recent paper. Riel-Salvatore also noted in his 2010 paper the doubtfulness of prior associations of the teeth found with Neanderthals, which today's research bears out.

Riel-Salvatore also discussed at his blog the case against Neanderthal involvement in the Châtelperronian industry. The association of Neanderthals with the Châtelperronian is based on just two digs and the association of one of the two sites was seriously questioned by by Bar-Yosef, O., & Bordes, J.G. in their article "Who were the makers of the Châtelperronian culture?" Journal of Human Evolution (2010) DOI: 10.1016/j.jhevol.2010.06.009, on the theory that there is strong evidence of muddling of the stratiography between an older clearly Neanderthal layers and the Châtelperronian that disfavors that associatioon.

Bar-Yosef and Bordes were less trenchant in their examination of the second site, however. He notes in that post that, "Ultimately, though, the revision proposed by Bar-Yosef and Bordes needs to be taken cautiously, especially as it concerns the St. Cesaire remains. One thing it doesn't do is associate the Chatelperronian with modern humans," as the latest research does for the Uluzzian. More particularly, he explains that:

At St. Césaire, where the the secondary burial of a Neanderhal was found in the Chatelperronian, Bar-Yosef and Bordes argue that the presence of distinct 'Mousterian' and 'Chatelperronian' components of the lithic industry and the fact that not all artifacts show a similar state of preservation suggest caution is needed before we can accept that it was not a mix of Mousterian and Chatelperronian levels. Because the burial is found in the upper (of two) Chatelperronian level, they argue that it was probably not deposited by occupants of the site anyway, implying that Neanderthals who did not make Chatelperronian tools might have buried one of their deceased at St. Césaire, perhaps in an effort to mark the site as theirs following the arrival of whoever made the Chatelperronian.

In my view, Bar-Yosef and Bordes' case is much stronger for Grotte du Renne than it is for St. Césaire, especially since bone refitting at St. Césaire has recently demonstrated that mixing between the Mousterian and the Chatelperronain was a negligible occurrence at the site (Morin et al. 2005). The need to invoke an explanation that doesn't depend strictly on stratigraphic of artifactual data also weakens their overall argument. I say this because if their argument is followed to its logical end, it would mean that, even if you found that unheard of goody that would be a site containing only Chatelperronian layers and thus could exclude stratigrpahic mixing as an explanation, the presence of Neanderthal remains (or at least of a secondary Neanderthal burial) could still be explained away as a result of self-affirming Neanderthals claiming a stake to a given bit of territory. That's not to say that it's impossible, of course, and I will concede that the St. Césaire burial is the only relatively undisputed case of a Neanderthal secondary burial, so the practice was never common and who knows what it really might have meant, as the authors concede. Given that this is the case, though, you wouldn't expect a very unusual behavior to be the preferred manner in which Neanderthals would have marked their territories in the context of encounters with new groups of hominins.

The debate now, is pretty much limited to whether the Châtelperronian was actually associated entirely with modern humans (a possibility discounted entirely until a couple of years ago), or simply involved efforts by Neanderthals (or hybrid Neanderthals perhaps) to copy contemporaneous modern human industries.

Alternately, a hybrid Neanderthal at the modern human-Neanderthal boundary might be a natural candidate for an unusual secondary burial at a possibly abandoned Châtelperronian site (don't forget that all modern humans were semi-nomadic hunter-gatherers at the time), if that industry was a modern human one, that would be better motivated than a simple effort of the Neanderthals to mark their territory. The secondarily buried Neanderthal at that site might, for example, have had a modern human father who lived there when the buried individual was conceived (or the mother of a hybrid child from such a union). We know that some Neanderthals did bury their dead and that there was some symbolic element to this practice (as indicated, for example, by grave goods).

If no Neanderthals, or at least no non-hybrid Neanderthals, engaged in transitional industries, and they instead were unable to innovate beyond the 200,000 year old Mousterian stone industry even in the face of exposure to more advanced modern human tool making, the natural inference is that they really were significantly less intelligent than modern humans. In particular, they may have either lacked the ability to learn and innovate, instead acting more on instinct, or may have lacked the mental capacity to make more sophisticated tools in general because they involved some sort of evolutionary leap in ability (perhaps in mental ability, or perhaps in fine motor skills) that they couldn't handle.

Issues Worth Examining

Usually I discuss new findings in science. Today, I'll identify a number of issues that science has, nearly has, and may have the tools to answer, but have not yet been resolved.

1. Is there any archaeological evidence of Sumerian or Egyptian cultural influence to the north of the Aegean and Anatolia and the Mediterranean Coast?

We know that the area north of the Aegean and Anatolia, particularly the Balkans, was a stopping off point for the further Neolithic settlement of Europe by farmers and herders the earliest of which is the Linear Pottery Culture (LBK). There is a "fan" of population genetic influence (e.g. Y-DNA haplogroup E) that appears to be North African in origin that extends well into the Balkans. There are multiple eras when this could have arrived: early Neolithic, during the Greek silver and golden ages, during the Roman era, during the Byzantine era, as part of Slavic expansion, or under the Ottoman Empire. But, population movements in the region after the LBK and prior to any potential Greek influence are obscure.

The Egyptian and Sumerian empires are not known to have ever extended beyond Southern Anatolia and perhaps a few fringe Aegean islands in recorded history.

There are some suggestive cave paintings in the Caspian Sea that would seem to show Egyptian style boats at a time when the Egyptians would have had that kind of boat. There is some evidence of fairly sophisticated canal system connecting the Black and Caspian Seas at some point in history. There have also been some suggestions of a Sumerian linguistic influence on some or all Uralic languages.

As one of the earliest loci of Indo-European language speakers, these traces would have to be quite early. Also, Egyptian record keeping and Sumerian records, to my knowledge, do not document these kinds of expeditions, but these records were hardly comprehensive, particularly in the earlier eras.

Finding such a link, or definitively ruling it out, would be helpful either way in piecing together chains of causation in prehistory.

2. The sporadic v. familial model in evaluating the etiology of IQ.

Considerable research has been devoted to the causes of mental retardation, particularly where it arises without a family history of it, and considerable research has been devoted to establishing that IQ, in general, has a strong hereditary component that can be discerned from familial similarities in IQ at different degrees of relatedness.

One area that probably deserves more research is to examine "sporadic" instances of high IQ. In other words, what can we learn about the nature of IQ from looking genetically and from a nurture perspective at very high IQ people with much lower IQ parents. Are these mostly cases of parents who had good genes that were suppressed by bad environments that were not shared by the child? Are these cases of new mutations in the child that were not present in the parent? Are these cases of recessive genes that did not express in either parent? Are these casees of exceptionally good parenting choices? Are these cases of inaccurately assigned paternity? Or what?

3. Where does South Asian Y-DNA haplogroup T come from?

Areas more or less similar to the proto-Dravidian area of South Asia, and also certain tribal groups in Eastern South Asia, have high concentrations of Y-DNA haplogroup T. What kind detailed subtyping of these haplogroups tell us about where they fit in the phylogeny of Y-DNA haplogroup T and whether these Y-DNA types are autochronous or have some specific geographic origin elsewhere? What can study of these haplogroups tell us about time that this haplogroup emerged in that location?

It does not appear to have origins in Pakistan and is centered on the Eastern side of South Asia with a stark discontinuity between it and the Northwest. If it is part of either an Ancesteral North Indian or Ancestral South Indian genetic package at all, it is a part of the Ancestral South Indian genetic package that is not associated with Harappan or Indo-Aryan influence. Yet, ASI is often seen as indigeneous to the subcontinent, while Y-DNA haplogroup T has clear affinities to the European/West Asian/Northern and Eastern African region (i.e. "Western influence.") It could be that autosomal analysis is conflating Western influence via Harappan and Indo-Aryan populations and Western influence associated with Y-DNA haplogroup T associated with a separate, distinct and earlier migration, since the two Western influences may be closer genetically to each other than they ANI and ASI are to each other.

My intuition is that detailed study will show origins of the South Asian subtypes in phylogenies rooted in Southern Egypt, Sudan, Ethiopia and Somolia, and that an appropriately chosen mutation rate aging methodology will be consistent with the South Asian Neolithic and proto-Dravidian language, suggesting that migrants from South Asia were instrumental in this historical events. But, population genetics can shed much better light on the question. Detailed phylogenies of Y-DNA haplogroup T have been done, but they did not extend to South Asian samples, so study of those samples is a final step necessary to prove or disprove the hypothesis that Y-DNA haplogroup T men were instrumental in the formative period of Dravidan culture.

4. What distinguishes socioeconomically successful people who are similar in IQ, have only a high school education and have similar socioeconomic status to begin with?

A junior high school or high school teacher in a low income neighborhood has a great many students of the same socioeconomic status, and whatever environmental influences out there impact IQ have already transpired for the most part. These teachers have the hand that they have been dealt and so do their students at that point.

Lots of studies show education and IQ as pivotal for success in low socioeconomic status kids. But, what about the kids for whom earning a college degree is not a realistic option given their mediocre academic performance to date, even if they are able to stick it out and graduate from high school?

What choices and factors distinguish the winners and losers in life, in terms of socioeconomic success, once these parameters are set?

Insufficient good research looks at this issue which is a practical concern to a very large numbers of teachers, mentors, and kids. Good research on this point could provide an empirical basis to enhance middle school and high school curriculums for a group of students who often simply receive a watered down version of a college preparatory curriculum directed towards an educational trajectory that they are very unlikely to follow with success.

A great deal of effort has been devoted to researching how to improve academic performance, but despite study after study that shows that very little consistently improves academic performance in a consistent way once variables like socioeconomic class and past academic performance and IQ are controlled for, despite herculean efforts to find approaches that do, perhaps at least a little more research should be devoted not to improving the academic performance of these academically mediocre kids, but to accept for a moment that some kids, indeed a great many kids, are going to be academically mediocre, and to figure out in a way that accepts this as a given, what their best options in life are and what choices are most important to their lifetime prosperity.

Also, to the extent that there are inborn personality traits that have an impact on this result (something shown in high IQ individuals already by the Termain study, for example), what can we say about optimal approaches for kids with different personalities profiles?

Perhaps some of these lessons can be replicated.

5. What distinguishes misdemeanor recidivists?

Felony recidivism is heavily studied.

Misdemeanor recidivision (and misdemeanor sentencing in general) is not. We need more basic information about who misdemeanor recividists are, how differential treatment of them in the criminal justice system can impact crime rates and criminal justice system resources, how authorized sentences differ from imposed sentences by offense type, offender type, and aggravating circumstances, and how discretion in the criminal justice system is exercised both in bond matters and plea bargaining and sentencing in misdemeanor criminal matters.

You Get More From Your Parents Than Parenting

Lots of people are raised for substantial parts of their lives by people whom they are not genetically related to, and a new study of Korean adoptees from the 1950s and 1960s has revealed once again that a rather surprisingly large share of the way that kids turn out is congenital rather than a product of the way that they were raised.

Having a college educated mother increases an adoptee’s probability of graduating from college by 7 percentage points, but raises a biological child’s probability of graduating from college by 26 percentage points. In contrast, transmission of drinking and smoking behavior from parents to children is as strong for adoptees as for non-adoptees. For height, obesity, and income, transmission coefficients are significantly higher for non-adoptees than for adoptees. In this sample, sibling gender composition does not appear to affect adoptee outcomes nor does the mix of adoptee siblings versus biological siblings.

Factors like religious affiliation and linguistic accent are also very strongly cultural. Nobody is born Christian or Buddhist, or speaking Spanish or English. Genetics may influence you attitude towards religion, or your likelihood of having a learning disability related to reading, but it won't determine the content of your religious beliefs or the language that you will learn.

But, parental income at the time of adoption has virtually no effect on adopted child income. Parental education does have a modest effect on adopted child educational level (parents who went to graduate school have adopted kids with half a year more of education than those who merely graduated from high school), but the effect is really strong only for parents who don't have at least a high school diploma (those kids get dragged down). In contrast, parental income and education have a rather pronounced effect on the the incomes and educational levels of biological children suggesting that these outcomes are mediated by factors like hereditary IQ and personality effects.

This doesn't necessarily mean that your parents alone are your destiny. Quite extensive studies have shown that there is a fairly wide range of stable differences in all sorts of traits between even full blooded siblings on factors from IQ to personality and that those differences impact life outcomes. Almost no intelligence or personality or mental health traits are 100% hereditary or even much more than 85% hereditary, and most hover at the 50% level or less.

There is also a fair amount of evidence to show that really bad parenting and early childhood deprivations or physical traumas can screw anyone up no matter how much potential that person may have had at birth. Genuine poverty, malnutrition, lead poisoning, prolonged isolation, and abuse are all bad for kids no matter how promising they are (although there are even genes that govern how well kids can cope with some of these adversities, a trait sometimes described as resilience).

But, given the intense amount of effort the parents put into deciding precisely how to raise our children, parenting choices make less of a difference than one would intuitively expect. Princes raised by peasants really do generally grow up to be princes, royal bastard are going to tend to outperform their ordinary siblings, and kids raised in circumstances far more favorable than those they were born in because they are adopted generally underachieve relative to the biological children of their adoptive parents and have less in common with their siblings than you would expect from a shared upbringing. It may have a ring to the monarchist propaganda that Disney likes to produce, but there is truth to it. The myth of Achilles, who was a prince raised by farmer parents as their own who rises to prominence, is closer to real life than the Prince and the Pauper.

Indeed, there are at least one or two studies out there that show that decent parenting from just about anyone is fine. A good step-parent or adoptive parent or extended family member in lieu of a parent can raise you well enough to reach essentially the same potential you could have if raised by a biological parent - or better if a biological parent's exceptionally bad parenting was factor that could have dragged you down.

It is hardly surprising that assortive mating should strength social class divides. If people who have what society rewards have kids with other people who have the same traits, and people who lack that have kids with other people who lack that, we expect that there kids are more likely to reproduce their status than in a society where couples form at random or are deliberately unequal in traits that society rewards, which will tend to produce more variability between siblings and more averaging out.

More paradoxically, each generation that society is meritocratic should strength class divideds in future generations. Some people from modest beginnings will always be more talented than their parents, and some people with talented parents will always have less of what made their talents successful. Regression towards the mean is to be expected, and the less talent matters the less talent will be associated with social class and the more vulnerable the social class system will be to being upset by talented people born in a lower socio-economic class usurping less talented people born to privilege.

By all accounts, American marriages are more assortive than they used to be, and we have had roughly two full successive generations of a relatively meritocratic society. The longer this continues, the more stark social class divisions can be expected to become, with really no obvious limits. A few centuries of carefully preserved meritocracy and assortive mating should paradoxically greatly reduce social class mobility and make the gradations within social classes more fine, to the extent that social class divisions are a product of individual personal traits rather than the nature of the slots the arise from our current technology and economic system. A hunter-gather society, for example, can support only so much social class stratification.