Can humans be divided ito subspecies?

Tue 7 Dec, 2021 06:53 am
Human geneticists curb use of the term ‘race’ in their papers

Field still struggles with how to accurately describe populations, study finds

Human geneticists have mostly abandoned the word “race” when describing populations in their papers, according to a new study of research published in a leading genetics journal. That’s in line with the current scientific understanding that race is a social construct, and a welcome departure from research that in the past has often conflated genetic variation and racial categories, says Vence Bonham, a social scientist at the National Human Genome Research Institute who led the study.

But alternative terms that have gained popularity, such as “ancestry” and “ethnicity,” can have ambiguous meanings or aren’t defined by genetics, suggesting researchers are still struggling to find the words to accurately describe groups delineated by their DNA, according to the study.

In the 19th and 20th centuries, many geneticists embraced the idea that there were races, such as “Negroid” or “Caucasian,” that were distinct biological groups; such “race science” helped perpetuate discrimination and inequality. (Scientists have now thoroughly demonstrated the lack of a biological basis to racial categories.)

To better understand how geneticists have used population descriptors over time, Bonham and an interdisciplinary team dove into the archives of The American Journal of Human Genetics (AJHG), which has the longest history in the field of genetics.

Editors of AJHG gave the team access to the journal’s entire archive. The researchers quantified specific terms in the full text of 11,635 articles published from 1949—the year the journal started—to 2018. They found the word “race” appeared in 22% of papers in the first decade, but its usage declined to 5% of papers in the most recent decade.

The decline in usage of “race” reflects how geneticists slowly came to understand race as “a social category with biological consequences,” the team writes in its paper, published today in AJHG.

The researchers also found that terms associated with racial groups, such as “Negro” and “Caucasian,” which were used in 21% and 12%, respectively, of papers in the first decade, started to decline after the 1970s. In the last decade, fewer than 1% of papers used those terms. This decline confirms such labels are “not based on immutable biological order but shift in tandem with social context,” the authors write.

“This paper provides a window to view the history of a society of scientists that had a big impact in how racial terminology and racial thinking was used,” says Rick Kittles, a geneticist at City of Hope National Medical Center who was not part of the study.

When “race” is used in genetics papers today, the study found, it’s more likely to be accompanied by the terms “ethnicity” or “ancestry,” perhaps because the ambiguity of the terms led researchers to simply combine them and therefore dodge their definitions. “That just means that geneticists are as confused as everyone else,” says Fatimah Jackson, a biological anthropologist at Howard University who was not part of the study.

The National Academies of Science, Engineering, and Medicine recently established a committee to produce a consensus report on the use of “race” and other terms as population descriptors in health disparities research. Other researchers are exploring how to adopt an antiracist posture in genetic publications. “One can’t be cavalier about how one describes populations,” says Bruce Korf, a geneticist at the University of Alabama, Birmingham, and editor-in-chief of AJHG. “You need to be intentional.”

“Although the paper deals specifically with the use of language, the words in many cases have deeper roots that we must face as a community,” Korf writes in an accompanying editorial. He says AJHG is updating its author guidelines and working on the phrasing of population descriptors.

To acknowledge that past geneticists helped shape the racial categories still used to discriminate today, the American Society of Human Genetics (ASHG), which publishes AJHG, yesterday announced the launch of a yearlong project to explore past injustices perpetrated through genetics, such as eugenics. Kittle, who is part of the new initiative, says it was spurred by the Black Lives Matter movement. “It’s important to recognize [ASHG’s past links to racism] in an effort to correct and provide a healing in the future,” he says. And in the next 2 days, researchers will discuss the history of eugenics in a series of talks at the National Human Genome Research Institute.

“About time,” Jackson says about ASHG’s new initiative. She hopes panelists “look into the deep historical roots and come up with alternative models that will guide us.”

“This won't be the end of it,” Jackson says. “But it’s the right direction.”

Tue 7 Dec, 2021 11:47 am
Neanderthals have contributed approximately 1-4% of the genomes of non-African modern humans, although a modern human who lived about 40,000 years ago has been found to have between 6-9% Neanderthal DNA (Fu et al 2015). The evidence we have of Neanderthal-modern human interbreeding sheds light on the expansion of modern humans out of Africa. These new discoveries refute many previous hypotheses in which anatomically modern humans replaced archaic hominins, like Neanderthals, without any interbreeding. However, even with some interbreeding between modern humans and now-extinct hominins, most of our genome still derives from Africa. Neanderthals could not have contributed to modern African peoples’ genomes because Neanderthals evolved and lived exclusively in Eurasia and therefore could not have bred with the humans living in Africa at that time.

For many years, the only evidence of human-Neanderthal hybridization existed within modern human genes. However, in 2016 researchers published a new set of Neanderthal DNA sequences from Altai Cave in Siberia, as well as from Spain and Croatia, that show evidence of human-Neanderthal interbreeding as far back as 100,000 years ago -- farther back than many previous estimates of humans’ migration out of Africa (Kuhlwilm et al 2016). Their findings are the first to show human gene flow into the Neanderthal genome as opposed to Neanderthal DNA into the human genome. This data tells us that not only were human-Neanderthal interbreeding events more frequent than previously thought, but also that an early migration of humans did in fact leave Africa before the population that survived and gave rise to all contemporary non-African modern humans.

We previously mentioned the lack of genetic contributions by Neanderthals into the modern human mtDNA gene pool. As we have shown that Neanderthal-human interbreeding did occur, why wouldn’t we find their DNA in our mtDNA as well as our nuclear DNA? There are several potential explanations for this. It is possible that there were at one point modern humans who possessed the Neanderthal mtDNA, but that their lineages died out. It is also highly possible that Neanderthals did not contribute to the mtDNA genome by virtue of the nature of human-Neanderthal admixture. While we know that humans and Neanderthals bred, we have no way of knowing what the possible social or cultural contexts for such breeding would have been.

Because mtDNA is passed down exclusively from mother to offspring, if Neanderthal males were the only ones contributing to the human genome, their contributions would not be present in the mtDNA line. It is also possible that while interbreeding between Neanderthal males and human females could have produced fertile offspring, interbreeding between Neanderthal females and modern human males might not have produced fertile offspring, which would mean that the Neanderthal mtDNA could not be passed down. Finally, it is possible that modern humans do carry at least one mtDNA lineage that Neanderthals contributed to our genome, but that we have not yet sequenced that lineage in either modern humans or in Neanderthals. Any of these explanations could underlie the lack of Neanderthal mtDNA in modern human populations.

Fast Facts:

Neanderthals have contributed between 1-4% of the DNA of humans of Eurasian descent

Neanderthals have not contributed to the genome of African modern human populations because they never lived there and could not have interbred with the ancestors of those populations

While we don’t have evidence of Neanderthal mtDNA in the modern human gene pool, there are several possible explanations for this

0 Replies
Thu 9 Dec, 2021 08:39 am
I question some of our delineations of 'species', let alone ‘subspecies'.

No doubt we could breed a ‘species' of humans with larger than average noses. Hey, if a bigger beak on a bird qualifies, why not?
Call'em homo shnozola.
0 Replies

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