Do We Really Need Either Dark Matter Or Modified Gravity?

This article isn't hot off the presses, but was referenced in the comments at the Triton Station blog. I am highly skeptical of the conclusion that Newtonian physics without dark matter or modified gravity can explain the dynamics of the Milky Way galaxy adequately, contrary to a wealth of literature to the contrary.

Vertical stellar kinematics+density can be used to trace the dark matter distribution (or the equivalent phantom mass in a Modified Newtonian Dynamics (MOND) scenario) through the Jeans equations. 

In this paper, we want to improve this type of analysis by making use of the recent data of the 6D information from the Gaia DR3 survey in the anticenter and the Galactic poles to obtain the dynamical mass distribution near plane regions, including extended kinematics over a wide region of 8 kpc < R < 22 kpc, ∣z∣ < 3 kpc. 

Our conclusions are as follows: 

(i) the model of the spherical dark matter halos and the MOND model are compatible with the data; 

(ii) the model of the disky matter (with density proportional to the gas density) is excluded; 

(iii) the total lack of dark matter (there is only visible matter) within Newtonian gravity is compatible with the data; for instance, at solar Galactocentric radius, we obtained Σ = 39 ± 18 M⊙ pc^−2 for z = 1.05 kpc, compatible with the expected value for visible matter alone of 44 M⊙ pc^−2, thus allowing zero dark matter. Similarly, for R > R⊙, z = 1.05 kpc, Σ = 28.7 ± 9.6, 23.0 ± 5.7, 16.9 ± 5.8, and 11.4 ± 6.6 M⊙ pc^−2, respectively, for R = 10, 13, 16, and 19 kpc, compatible with visible matter alone. 

Larger error bars in comparison with previous works are not due to worse data or a more awkward technique but to a stricter modeling of the stellar distribution.

Martín López-Corredoira, "Milky Way Dark Matter Distribution or MOND Test from Vertical Stellar Kinematics with Gaia DR3" 978 ApJ 45 (December 24, 2024) DOI 10.3847/1538-4357/ad94f5 (open access).

Where Does Language Complexity Evolve?

I'm not entirely sold on this article's conclusion about the circumstances in which language complexity evolves, at least not based upon the data presented, even though there is good evidence that large numbers of language learners tend to reduce grammatical complexity.

Polysynthetic languages are very common in the New World and just across the Beringian land bridge from it (which could also be connected to the Paleo-Siberian cases), suggesting that most instances of it could be derived from a common source creating a Founder effect. 

Also, while these languages are small and isolated now, this hasn't always been the case. Athabaskan-Eyak-Tlingit and Nahuatl, for example, historically were quite expansive and had lots of contact with other language families.

The second cluster is from Aboriginal Australians and Papuans who derive from the first wave of modern human migration Out of Africa and into Asia around the time of the Toba eruption. 

There is a third cluster in the Caucuses, involving just one of the language families there, which are associated with early migrants from the first wave of Fertile Crescent agriculture in the highlands of West Asia. 

There are apparently other instances in South Asia and East Asia.

A handful of major language expansions, none of which happened to be polysynthetic make up a huge share of all languages spoken today. These include the Indo-European language family, the Afro-Asiatic languages, the Bantu language family, the Dravidian languages, and the arguable Altaic language family. European and Chinese colonial empires further reduced the size of many languages (long after their features were well intact), for reasons unrelated to language complexity. 

There are polysynthetic or borderline polysynthetic languages listed in the following major language families: the Sino-Tibetan languages (seemingly all in the Tibetan-Burmo branch), the Austroasiatic languages (3 Munda languages in Northeast India), the Austronesian languages (5 borderline seemingly Formosan languages) 

If only a minority of pre-expansion languages were polysynthetic, it wouldn't be surprising if the main expanding languages didn't end up including them.

Significance

A global test reveals statistically robust support for the hypothesis that complex word forms are more likely to develop in isolated languages. Polysynthesis, where words are built from many units to convey complex meanings, is more likely to occur in smaller populations and less likely to occur with many languages in contact. By building a global database of polysynthetic languages and analyzing in a phylospatial framework, this study highlights the potential for macroevolutionary methods to test hypotheses about language evolution and contribute to long-standing debates in linguistics.

Abstract

Evolution of complexity in human languages has been vigorously debated, including the proposal that complexity can build in small, isolated populations but is often lost in situations of language contact. If it is generally true that small, isolated languages can build morphological complexity over time, but complexity tends to be lost in situations of language contact, then we should find that forms of language complexity that have evolved multiple times will tend to be associated with population size, isolation, and language age. 

We test this hypothesis by focusing on one particular form of morphological complexity, polysynthesis, where words built from many parts embody complex phrases. By assembling a global database of polysynthetic languages and conducting phylospatial analyses, we show that languages with highly complex word morphology are more likely to have small population sizes, less likely to occur with many other languages in direct contact, and have a greater tendency to be on long phylogenetically isolated lineages. 

These findings are consistent with the hypothesis that languages that evolve in isolation for long periods may be more likely to accrue morphological complexity. Polysynthetic languages also tend to have higher levels of endangerment. Our results provide phylogenetically informed evidence that one particular form of complex language morphology is more likely to occur in small, isolated languages and is prone to loss in contact.

Lindell Bromham, Keaghan Yaxley, Oscar Wilson, and Xia Hua, "Macroevolutionary analysis of polysynthesis shows that language complexity is more likely to evolve in small, isolated populations" 122(24) PNAS e2504483122 (June 12, 2025) (pay per view; but open access supplemental materials).

The languages counted as polysynthetic and borderline, according to the Supplemental Materials, are below the fold.