What factors caused us humans to have the form we have today?

[OneOnOne1162]

I was wondering about what factors caused humans to have traits and morphology different from Homo neanderthalensis and Homo heidelbergensis (our possibly closest ancestor with Homo neanderthalensis).

 

For example neanderthals have a more sloped forehead, a broader nose, are smaller, have a barrelled chest, etc. So what different conditions caused them to develop each one of these traits or what conditions caused us to develop the traits we have?

 

To give an example of the sort of anwser I might want, If my question had been about the morphology of birds with a particularly long and glorious tail like the male peacock I might expect this response:

"This is sexual dimorphism caused by female choice. Where females are the ones choosing male mates and male mates have to find ways to stand out and attract wandering females to them. This probably became the case because the resources the bird feeds on were spread equally around their habitat as opposed to being concentrated in specific areas (in which case male-male competition would've happened instead of female choice and they might've grown more muscular but without the tail)."

 

That's the sort of thing I'm looking for, except for course about the differences between Homo sapiens, Homo neanderthalensis and Homo heidelbergensis.

[OneOnOne1162]

I was wondering about what factors caused humans to have traits and morphology different from Homo neanderthalensis and Homo heidelbergensis (our possibly closest ancestor with Homo neanderthalensis).

 

For example neanderthals have a more sloped forehead, a broader nose, are smaller, have a barrelled chest, etc. So what different conditions caused them to develop each one of these traits or what conditions caused us to develop the traits we have?

 

To give an example of the sort of anwser I might want, If my question had been about the morphology of birds with a particularly long and glorious tail like the male peacock I might expect this response:

"This is sexual dimorphism caused by female choice. Where females are the ones choosing male mates and male mates have to find ways to stand out and attract wandering females to them. This probably became the case because the resources the bird feeds on were spread equally around their habitat as opposed to being concentrated in specific areas (in which case male-male competition would've happened instead of female choice and they might've grown more muscular but without the tail)."

 

That's the sort of thing I'm looking for, except for course about the differences between Homo sapiens, Homo neanderthalensis and Homo heidelbergensis.

 

So nobody has any idea? It doesn't need to be all of them at once. If you know only how one particular characteristic came to be, feel free to explain that one.

[MEC1960]

H. heidelbergensis is not much different than H neanderthalensis, except (as you point out) for some secondary characters such as a sloping forehead, pronounced brow and smaller chin in the Neanderthals. Neanderthals had more robust skeletons and musculature and had bigger brains than either heidelbergensis or sapiens. H. sapiens differs from both species by being taller and more gracile. We also have different secondary characters that are much more pronounced with comparison tot he Neanderthals but also differ with heidelbergensis such as a flatter face, more robust chin, almost no brow and a high vaulting cranium (though with a lower capacity than the Neanderthals).

 

What accounts for these differences? Since no other human species exists today we can only guess.

 

Perhaps our smaller, more gracile frame is an adaptation to a more migratory lifestyle. It does seem that our species moved around a great deal more than the Neanderthals.

 

Differences in the chin (and thus the jaw) may reflect differences in diet -there is some evidence for this.

 

Differences in the shape of the face and skull may reflect differences in the size and function of the different brains. Though Neanderthals had bigger brains it may be that their fore brain function wasn't as important to them, thus though overall their brains were bigger, their fore brains may have been smaller and this resulted in a more sloping forehead - we do not have any Neanderthal brains to know for sure. It may well be that the Neanderthal brain was better suited for a sense of smell and thus their facial structures were adapted for that; a large prognathous face may have allowed for more acute sense of smell.

 

On the other hand, some or all of these characters may be the result of sexual selection - it may be that a certain face or head shapes were preferred by either males or females (or both).

 

It's also possible that some of these differences may be mere spandrels and have no adaptive purpose.

Edited April 7, 2016 by MEC1960

[OneOnOne1162]

H. heidelbergensis is not much different than H neanderthalensis, except that (as you point out) there for some secondary characters such as a sloping forehead, pronounced brow and smaller chin in the Neanderthals. Neanderthals had more robust skeletons and musculature and had bigger brains than either heidelbergensis or sapiens. H. sapiens differs from both species by being taller and more gracile. We also have different secondary characters that are much more pronounced with comparison tot he Neanderthals but also differ with heidelbergensis such as a flatter face, more robust chin, almost no brow and a high vaulting cranium (though with a lower capacity than the Neanderthals).

 

What accounts for these differences? Since no other human species exists today we can only guess. Perhaps our smaller, more gracile frame is an adaptation to a more migratory lifestyle. It does seem that our species moved around a great deal more than the Neanderthals. Differences in the chin (and thus the jaw) may reflect differences in diet -there is some evidence for this. Differences in the shape of the face and skull may reflect differences in the size and function of the different brains. Though Neanderthals had bigger brains it may be that their fore brain function wasn't as important to them, thus though overall their brains were bigger, their fore brains may have been smaller and this resulted in a more sloping forehead - we do not have any Neanderthal brains to know for sure. It may well be that the Neanderthal brain was better suited for a sense of smell and thus their facial structures were adapted for that (a large prognathous face may have allowed for more acute sense of smell). On the other hand, some or all of these characters may be the result of sexual selection - it may be that a certain face or head shapes were preferred by either males or females (or both). It's also possible that some of these differences may be mere spandrels and have no adaptive purpose.

 

Very interesting, thank you.

[overtone]

Paul Allen, the billionaire, recently announced whose biological research he would be funding with many millions of dollars in a new venture: the criterion was the best responses to the question "What is the dark matter of biology?"

 

One of the four best responses was the question of the evolution of form - how and why organisms come to have the shapes and conformations they do, over evolutionary time. It's a dark matter problem - large, dominant, important, and largely mysterious at the moment.

 

Nobody knows, really.

[OneOnOne1162]

Paul Allen, the billionaire, recently announced whose biological research he would be funding with many millions of dollars in a new venture: the criterion was the best responses to the question "What is the dark matter of biology?"

 

One of the four best responses was the question of the evolution of form - how and why organisms come to have the shapes and conformations they do, over evolutionary time. It's a dark matter problem - large, dominant, important, and largely mysterious at the moment.

 

Nobody knows, really.

 

Well, but there must be some prevailing ideas, etc.

 

I mean for example the tail of the peacock we can be fairly sure was caused by sexual selection and female-choice.

Edited April 11, 2016 by OneOnOne1162