Hybridisation and how it relates to human evolution.

[Sorcerer]

With the advent of genetic evidence to suggest that Humans, Neanderthals and Denisovans have interbred and led to the world population as it is in its modern form. How likely would you consider it that there have always been many closely related species, simply geographically seperated and reunited via migration over time.

Would this be a good way to look at human evolution (and all evolution)? The aquatic ape hypothesis can be easily discounted if we accept a monoculture for speciation, but if we consider two seperate populations, one living in semi aquatic lifestyle, perhaps coastal migration, meeting up with a population adapted to savannah type living, wouldn't it be very hard to distinguish where which adaption originated.

How can we be sure that evolution is a singular branching from a common ancestor in light of this evidence. Horizontal transfer of DNA is not exclusive to hybridisation. There are many possible vectors. I know science loves Occam's Razor, but models of simplicity and reality diverge when there requires further explanation, or when the evidence points to it being untrue.

Our holobiome, could be a source for our DNA transfer, bacterio phages, plasmids, transposons. All this DNA in such close proximity could leap across to alter our germline cells.

Why is it we like to think of life as a straight branch on a tree when it is almost certainly a web?

[Ten oz]

With the advent of genetic evidence to suggest that Humans, Neanderthals and Denisovans have interbred and led to the world population as it is in its modern form. How likely would you consider it that there have always been many closely related species, simply geographically seperated and reunited via migration over time.

Would this be a good way to look at human evolution (and all evolution)? The aquatic ape hypothesis can be easily discounted if we accept a monoculture for speciation, but if we consider two seperate populations, one living in semi aquatic lifestyle, perhaps coastal migration, meeting up with a population adapted to savannah type living, wouldn't it be very hard to distinguish where which adaption originated.

How can we be sure that evolution is a singular branching from a common ancestor in light of this evidence. Horizontal transfer of DNA is not exclusive to hybridisation. There are many possible vectors. I know science loves Occam's Razor, but models of simplicity and reality diverge when there requires further explanation, or when the evidence points to it being untrue.

Our holobiome, could be a source for our DNA transfer, bacterio phages, plasmids, transposons. All this DNA in such close proximity could leap across to alter our germline cells.

Why is it we like to think of life as a straight branch on a tree when it is almost certainly a web?

Neanderthals and Denisovans DNA is not found in all modern humans. It is only found in groups of people originated in parts of Europe and Asia. I don't think it is completely accurate to imply modern humans today in general terms are hybrids.

http://news.nationalgeographic.com/news/2014/01/140129-neanderthal-genes-genetics-migration-africa-eurasian-science/

 

Furthermore Neanderthals and Denisovans were human. They did not evolve from a seperate species. They were exactly what we were only they migrated sooner. Isolation and time allowed from some different mutation. Ultimately our ability to mate implies we were all still the same species. Though the line can blur. http://evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml

 

I agree that viewing evolution as linear often doesnt work. However in the case of Neanderthals and Denisovans they are dead on gone with only trace amounts of DNA existing in segments of modern people. Modern humans also haven't evolved in any major ways in the last 60,000 years which covers the time frame of interaction with Neanderthals and Denisovans.

 

*I am not an expert. The above are merely my thoughts based on what little I know.

[chadn737]

Neanderthals and Denisovans DNA is not found in all modern humans. It is only found in groups of people originated in parts of Europe and Asia. I don't think it is completely accurate to imply modern humans today in general terms are hybrids.

http://news.nationalgeographic.com/news/2014/01/140129-neanderthal-genes-genetics-migration-africa-eurasian-science/

 

Furthermore Neanderthals and Denisovans were human. They did not evolve from a seperate species. They were exactly what we were only they migrated sooner. Isolation and time allowed from some different mutation. Ultimately our ability to mate implies we were all still the same species. Though the line can blur. http://evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml

 

I agree that viewing evolution as linear often doesnt work. However in the case of Neanderthals and Denisovans they are dead on gone with only trace amounts of DNA existing in segments of modern people. Modern humans also haven't evolved in any major ways in the last 60,000 years which covers the time frame of interaction with Neanderthals and Denisovans.

 

*I am not an expert. The above are merely my thoughts based on what little I know.

 

Neanderthals and Denisovans were quite divergent, both anatomically and genetically. The concept of a species is a loose one and ill-defined, but the fact that we interbred is not proof that they were not a different species. Besides evolution by geographic isolation is a common means of speciation.

[Ten oz]

Neanderthals and Denisovans were quite divergent, both anatomically and genetically. The concept of a species is a loose one and ill-defined, but the fact that we interbred is not proof that they were not a different species. Besides evolution by geographic isolation is a common means of speciation.

 

I agree. From the link I provided in my initial post:

"If two lineages of oak look quite different, but occasionally form hybrids with each other, should we count them as different species? There are lots of other places where the boundary of a species is blurred. Its not so surprising that these blurry places existafter all, the idea of a species is something that we humans invented for our own convenience!"

 

http://evolution.berkeley.edu/evosite/evo101/VADefiningSpecies.shtml

 

@ the OP, all modern humans do not have DNA from Neanderthals and Denisovans. Only certian populations do. So it would appear that hybridization with Neanderthals and/or Denisovans did directly impact modern human evolution.

Edited July 22, 2014 by Ten oz

[Sorcerer]

^ Did it impact Neanderthal and Denisovan evolution?

[Ten oz]

^ Did it impact Neanderthal and Denisovan evolution?

I am not sure I understand the question? We impacted them in terms of possibly causing them to go extinct but I don't think that is what you mean.

[chadn737]

^ Did it impact Neanderthal and Denisovan evolution?

 

I don't think we know that answer in terms of what the extent of introgression of Homo sapiens into these populations were. Currently we have a limited number of sequenced genomes from these other hominid species, which does not lend itself well to such a question that requires population level data.

[Anthony Morris]

Considering the small amount of DNA neandertals and denisovans left our species I feel it is safe to say that cross-breeding between Homo sapien, Homo neandertalensis and Homo denisova was not terribly successful. When similar populations breed in the wild and produce offspring that can breed in turn but do not do so very well, they are referred to as separate species. If breeding was not impaired in our ancestral hybrids, then one would expect more of their DNA to survive. I suspect that if it weren't for the fact that some of the DNA from our non-sapiens ancestors was useful in the early generations, that all of their DNA would have disappeared from our genome completely or very nearly so.

[Endy0816]

I'm honestly guessing hybridization was most likely the result of tribal warfare.

 

Was likely not an unbiased scenario for the resulting offspring to be born into.

[Anthony Morris]

Humans get together for varied reasons. Someone down on his or her luck might seek shelter and companionship with another human who is not of the same species. Love also springs from weird combos. But if two populations were having it off together a lot, one would expect to see more of their DNA and more varied forms of it if they were the same species and reproduction wasn't an issue even if this was the result of war wives or rape.