Thank you. Yes, the Princeton study is what I was trying to reference with the link in my first post, but yours is better.
Iām having trouble reconciling a lot of the discussion above with the factoid about human and chimpanzee DNA being 95% identical. (I searched a little bit before writing this, and it looks like this number came from physically pairing up half-strands of human and chimp DNA and measuring roughly how much of the strands bonded properly.)
When someone says something like:
ā¦ do they actually mean that 40% of the parts of the neanderthal genome which were different from the human genome are part of the human gene pool?
1 Like
Presumably. It gets confusing when we start throwing around percentages without defining a percentage of what.
Itās worth noting that every mammal alive today shares about 40% of its genome with every other living mammal. We can trace that shared genetic makeup back to the last common ancestor of all living mammals.
Neanderthals were much much closer to modern humans (99+ %?) than modern humans are to chimps, which is itself in the 95-99 % range, depending on how you define genetic similarity.
Added note: Keep in mind that regulator genes, which control the expression of other genes during development and later in life, play a big role in how different one species is compared to another closely related species. It might take only minor changes in a few regulator genes to make a neanderthal different from a modern human, or a human different from a chimp.
Thereās a whole new field of evolutionary-developmental biology (evo-devo) which came along long after my last genetics class, so donāt take my word for any of this!
2 Likes
No, it means āthe entire Neanderthal genomeā, as I said. We are here talking about genetic variation between populations. We all have the same genes, but not the exact same sequences of nucleotides (due to random mutations of various kinds). Over long periods of time, populations that are (to some extent) isolated from one another will accumulate different patterns of mutations in their genomes. If two isolated populations subsequently interbreed, their descendants will carry a history of such interactions in the form of population-specific genetic mutations.
It has been found that most modern human populations have a small percentage of genes (1-2% on average) that correspond to those found in the Neanderthal genome. Since it is highly unlikely that both populations accumulated the same random mutations in the same genes, it is inferred from this that they must have successfully interbred at some time during their history.
People who have Neanderthal variants of genes donāt all have the same ones. If all the different ones are taken together, they cover about 40% of the Neanderthal genome. So even though Neanderthals are extinct, modern humans still carry quite a large representative sample of their genome. However, the real interest lies in what is missing rather than what is still there. Because it is quite likely that some of the most important genetic differences between Humans and Neanderthals are to be found in the regions where there is no longer any overlap.
For a very accessible overview of the whole topic, I would highly recommend this video lecture by Svante PƤƤbo. He is undoubtably the foremost authority in this area, and is very good at explaining his subject in terms anyone can understand.
7 Likes
Ah, that makes sense. I misread the original comment.
Alpha taxonomy, the naming of species, subspecies, genera, etc., has some very clear rules. Humans are Homo sapiens because thatās the name Linnaeus gave us in the 18th-century work (10th edition of his Systema Naturae) that is considered the beginning of the zoological taxonomic system we still use and that (most importantly for us here) iNaturalist still uses. Thatās the rule.
The rules now require that any scientific name is defined by the type specimen which represents that name. Linnaeus didnāt designate type specimens, but later scientists have designated types for Linnaeusās names (and are still doing so, at least with plants). In 1959, Linnaeus was designated as the type specimen of Homo sapiens, on the grounds that he was the example of Homo sapiens that Linnaeus had studied most. Note that Linnaeus, being European, certainly had Neanderthal ancestry; Neanderthal ancestry cannot exclude one from being part of the species of which Linnaeus is not only the author but also the type specimen.
We modern humans are all one species, as indicated by our tendency to produce fertile offspring from matings both within and between all racial, geographic, national, religious, or social divisions you can think up. Therefore, we are all Homo sapiens. That is not changed by the fact that gene pool(s) from which our ancestry is drawn is more diverse than our simple ideas about evolution might suggest.
4 Likes
Aright Iāve finished watching the Svante PƤƤbo video (itās full of interesting facts, if youāre curious), and it partially resolves that particular disconnect between 40% of the Neanderthal genome being in the modern human gene-pool, while still only differing in ~1% of base pairs. The video doesnāt say explicitly, but it appears that when they saw two adjacent Neanderthal base-pair variants in an individual human, they counted the identical base-pairs between them as also having been copied from the Neanderthal genome, and that when all such segments known from modern humans are combined, about 40% of the Neanderthal genome is covered. I think this is misleading, since I was misled, but at least I (think I) understand it now.
Iām still seeing a lot of other similarly confusing statements above. (The example was just meant to be an example of a more general issue I was having; sorry for putting you on the spot, @bazwal.) E.g. some of the statements above seem to be saying things about % of genes, while others are saying things about % of all DNA (the genome), and sometimes getting them mixed up. Or possibly trying to say something much more difficult to convey briefly, like the example I happened to pick.
So Iāll just leave it with a plea to please, please, explain carefully and in full when youāre writing about cutting-edge research like this, because most people will just be silently confused and not bother to ask clarifying questions at all. So itāll be a failure to communicate, and you might not even notice. Really. This is sometimes called the Illusion of Transparency.
2 Likes
I think the simple idea that I had that led me most astray was that the taxonomic chart was something like a family tree. So I was thinking that if all modern humans have Neanderthal ancestry (referenced as a possibiliity in the article I linked at the beginning of this topic) then there would be an additional line going up to Neanderthal to indicate that ancestry, in addition to the line going up to the other early humans. I was not thinking at all about hybrids or percentages or anything like that. So all the information that Iām learning from everyone in this topic is really helping me. (I had no idea that Linnaeus is the type specimen!)
1 Like
In family tree for humans a dotted line is drawn between species, showing hybridisation, but when you create a simpe family tree you donāt show such interactions unless the hybridisation led up to emergance of a new species.
http://antropogenez.ru/tree/
2 Likes
Thank you! This is exactly what I wanted to see. And thank you for explaining the dotted lines versus the solid ones.
Thereās phylogeny (our family tree) and thereās taxonomy (how we name and classify things) and they arenāt the same, although some people cause a lot of trouble because they think they should be.
[corrected spelling to phylogeny, not phenology which is when plants reach their various life stages]
1 Like
I assume āphenologyā must be a typo - did you mean genealogy? Or perhaps phylogeny?
2 Likes
Thanks!!
2 Likes
This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.