New thoughts during my second read of "The Origin of Species"...

Chemistree

On humans.

Every time I read this book I have new ideas and this one came to me after a second read of Darwin, and another look into the documentary "Homo Futurus". For those of you who have not seen this documentary, essentially it details that natural selection is not what drove evolution, but rather a fluctuation of the sphenoid in the base of the skull thus causing our spine to straighten and evolve to our present state. It is truly a fascinating documentary and I encourage you to watch it if you are able to find a version in english - the link I used has been deleted and I can only find it in Russian at this point in time... While I do not accept the idea that the sphenoid caused our evolutionary push forward, I think it gives insight to plausible conditions that arose over time during our evolution of natural selection.

Side note: If any of you have watched Homo Futurus, let's discuss!

Second Side Note: Before you assume I am a nazi racist, understand that this comes from a purely scientific thought.

So when I observe people of all races, there seems to be a prominent bone structure unique to that specific race that stays true over many years. The size of the bones, the shape of the skull, from what I understand they vary considerably between races. So do you think there is a parent human -let us just use the term species, species that has evolved variations over time to create the races we see today? Or perhaps that each race has their own parent species? This idea is still fresh in my mind so excuse me if I have not put this eloquently. It just seems fascinating to me... that if this be true, when one starts to breed between races one is creating a new variation of the human.


Let's discuss?

Evo

From what I've read as humans migrated, bands broke off in different areas and certain features started to become predominant among groups that interbred.

minio

The first question is how do you define race in terms of humans?

Ryan_m_b

These fluctuations (if they did occur) would have been under natural selection/sexual selection pressure.
Are you trying to ask if the different ethnicities of human evolved from different species? If so the answer is emphatically no. All the ethnicities of human we see around us are homo sapien and evolved from the same species.

Whilst not complete we have a very good understanding of the evolution of man, you may want to buy a more modern introduction to evolution book. Whilst Origin of Species is an important text it is 150 years out of date; the difference in knowledge between what Darwin new of evolution and a modern evolutionary biologist is as vast as Newton and a rocket scientist (if not more).

atyy

What about http://www.nature.com/news/2010/1004....2010.194.html? Would Africans and non-Africans count as different "ethnicities", and that due in part to different amounts of interbreeding with Neanderthals (are they a different "species" from humans?).

bobze

My thoughts exactly. Saying "well it was changes in the sphenoid", you then have to ask what drove those changes?

Natural selection is the only theory which can explain adaptive evolution. While thinking that every evolutionary change that made humans human was adaptive is incorrect, it is equally incorrect to think that a significant portion of those changes were non-adaptive.

No. Species aren't real tangible things. That is why we have so many definitions of species. The most oft used is the biological species concept, all modern humans (capable of interbreeding), are the same species.

Races are a product of local variations in allele frequencies from populations that predominantly interbred within itself. Limits to travel and accessibility to other far-away populations allows certain alleles to become more predominant.

You could, as a thought experiment, make a good argument that had the industrial revolution, globalization and world-travel never happened, some of those populations may have eventually become distinct species had they remain truly reproductively isolated. That isn't the way it turned out though and there is interbreeding that occurs through literally all human populations these days.

atyy

Ok, let me paraphrase to make sure I understand you correctly. If we define organisms as belonging to the same species if they can interbreed, then Neanderthals were not a different species from "ancient" human beings that existed at the same time, since those two groups apparently interbred.

So what is the alternative definition of species that the Nature column uses when it says Neanderthals were a different species? Also are modern humans the same species as ancient humans (the ones that coexisted with Neanderthals)?

Ryan_m_b

This is why it is a slippery thing to define, there is no such distinction in nature and our application of the term is not perfect. Getting back to Neanderthals they are actually a subspecies of Homo sapiens hence why their classified as Homo sapiens neanderthalensis

atyy

So if we use the definition suggested by bobze that species are defined by ability to breed, can the answer to the above question conceivably be "yes" - ie. does it require data to give a "no" answer, or are there no inhrently contradictory alternative hypotheses and the answer is a "no" by definition?

zoobyshoe

I picked up Origin of Species a few weeks ago and got a couple chapters into it. I haven't gotten to the part where he talks about humans, but, if it's now accepted that all humans are the same species, then his observations on pigeons might lead to interesting consequences.

He asserted that all varieties of pigeons in existence were created from the common rock pigeon, by human breeders. The way he demonstrated this was by breeding disparate varieties: one kind of pigeon with another that had vastly different characteristics. The offspring had a couple features that were common to neither parent, rather they were features of the rock pigeon. Breeding those offspring, the next generation looked even more like rock pigeons. And the next generation even more. This was against the supposition that the results would be something more and more squarely between the two parent varieties. Instead, they became more and more like rock pigeons.

So, presumably, if the same thing were done with humans, the successive generations ought to more and more clearly reveal the shape of our common ancestor. A weird and fascinating thought.

Murdstone

zoobyshoe - Found your comment stimulating. Anyone care to speculate on the genetics that would produce this result? Does it make sense to speculate that there is a dominate/recessive thing here, with interbreeding giving extra weight to the recessive?

bobze

It works for the pigeons because they've been selected (artificially) for extremes in variation. Humans, even of different races, are all very, very similar genetically (the whole "one species" thing). In other words kind of a "blend of averages" already. It wouldn't work with people.

Yes, some of those extremes in pigeon variation that the breeders bred for were likely recessive traits.

zoobyshoe

I'm not sure what you mean by this. The pigeons did not become the "average" between the the two parent varieties he chose. That's what made the results interesting. They reverted to the common ancestor of both varieties. The breeds he chose bore no resemblance to rock pigeons. The average between them wouldn't be expected to look like a rock pigeon.

bobze

I agree, that is why I put it in "". The case of the pigeons works because you are now breeding out extreme homozygosity from the two breeds. The "trick" works because these are highly selected for extreme phenotypic variation. When you start crossbreeding out that homozygosity--You get something which resembles more of an ancestral population.

You don't have that luxury with humans, because we haven't been strongly selected (AS as in an extreme case of directional selection) for extravagant variation--That is to say, there aren't "breeds" of human with extreme homozygosity. However to pull a silly example, if there were say populations of people who had artificially selected, or even if it was just because of cultural beliefs leaning on sexual selection, where people had "giant feet" and there were a similar population of people with "tiny feet"--Crossbreeding these two morphological extremes would find something more reminiscent of the ancestral populations' feet.

Apologies if my simplification made that confusing.