The adult chimp has a relatively decreased frontal bossing and prominent supra-orbital ridges, and the zygomatic-maxillary-mandibular area juts out, almost like a muzzle. This is a condition called prognathism. In the baby chimp, this is barely present; it has a retrognathic facial feature compared to the adult.

In adult (and baby) humans it is the retrognathic condition that is the norm, if compared to the adult chimp. Since the baby chimp shares this condition with humans, an early theory became popular in the early 1900s. That humans are basically neotenized apes. Neoteny is the process and condition by which adults in a species retain traits seen only in the young juveniles of ancestors, or in embryos. Other such traits in baby apes or in human embryos that are retained in adult humans include a relatively large head to body ratio, relative hairlessness, reduced muscle mass, more slender skeleton, thinner bones, shorter limb to body ratio, the epicanthal eye fold (although present only in adult North East Asians, it is present in all human embryos).

That could explain why even a very slight genetic difference between a 'regular ape' and a human could result in markedly human features. All you need is a gene that would cause the retention of embryonic features.

It's an interesting question: why are humans the weak link amongst the primates when it comes to physical strength? All the other great apes are stronger than us, maybe even the lowly gibbon is stronger...

Even Neanderthals were far stronger than us. Someone worked out that a typical female could have easily outmuscled Arnie, while the males were stronger still.

There does seem to be evidence that the physical strength of the athletes in the early Olympics were much more powerful than modern athletes.

<That could explain why even a very slight genetic difference between a 'regular ape' and a human could result in markedly human features. >

I get the impression that some of the physical development part of the biological "program" may have been discarded in favor of mental development/potential.

Brain function uses up a heckuva lot of energy, so it's more "affordable" with a slighter body that requires less feeding.

<Annie K: Brain function uses up a heckuva lot of energy, so it's more "affordable" with a slighter body that requires less feeding.>

However, it still makes sense that both a bigger body AND a bigger brain does mean that in times when food got scarce, they were constantly walking the edge regarding their ability to provide sufficient sustenance for themselves. And their brains <may> have been less efficient, despite size, and particularly when underfed, which would be more often than in the case of our own, smaller, direct ancestors.

The species that did survive and become dominant expanded across even to all the continents, various islands and island groups(Hawaii for example) and population

Maybe the ability to eat just about anything was also a factor in tipping the scales. Predator/carnivores or predator/omnivores at the carnivorous end of the spectrum would be much more susceptible to the vagaries of the availability of game than vegetarian/omnivores.

Also, in the vein of "Why Big Fierce Animals Are Rare" (Paul Colinveaux), predators are comparatively sparse in terms of population, eg: big cats typically need tens of square kilometers of territory to survive let alone survive and they don't tend to wander unless forced to.

If Neanderthals were predominantly carnivorous, that could have also contributed to their death knell against the more far ranging, relatively vegetarian and competitive (niche ecologically) homo sapiens.

<Than Phan>

In hunter-gatherer societies during recurrent freezing glacials and suddenly warming interglacials, food would not be easy to come by, and any competitive advantage would probably tell after thousands of generations.

<Probably explains Oliver the "Humanzee", a chimp that lived some time ago that was touted as a human-chimp hybrid. It was eventually established that it was pure (probably neotinised) chimp>

I looked him up in you-tube and there is actually a documentary on him.

http://www.youtube.com/watch?v=-C6N...

It turns out that Wikipedia also has an article on neoteny.

The Mesozoic world's mantle and crust would also be hotter because of higher natural background radiation. That would mean more active volcanoes and earthquakes. More active volcanoes wold imply higher levels of carbon dioxide in the atmosphere as volcanoes spew out enormous amounts of CO2. More CO2, a greenhouse gas, would imply a hotter climate, all other things being equal to today's condition. Plants photosynthesize and grow faster under conditions of higher CO2, producing O2, and that would also imply higher levels of Oxygen in the atmosphere after millions of more years from the Triassic into the Jurassic. Specifically, the carbon and oxygen natural cycles would run faster with more CO2 and O2 in the atmosphere - more carbon being buried faster into the lithosphere and more CO2 being emitted from the lithosphere by volcanoes faster. More oxygen implies that larger animals could exist (dinosaurs).

<visayanbraindoctor> Very interesting link! Thanks for sharing, and instructive

<Thanh Phan: <twinlark> Thanks for clarity on the Neanderthals, from what have read before, they had makeup, music and tools to rely on also>

You're welcome, and it would have been fascinating to know their language(s)...alas that possibility would seem to reside in the realm of impossible.

<Some one ought to write a sci-fi story of a human world that has both Homo Sapiens sapiens [HSS] and Homo Sapiens neanderthalensis [HSN]. (",)>

It's almost a sub-genre, although not in the sense of full co-existence. Robert J. Sawyer wrote a trilogy of an alternative history where Neanderthals prevailed instead of HSS. Here's the wiki list: http://en.wikipedia.org/wiki/Neande... with thumbnail precis's.

<This implies that Homo Sapiens Neanderthalensis and Homo Sapiens sapiens did not significantly interbreed after the latter established viable populations in Eurasia.>

That's really interesting. I wonder what would either:

- cause interbreeding in the first place and

- cause interbreeding to stop once it started. For that level of genetic material to be incorporated into the HSS genome from the HSN, there must have been considerable interbreeding for that little while (centuries? millennia?).

<it's possible that he would have been attracted to them and mated with them,>

It was rumoured he was attracted to human women, although this may be scuttlebutt.

<the higher natural background radiation must have had some effects on nature's cycles and on the biosphere.>

Reminds me of Peter Hamilton's chapter in the Neutronium Alchemist (very highly recommended!) about how a sapient energy creature developed from an immotile life form that evolved in the extreme hot house environment of a Jovian-moon type planet. The idea of course is the extreme radiation accelerates mutations and evolution, most being unsuccessful of course, but a few evolving from primeval ooze into sapient energy creatures cruising the universe as curious wanderers, sans technology, in the space of a mere few hundred million years.

http://www.npr.org/templates/story/... - Study: Neanderthals Wore Jewelry And Makeup

http://www.metaformia.org/news-and-... - More makeup info

http://archure.net/music/neandertha... - Some compiled informations about Neanderthals

- cause interbreeding to stop once it started. For that level of genetic material to be incorporated into the HSS genome from the HSN, there must have been considerable interbreeding for that little while (centuries? millennia?).>

From what I have read, it is hypothesized that the interbreeding occurred in the Middle East just before modern humans, now carrying neanderthal genes spread all across Eurasia.

Your questions are interesting. I have to think on them.

<It was rumoured he was attracted to human women, although this may be scuttlebutt.>

The documentary in you tube claims that upon reaching teenage years, Oliver became sexually attracted to his female owner; and would try to mount her.

He never did exhibit such behavior with other female chimps. Perhaps he thought that the neotenized feature of female humans was cuter.