Does discriminatory language suggest biologists are ashamed of some of their ancestors?
Keith S. Taber
Historically, some offspring have been classed as illegitmate and so unable to claim the same rights as those recognised as legitimate children.
But are biologists treating some of our ancestors as illegitimate?
This is a bit like judges in a court of appeal announcing their decision as "the appeal is successful – the criminal is innocent".
I was listening to an old podcast recently. The first item was about how nearly all Inuits have a particular genetic variation that is adaptive to living in the Arctic with the extreme cold and restricted diet that involves. These particular genes are not unique to that group, but are only found with much lower incidence in other groups living elsewhere. These genes are in the human 'gene pool', but have been strongly selected for among Inuit communities where they are now ubiquitous.
However, what was seen as especailly interesting about this particular genetic resource was its 'origins' – from another species. These genes are considered to have arisen in Homo sapiens by transfer from another species: Denisovans.
I do not think that any present day humans have any Denisovan or Neanderthal genes
So, the claim is that modern humans have some Denisovan genes just as (according to scientific studies) we have some Neanderthal genes, and probably genes from some other archaic human species as well. Actually I argue below this is not the case, but my argument is in terms of semantics rather than being a rejection of the substantive claims.
So – spoiler alert – I do not think that any present day humans have any Denisovan or Neanderthal genes, but I am happy to accept that we may have genes acquired from other human species such as the Denisovans and Neanderthals. To explain the distinction it is useful to ask how did 'we' modern humans come to be given this genetic gift?
Who counts as an ancestor?
What I thought was of special note in this item of the episode of BBC Inside Science was the language in which it was explained. The programme description suggested:
"Can Inuit people survive the Arctic cold thanks to deep past liaisons with another species? Adam Rutherford talks to geneticist Rasmus Nielsen who says that's part of the answer. His team's research has identified a particular section of the Inuit people's genome which looks as though it originally came from a long extinct population of humans who lived in Siberia 50,000 years ago. The genes concerned are involved in physiological processes advantageous to adapting to the cold. The conclusion is that at some point, the ancestors of Inuits interbred with members of this other species of human (known as the Denisovans) before people arrived in Greenland."
https://www.bbc.co.uk/programmes/b08558n5
The expert interviewed on the episode explained:
"…what we think we can conclude now is that in fact this D.N.A. that we find in the inuits, that we think was important for them in adapting to this extreme environment, that actually was transferred to them from Denisovans or from somebody related to the Denisovans, and by transferred, how does that work, well that works by interbreeding, so in the past we know there has been some interbreeding between these Denisovans and the ancestors of modern humans, and when they interbreed of course you transfer D.N.A."
Prof. Rasmus Nielsen, University of California at Berkely
At the end of the item, the presenter reiterated:
"So, the ancestors of Inuits bred with the Denisovans, and the gift of that blessed union, were genes that helped with cold adaptation."
Dr Adam Rutherford
Now I am not a biologist, and so am perhaps I missing a nuance of how terms tend to be used in biological discourse, but all three of these statements seem to include the same logical fault.
The 'interbreeding' events being referred to are a great many generations back in time, but to ilustrate my complaint, I have prepared a much simplified diagram modelling the scenario presented in the programme, but with just a few generations:
Excluding ancestors from minority groups
Now it seems the account being presented by biology here only makes sense if we distort the usual meaning of 'ancestor'. Surely a person's ancestors are all those people who feature on direct lines of descent to that person? In my simplified figure the individual at the bottom has eight great-grandparents.1 In my understanding of 'ancestor', each of these eight people is an ancestor of the individual shown in the final generation. If that is accepted then each of the quotes above is misphrased:
- at some point, the ancestors of Inuits interbred with members of this other species of human (known as the Denisovans)
- in the past we know there has been some interbreeding between these Denisovans and the ancestors of modern humans
- the ancestors of Inuits bred with the Denisovans
Well, no. Surely what is meant here is:
- at some point, those ancestors of Inuits considered members of Homo sapiens interbred with other ancestors of Inuits who were members of this other species of human (known as the Denisovans)
- in the past we know there has been some interbreeding between these Denisovans and the other ancestors of modern humans
- the ancestors of Inuits considered members of Homo sapiens bred with the ancestors of Inuits considered Denisovans
The original statements are akin to telling someone that they are the result of their parent coupling with a communist (or: an Australian / a graphic designer / a Liverpool supporter / a goth / a sociologist, etc.), as if a communist (or sociologist, or whatever) does not deserve to be recognised as a genuine parent.
There seems to be discriminatory language here, a kind of speciesism, where only those ancesters we consider part of 'our' species count as proper ancestors, and so other kinds of human are illegitimate as ancestors.
Two types of sex: Normal sex…and something a little shameful?
This is reflected in implying that there is some abnormal type of sex going on between these different classes of humans. Normal sex is all about genetic recombination (that is, the advantage of sexual over asexual reproduction is the 'shuffling' of genes from two individuals to give different, and pretty much unique, genetic permutations in the offspring).2
But the 'interbreeding' between species is described in particular language – a 'transfer' of genes. Now, in some parts of the living world we do see a kind of transfer of genes where one organism 'donates' copies of some its genes to another organism.
That is somewhat different from breeding in human populations that relies on meiosis to produce gametes that each have half of the parental nuclear genes; and which co-contribute to a new version of the human genone when fertilisation occurs due to the fusion of two gametes – nothing is actually transferred. Like downloading a file from a website where there is not really a 'file transfer' but the copying of an orginal that remains where it was. 3
That process of sexual reproduction is what occured when two ancestors bred – regardless of whether both were Homo spaiens or one is Denisovan (or Neanderthal or some other type). So, what is meant by 'transfer' is presumably that some 'Denisovan genes' were copied into the H. sapiens gene pool.
The species question
This description would make sense if species were ontologically discrete entities. But, as Darwin (1959) long ago realised, there are not sharp, absolute distinctions between species, and biological demacractions of species are more matters of 'convenience'. If we have some 'Denisovan D.N.A.' or 'Neanderthal D.N.A.' in our genomes, then – assuming the Denisovans or Neanderthals did not have genetic engineering skills long before 'us' – then the Denisovans or Neanderthals are our ancestors.
And why not? The very logic of evolution is that if we go back far enough in time we have:
- non H. Sapiens, indeed, eventually,
- non-human,
- non-primate, even
- non-mammalian, ancestors.
Humans today may be different from Denisovans or Neanderthals, but then we are also surely somewhat different to early sapiens who had not yet got friendly enough with Denisovans or Neanderthals to have received 'transferred' genes.
So, is the language here, of transferring genetic matieral by interbreeding (contrasted with the genetic recombination occuring when speciments of H. sapiens bred), reflecting a traditonal view of species that Darwin invalidated?
That is, under the old definition, members of two different species cannot breed to provide offspring, or at least, not fertile offspring. But the Denisovans and Neanderthals that 'interbred' with our (other) ancestors and passed copies of their genes indirectly down to humans today, clearly had no trouble in that department. Nor can it be argued that these were geographically separated populations that never overlapped, and so can be considered consequently as if separate species. Clearly there must have been some degree of co-habitation between these groups to allow matings to occur.
There may be significant enough objective differences between the morphology of early Sapiens, Denisovans and Neanderthals for biologists to feel these should be considered different species, but the notion that Denisovans and Neanderthals can simply be considered as being distinct entities on other discrete branches of the evolutionary bush is challenged by the evidence that at least some of themare among our direct ancestors. Perhaps only a minority of the Denisovans and Neanderthals that shared the world with Homo sapiens have offspring alive today – but then that would likely also be true for their sapien peers.
The science teacher and philsopher Gaston Bachelard has described how science is often impeded by retaining the 'fossilised' infuence of historical ideas that science has supposedly moved on from. Is this an example? The BBC Inside Science podcast seems to be telling us we need to rethink what we mean by our ancestors, whilst using that very word without taking this into account. This is a bit like the judges in a court of appeal announcing their decision as "the appeal is successful – the criminal is innocent".
No more discriminatory language
Or, is this an example of using language loosely to communicate effectively, because being precise would lead to convoluted expressions [like my 'at some point, the ancestors of Inuits considered members of Homo sapiens interbred with other ancestors of Inuits who were members of this other species of human (known as the Denisovans)']?
Modern humans do not actually have Denisovan or Neanderthal genes, or Denisovan or Neanderthal D.N.A., but rather have some genes that are identical (or very similar) to – in effect indirect copies of – some genes of their Denisovan or Neanderthal ancestors. And no doubt those genes (or rather identical genes 4) could also be found in some of their even more distant ancestors who are in turn considered a different species again. After all, humans share many genes with many other living things, such as bananas, so references to 'human genes' or 'Denisovan genes' it is a bit like referring to characters in the Roman alphabet as 'English letters', when they are equally 'French letters' or 'Dutch letters', etcetera. They are letters that appear in English language texts, but they are not exclusive to English language texts: just as there are genes found in human genones that are not exclusive to human genones.
Referring to 'Denisovan genes' or 'Denisovan D.N.A.' speeds communication. But it has potential to mislead the non-specialist.
So, I object to any of my forebearers who happen not to be considered specimens of Homo sapiens being said to 'transfer' genes when they 'interbred' with my ancestors: they are just as much my ancestors as those partners they engaged in genetic recombination with.
So, please, no more more discriminatory language directed against some of our ancestors, just because they were in minority human groups.
Work cited:
- Bachelard, G. (1938/2002). The formation of the scientific mind. A contribution to a psychoanalysis of objective knowledge (M. McAllester Jones, Trans.). Clinamen Press.
- Darwin, C. (1859/2006). The Origin of Species.
Note:
1 In a genuine family 'tree' there are likely to be mulitple offspring from some unions, and indeed often some people will parent children with multiple partners – but this would over-complicate the diagram as it is not central to the argument being made.
In a case such as this with just four generations we would expect a person to normally have eight different great grandparents who are all unambigously three generations distant from that individual. As we consider much longer time periods it becomes increasing likely that the same ancestor occupies several (indeed, many) 'slots' on the tree (you have many fewer than 2n distinct ancestors going back n generations once n gets large) and indeed these individuals may appear in the tree across several generations.
If you are not convinced by that, please see 'Intergenerational couplings in the family: A thought experiment about ancestry'
Another way of thinking about this is that not all of your (great)n grandparents will have been alive at the same time, once n starts is more than a small number. As an extreme case, it is quite possible that the offspring of a union between a 50 year old man and a 20 year old woman (unusual but not unknown) might quite feasibly have had one pair of grandparents who died before the other grandparents were born. This is unlikely, but plausible. With each additional generation it becomes less likely that all your ancesters at that remove were alive at the same time.
2 The advantage of asexual reproduction is that the outcome should be a viable specimen in the envrionment occupied by the parent that has been cloned. Perhaps the most advanced reproducers are those species that are able to reproduce by either strategy?
3 And, just as teaching does not seek to 'transfer knowledge' from the teacher.
4 Perhaps one issue here is how we can use the term, gene, to refer both to functional sequences of nucleic acid in abstract (as we might refer to 'the carbon atom' when we mean all and any carbon atoms, not a specific one), and actual material samples. In the first sense, a parent and offspring can share the same gene; in the second sense, a copy of a parent's gene can be passed to the child. In neither sense does the 'transfer' of genes occur.
