Ancient DNA Refines New World Settlement Paradigm

Overview

A new pre-print based on analysis of ancient DNA from a number of far northern populations in North America and Siberia has refined what we know about the waves of pre-Columbian migration to North American after the founding population of American entered North America from the Beringian land bridge not later than about 14,000 BCE.[1] 

There is genetic variation that is found in Canada and the United States, but not in Latin America, which is not attributable to later waves of pre-Columbian migration. This was due either to founder effects in a population that rushed down the Pacific coast over a period of less than 2000 years and became ancestral to all indigenous Americans outside of Canada and the United States, or due to population structure in the original founding population of the Americas.

All pre-Columbian genetic ancestry extant in modern gene pools in the Americas (with the possible exception of part of the ancestry found in certain Amazonian tribes whose source is not well understood which is sometimes described as "Paleo-Asian" [2]) is attributable to this initial founding population (often called "First Americans" in the literature) or two main subsequent migrations from Siberia from genetically related (but not identical) Siberian populations. 

The first wave of subsequent pre-Columbian migration, ca. 3500 BCE (the current pre-print makes the case for an approximate 3000 BCE date [3]) gave rise to the Paleo-Eskimos who ceased to exist as a distinct population around the time that the "Neo-Eskimos" arrived, which is also the source, a few centuries later, of the distinctive genetic ancestry of the Na-Dene people (such as the Tlingit people of Southeast Alaska, and the Apache and Navajo people of the American Southeast), which is otherwise shared with the founding population of the Americas.

The second wave sometime between 1100 BCE and 200 BCE (probably closer to 200 BCE, given the archaeological evidence) gave rise to the Neo-Eskimos such as the Inuits, after substantial admixture with people descended from the founding population of the Americas. (The Na-Dene people were not a source of admixture with the Neo-Eskimos.)

Incidentally, this three wave model had already been predicted based upon archaeological and linguistic evidence several decades before genetic evidence confirmed this model.

There have been a few other well documented instances of much more incidental pre-Columbian contact after the founding population arrived with the Americas (for example, Vikings ca. 1000 CE in Eastern Canada), but none of the other cases left any genetic legacy in the Americas. Also notably, all of those credibly documented contacts post-date the Paleo-Eskimo migration, and all but one doubtful case of a single alleged New World apple seed found in India that was carbon dated to 2000 BCE, post-date both of these migration waves. For example, the Asian War Complex arrives ca. 700 CE, about the same time as the Neo-Eskimos reach Alaska proper, an a previous major bow and arrow technology innovation arrives ca. 400 BCE around the time of first contact between pre-Neo-Eskimos from Asia and and indigenous populations in the Bering Straight. Critically, all First American populations were still isolated from all other modern humans for more than 10,000 years (a time depth that, among other things, is so great that it impossible to reconstruct a proto-Amerind language from known indigenous American languages).

The Story Of The Na-Dene

The genetic distinctiveness of the Na-Dene (a.k.a. Athabaskan) indigenous populations of North America derives from admixture of Paleo-Eskimos in Alaska ca. 3000 BCE plus or minus a few centuries (genetic and archaeological evidence suggests that they arrived ca. 3500 BCE [4], giving rise to the Saqqaq culture and started to admix several centuries later) with indigenous First Americans (whose ancestors arrived over the Beringian land bridge by not later than about 14,000 BCE). The initial admixture percentage in ancient Northern Athabaskans was roughly 25%-40%. Over time, the Paleo-Eskimo admixture percentage in the Na-Dene has been diluted to about 10%, but all Na-Dene populations have this ancestry which is almost completely absent from non-Na-Dene language speakers.

Genetic evidence also supports the Dene-Yeniseian linguistic hypothesis that the Na-Dene languages have a linguistic family relationship with the Yeniseian language family of Siberia of which the sole surviving language is the Ket language. Specifically, ancient DNA from a population in the Ust'-Belaya culture of Chukotkan in Siberia, which is ancestral to the Paleo-Eskimos, shows evidence of genetic relatedness to both the Paleo-Eskimos and a western Siberian group related to Kets. The pre-print notes that: 

striking parallels in archaeological and genetic results suggest that admixture between proto-Paleo-Eskimos and Siberian lineages in Chukotka took place not long after they diverged [ca. 4300 BCE], indicating that cultural contact between these groups at this time almost certainly occurred as well. This result has implications for archaeology and historical linguistics[.]

At least two "push factors" drove Na-Dene tribes such as the Navajo to migrate to the American Southwest around 900 CE, and may have also been involved in the migration of the Tlingit Na-Dene tribes to southeastern Alaska and Pacific coastal Canada. One was the arrival of "Neo-Eskimos" (e.g. the founding population of the Inuits who were part of the Birnirk and Thule cultures) in western Alaska ca. 650 CE to 850 CE. The other was a massive volcanic ash fall ca. 900 CE. There was little or no Na-Dene genetic introgression into Neo-Eskimo populations. 

In the American Southwest, there was also a "pull factor" which was the control vacuum created when the society of the ancient Puebloan people (a.k.a. the Anasazi) collapsed, in part due to a major drought associated with the Medieval Climate Anomaly (which quite possibly was related, in part, to the volcanic eruptions that took place at about the same time that the MCA began) that may have partially encouraged Na-Dene people who had already migrated to the Canadian heartland to migrate South, or may have made them more successful as a potentially competing collapsed when, or not long after, they arrived.

It is also worth noting that there were major innovations in bow and arrow technology ca. 2500 BCE, which had previously been stagnant since 10,000 BCE, which might have coincided with the arrival of the Paleo-Eskimos and the increasing prevalence of the Arctic Small Tool tradition.

The Story of the Modern Eskimos

Some members of the population the Siberian population ancestral to the Paleo-Eskimos migrated to North America. Others remained in Siberia and gave rise to a sub-population ca. 1500 BCE (about 1500 years after the first wave admixed with the Na-Dene) that was ancestral to modern "Neo-Eskimos" such as the Inuits who arrived in western Alaska ca. 650 CE to 850 CE and are known to archaeologists as the Birnirk and Thule cultures. About 43% of the modern Neo-Eskimo population's ancestry is attributable Asian migrants from this population and this population is also the source of mtDNA D2a in Neo-Eskimos. 

The balance of Neo-Eskimo ancestry [5], arises from northern non-Na-Dene descendants of the first wave of migrants to North America, and in particular, from descendants of the indigenous southwestern Alaska and Kodiak Island Ocean Bay tradition (which flourished ca. 4800 BCE to 2500 BCE) in which a lot of the technological innovations involving year round maritime hunting were invented. In contrast, early "Paleo-Eskimo people used marine resources on a seasonal basis only, depended for the most part on hunting caribou and muskox, and lacked sophisticated hunting gear that allowed the later Inuit to become specialized in whaling." Thus, while the new influx of genes and their language had Asian origins, their maritime hunting technologies were made in North America.

The admixture that gave rise to the modern Neo-Eskimo population had already substantially run its course by 200 CE when ancient DNA reveals an already admixed Neo-Eskimo who was part of the Old Bering Sea culture which commenced ca. 200 BCE.

The admixture that gave rise to the ethnogenesis of the Neo-Eskimos predated the Ipiutak culture of western Alaska which emerged ca. 300 CE.

It is possible that some or all of the admixture and ethnogenesis that gave rise to the Neo-Eskimos took place in the Old Whaling culture of western Alaska (ca. 1100 BCE to 700 BCE), the Choris culture of western Alaska (ca. 700 BCE to 500 BCE) or the Norton culture of western Alaska (ca. 500 BCE to 200 BCE). There isn't enough ancient DNA data available to be more specific. Archaeological data tends to support a date at the more recent end of that range, such as the tail end of the Norton culture [6].

End notes and language from the body text of the paper supporting this summary, with editorial emphasis, additional hyperlinks to prior posts at this blog, and headings, appear below.

[1] The 17 new ancient DNA samples were as follows:

We generated new genome-wide data from 11 ancient Aleutian Islanders that date from 2,320 to 140 calBP, three ancient Northern Athabaskans (McGrath, Upper Kuskokwim River, Alaska, 790 – 640 calBP), two Neo-Eskimos of the Old Bering Sea culture (Uelen, Chukotka, 1,970 – 830 calBP), and one individual of the Ust’-Belaya culture (Ust’-Belaya, Chukotka, 4,410 – 4,100 calBP)[.]

[2] Recently sequenced ancient DNA from an actual Paleo-Asian shows genetic affinity to this Amazonian population. As explained here (in French):

Many of the current Native American populations share alleles derived from the Tianyuan individual, but three South American populations (Surui and Karitiana of Brazil and Northern Argentina and South Bolivia Chain) share more derived alleles with the Tianyuan individual than all the other Amerindian populations. These Amerindian populations also share more derived alleles with the current Papuan and Onge populations than all other Amerindian populations. These results suggest that at least two different ancestral populations contributed to the ancestry of the Amerindian populations. The former Indian individual Anzick-1 does not share more alleles derived with the former individual of Tianyuan (or with the current Papuans and Onges) than other Amerindian individuals. Thus Surui, Karitiana and Chane can be modeled as a genetic mixture between other Amerindian populations and an ancient population related to the former individual of Tianyuan, Papuans and Onges (9 to 15%).

This new study suggests is a much higher percentage (the previous study thought 2%) and is much more geographically widespread (only the Surui) than the previously study that I analyzed in determining the source of apparent Paleo-Asian ancestry in South America leading to my conclusion that:

The most likely explanation for the Paleo-Asian ancestry in tribes in the Amazon, in my opinion for reasons set forth above the break, involves the integration of a small number of individuals who arrive shortly before migration to the Americas begins, who are from a now extinct Asian population with some Paleo-Asian ancestry, into one of the tribes of the Beringian population that had been there for thousands of years. (I imagine a canoe cast in the wrong direction by a storm, or a small nomadic hunter-gatherer family, perhaps an adventurous one, that wanders in a new direction for afield from their kin for some reason.) Their new tribe happens to be in or near the vanguard of those migration along the Pacific Coast, which isolates them genetically from populations that follow them at a slower pace. Members of this tribe end up being the first settlers of the part of the Amazon where these genes are found and cease to migrate or expand as neighboring areas now have their own human populations. There could also have been a small number of related individuals or tribes with these genes who ended up in more accessible areas but went extinct due to post-Columbian New World diseases or some other pre-Columbian or post-Columbian mishap.

Previous studies as inconclusive as the first round at data I looked at with similar findings, have not been replicated.

[3] The introduction of the pre-print states:

The archaeological record in the Arctic provides clear evidence for the spread of PaleoEskimo culture, which spread across the Bering strait about 5,000 calBP9,11-13, and expanded across coastal Alaska, Arctic Canada and Greenland a few hundred years later. Direct ancient DNA data has proven that the Paleo-Eskimo cultural spread was strongly correlated with the spread of a new people7,8 that continuously occupied the American Arctic for more than four millennia until ~700 calBP9,14,15. A long-term cultural, and likely linguistic and genetic, boundary was established upon their arrival, which separated populations in the coastal Arctic tundra from indigenous Native American groups who populated the interior forest zone and were plausibly ancestors of present-day Na-Dene speakers16. Paleo-Eskimo archeological cultures are grouped under the Arctic Small Tool tradition (ASTt), and include the Denbigh, Choris, Norton, and Ipiutak cultures in Alaska and the Saqqaq, Independence, Pre-Dorset, and Dorset cultures in the Canadian Arctic and Greenland9 . The ASTt source has been argued to lie in the Syalakh-Bel’kachi-Ymyakhtakh culture sequence of East Siberia, dated to 6,500 – 2,800 calBP17,18.

The sources cited in that passage are as follows:

7. Rasmussen, M. et al. Ancient human genome sequence of an extinct Palaeo-Eskimo. Nature 463, 757–762 (2010).  

8. Raghavan, M. et al. The genetic prehistory of the New World Arctic. Science 345, 1255 (2014).   

9. Friesen, T. M. Pan-Arctic population movements: the early Paleo-Inuit and Thule Inuit migrations. The Oxford Handbook of the Prehistoric Arctic, ed. Friesen, T. M., Mason, O. K. New York: Oxford University Press. 673–692 (2016).  

11. Park, R. W. The Dorset-Thule transition. The Oxford Handbook of the Prehistoric Arctic, ed. Friesen, T. M., Mason, O. K. New York: Oxford University Press. 417–442 (2016).  

12. Prentiss, A. M., Walsh, M. J., Foor, T. A. & Barnett, K. D. Cultural macroevolution among high latitude hunter–gatherers: a phylogenetic study of the Arctic Small Tool tradition. J. Archaeol. Sci. 59, 64–79 (2015).  

13. Tremayne, A. H. & Rasic, J. T. The Denbigh Flint Complex of Northern Alaska. The Oxford Handbook of the Prehistoric Arctic, ed. Friesen, T. M., Mason, O. K. New York: Oxford University Press. 303–322 (2016). 

14. Friesen, T. M. Contemporaneity of Dorset and Thule cultures in the North American Arctic: new radiocarbon dates from Victoria Island, Nunavut. Curr. Anthropol. 45, 685–691 (2004).  

15. Friesen, T. M. & Arnold, C. D. The timing of the Thule migration: new dates from the western Canadian Arctic. Am. Antiq. 73, 527–538 (2008).  

16. Potter, B. A. Archaeological patterning in Northeast Asia and Northwest North America: an examination of the Dene-Yeniseian hypothesis. The Dene-Yeniseian Connection, ed. Kari, J., Potter, B. A. Anthropological Papers of the University of Alaska: New Series 5, 138–167 (2010). 

17. Powers, W. R. & Jordan, R. H. Human biogeography and climate change in Siberia and arctic North America in the fourth and fifth millennia B.P. Philos. Trans. R. Soc. Lond. A 330, 665–670 (1990).  

18. Dumond, D. E. & Bland, R. L. Holocene prehistory of the northernmost North Pacific. J. World Prehist. 9, 401–451 (1995). 

[4] The dating of the Saqqaq culture's arrival in North America is based upon the following language from a 2010 article in Nature sequencing ancient DNA from a Saqqaq individual who died ca. 2000 BCE, the first case ever in which human ancient nuclear DNA was sequenced (emphasis added):

We additionally used a population genetic model to obtain maximum likelihood estimates of the divergence times between the Saqqaq individual and the reference populations (Supplementary Information). The population with the shortest divergence time was Chukchis, with an estimated divergence time of approximately 0.043 (±0.08) Ne generations, where Ne is the effective population size. In contrast, the estimated divergence times to the other closely related populations—Na-Dene, Koryaks and Nganasans—were 0.093, 0.11 and 0.089, respectively. The estimated divergence time to the Han Chinese, a more distantly related population, was 0.20. These estimates can be converted to estimates of years or generations, by making assumptions regarding the effective population sizes of the reference populations. The effective population sizes are in general unknown, but can be estimated from DNA sequence data, and are generally much smaller than the census sizes (Supplementary information). We found no evidence in favour of changes in population size. Even when accounting for the uncertainty in the estimate of the mtDNA mutation rate, and possible biases related to the genotyping data, it is still unlikely that Ne >5,000, providing a maximal divergence time between Chukchis and Saqqaqs of 175–255 generations or between 4,400 and 6,400 years. The oldest archaeological evidence of the Arctic Small Tool tradition in the New World is from Kuzitrin Lake, Alaska, dating back ∼5,500 cal. yr bp, indicating that the ancestral Saqqaq separated from their Old World relatives almost immediately before their migration into the New World.

The current pre-print corroborates the genetic link between Paleo-Eskimos and the Chukchis of Siberia inferred in 2010.

Another scholar put the arrival of the Saqqaq, who are associated with the Arctic Small Tool Tradition in North America (which it notes is derived in turn from Eastern Siberian) at 2500 BCE. But, this seems too recent, given that the Saqqaq were already present in Greenland by that point. Encyclopaedia Brittanica dates the origins of the tradition to 3000 BCE. An archaeology wiki puts the date at 2200 BCE, but has its most recent source of authority for this position in 1984. The 2010 Nature article cites a more credible source than any of these for its 3,500 BCE date of arrival in North America: Harritt R. "Paleo-eskimo beginnings in North America a new discovery at Kuzitrin lake, Alaska." 22 Etud Inuit. 61-81 (1998).

As of 1999, archaeological efforts to identify a Northeast Asian antecedent to the Arctic Small Tool tradition or other physical anthropology antecedents to the Paleo-Eskimos of Canada and Alaska, had not be very fruitful, but much of this was due to a lack of trying in an area that hadn't been very intensely studied, at least at that point in time.

Pottery starts to appear in Siberia around 5500 BCE, but without agriculture or even pastoralism, and may not have reached eastern Siberia until around 4000 BCE to 3000 BCE, around the same time as the hypothesized Paleo-Eskimo migration to North America.

[5] It is also possible that some small portion of Neo-Eskimo ancestry arose from admixture with relict Paleo-Eskimos in the sub-Arctic and Arctic regions of North America, whose Dorset culture ended ca. 500 CE (the Wikipedia entries on the Thule people and Dorset culture state that some relict Dorset people were still in existence until the 1500 CE affording them far more opportunities to admix with Neo-Eskimos). Genetic identity between the Paleo-Eskimo Saqqaq culture (which arrived in Greenland ca. 2500 BCE) and the successor Paleo-Eskimo Dorset culture has been established. The Sadlermiut culture which went existing only in 1903 CE following a disease outbreak, had genetic identity with Neo-Eskimos despite using Paleo-Eskimo technologies.

[6] The Wikipedia article on the "Norton tradition" see the Choris, Norton and Ipiutak cultures as stages of the same tradition that are in continuity with each other and assigns a starting date to the Thule tradition of 700 BCE (500 years earlier than that of the Wikipedia article on the Thule people to which it links). The introductory portions of closed access Dumond (2000), which appears to be one of the leading journal articles on the topic, doesn't do much to clarify the situation, and arguably muddies the waters. Harritt (2010) adds new data and talks about a time period from 500 BCE to 0 CE for one complex of the Norton culture, but isn't exactly on point either (open access versions of this issue in honor of Dumond appear to be available here).

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The following is from the body text of the new pre-print (emphasis, headings, links and many paragraph breaks inserted editorially; citations and internal references omitted):

Executive Summary 

The new data and analyses presented in this work derive two key results on the genetic legacy of Paleo-Eskimos. First, we show that Paleo-Eskimos were very closely related to the Asian founder lineage that gave rise to Eskimo-Aleut speakers. Second, we show that Paleo-Eskimos contributed substantially to the ancestry of Native Americans speaking Na-Dene languages.  

Relationship To Previous Literature 

These results add significantly to previous studies on these topics. 

Reich et al. inferred that an unspecific Asian source contributed around 43% of the ancestry of Eskimo-Aleut speakers and around 10% of the ancestry of Chipewyans, a Northern Athabaskan-speaking population. Our analyses show that this Asian source is equivalent to the ancestral population that we here term proto-Paleo-Eskimos. We show that within this lineage, two sub-lineages formed that contributed to almost all Na-Dene speakers and to Neo-Eskimos, respectively. 

According to a different study, Northern Athabaskan speakers did not receive Paleo-Eskimo admixture, but admixture between Athabaskans and Eskimo-Aleut speakers was proposed. While we observe substantial First American ancestry in Eskimo-Aleut speakers, we find no evidence for gene flow from them into Athabaskans. Instead, we propose that the observed genetic patterns can be explained by Paleo-Eskimo ancestry in Athabaskans, as well as in other Na-Dene-speaking populations. 

Similarly, in a third study, admixture of unresolved direction between Saqqaq and ancestral Neo-Eskimos was interpreted as most likely reflecting Neo-Eskimo admixture into Paleo-Eskimos. Here we show that substantial proto-Paleo-Eskimo ancestry contributed to the founder lineage of Eskimo-Aleut speakers, and think this explains the observed admixture, as well as the presence of mitochondrial haplogroup D2a in the North Slope Iñupiat, 

Our Results 

Our results show that Paleo-Eskimo ancestry is a nearly perfect tracer-dye for speakers of Na-Dene languages including the most divergent linguistically (Tlingit) and the most geographically remote ones (Southern Athabaskans). 

It is plausible that Paleo-Eskimos rather than Neo-Eskimos contributed to Na-Dene populations in light of archaeological evidence. The arrival of Neo-Eskimos (the Birnirk and Thule cultures) into western Alaska is dated to 1,350 – 1,150 calBP, but at that point Tlingit had probably already come to occupy their current position in southeastern Alaska. It has been hypothesized that the spread of Southern Athabaskan speakers from the Subarctic was triggered by a massive volcanic ash fall 1,100 calBP. If this hypothesis is correct, both Tlingit and Apache would have had little opportunity to mix with newly arriving Neo-Eskimos, which would explain why in our analysis, southern Athabaskan speakers and Tlingit have the Paleo-Eskimo ancestry but not the Neo-Eskimo ancestry. In contrast, Paleo-Eskimo peoples lived alongside Na-Dene ancestors for millennia, providing ample opportunity for genetic interaction. Although archaeological evidence for such interaction across the coastal-interior cultural boundary remains sparse, our genetic analyses demonstrate that substantial gene flow from Paleo-Eskimos took place (25-40% in ancient Northern Athabaskans). 

When Did The First Eskimo-Aleuts Arrive? 

The time and place of the Eskimo-Aleut founder event remains uncertain. 

Under our demographic model, divergence of the lineage leading to Eskimo-Aleut speakers was dated at ~3,500 calBP, and involved gene flow from a northern First American population distantly related to Athabaskans. 

There is no clear archaeological evidence for a First American back-migration to Chukotka, so this admixture event may have occurred in North America. 

A parsimonious explanation is that the Asian ancestral population contributing to Eskimo-Aleut speakers may have remained in Chukotka after splitting from the Paleo-Eskimo lineage sensu stricto, and that members of this lineage later separated from the ancestors of Chukotko-Kamchatkan speakers and crossed the Bering Strait. 

In turn, the First American ancestral lineage that contributed to Eskimo-Aleut speakers was likely located in southwestern Alaska since the Alaskan Peninsula and Kodiak Island have long been suggested as a source of influences shaping the Neo-Eskimo material culture. The earliest maritime adaptations in Beringia and America are encountered in this region associated with the Ocean Bay tradition (~6,800 – 4,500 calBP). Early Paleo-Eskimo people used marine resources on a seasonal basis only, depended for the most part on hunting caribou and muskox, and lacked sophisticated hunting gear that allowed the later Inuit to become specialized in whaling. It is conceivable that a transfer of cultural traits and gene flow happened simultaneously. 

Place and Archaeological Culture Of First American Admixture With Paleo-Eskimos 

Where did the First American and Paleo-Eskimo-related source populations meet? 

A succession of western Alaskan cultures, namely the Old Whaling, Choris, Norton, and Ipiutak (with the earliest dates around 3,100, 2,700, 2,500, and 1,700 calBP, respectively), combined cultural influences from earlier local Paleo-Eskimo sources as well as sources in Chukotka and southwestern Alaska. Parallels between these cultures and subsequent Neo-Eskimos are notable. 

The Old Bering Sea culture, the earliest culture assigned archaeologically and genetically to Neo-Eskimos, has been dated to around 2,200 calBP and later. An individual from Uelen with the Neo-Eskimo genetic signature was dated in this study at ~1,800 calBP. 

Considering these dates, we provisionally suggest that the admixture that happened early in the history of the Neo-Eskimos may have occurred in the context of the Old Whaling, Choris, or Norton cultures, although other scenarios cannot be ruled out without further ancient DNA sampling. It is possible that Paleo-Eskimos sensu stricto may have also contributed to some lesser extent to the emergence of Neo-Eskimo peoples. 

Genetic Evidence Supports The Dene-Yeniseian Hypothesis 

The descendants of proto-Paleo-Eskimos speak widely different languages, belonging to the Chukotko-Kamchatkan, Eskimo-Aleut, and Na-Dene families. Based on lexicostatistical studies of languages surviving in the 20th century, the time depth of the former two families is likely shallow, and the Na-Dene family is probably much older, on the order of 5,000 years. Thus, the linguistic affiliation of Paleo-Eskimos is unclear. 

A Siberian linguistic connection was proposed for the Na-Dene family under the Dene-Yeniseian hypothesis. This hypothetical language macrofamily unites Na-Dene languages and Ket, the only surviving remnant of the Yeniseian family, once widespread in South and Central Siberia. 

Perhaps consistent with this hypothesis, one ancient Chukotkan sample from the Ust’-Belaya culture that was first reported in this study shows evidence of ancestry from both Paleo-Eskimos and a western Siberian group related to Kets. This genetic evidence suggests that links across geographic distances such as that between Kets and Paleo-Eskimos may have been possible. 

Although the Dene-Yeniseian macrofamily is not universally accepted among historical linguists, and correlations between linguistic and genetic histories are far from perfect, evidence of a genetic connection between Siberian and Na-Dene populations mediated by Paleo-Eskimos suggests that future research should further explore the genealogical relationships between these language families, either the closest sister-groups or those within a wider clade.