Why do we walk upright?

Walking upright was probably caused by a change in environment leading to a change in behaviour that was followed by a change in bodyplan.
 
It's very simple my friend. At some point in history an alien species came to Earth, seeing that we were still walking on 4 limbs instead of 2 they chose to blend their genes with our own. In this way humans began to walk on 2 limbs not all of them, and thus was born modern man. The question comes into play, just what the purpose of this was? And how much of the DNA is still intact? What has changed, etc.
 
I can see several advantages: So you can carry a child, so you can throw a weapon, so you can run faster...

Without the need to smell for prey, we could more easily scout out animal tracks at that height...or watch for predators...
 
I believe we are the only great apes with long legs and short arms. I am told this is because we walk upright. So why do we walk upright?

For a science forum, you guys are all woefully clueless about evolution!! It's ok, I like teaching you to use your noggin!

We (humans) aren't the only great apes that walk upright- within, the past 2 million years, there have been a dozen others.

Humans just happened to outcompete them all to extinction.

Now why didn't other families of apes learn to walk upright?
Look here.

As you can see, only the genus homo resulted in upright walkers, with relativesw. This is a product of environment. Hominidae are the great apes, yet only those who live in Africa, Homininae, became terrestial. Compared to the tropical rainforests of Southeast Asia, Africa doesn't have much to support large arboreal apes. In fact, it can't. That's why there aren't any there.

The current line of thinking is that several million years ago, global climate change turned the jungles of Africa into savannah. This pushed the apes out of the forest and into the savannah- including our Homo ancestorts. They were already running around on their knuckles. The step to upright stance, which was driven by tool use, was a direct product of living an exposed life on the savannah. Groups of ancestral Homos could mob would-be predators, stoning them.

This behavior reinforced itself- groups that could use tools better, survived longer. Better tool use was associated with a more upright stance. Over time, Homos became adapted to life on the plains, while the ones in the forest stayed in the forest. Then Homo sapiens began to outcompete the other upright apes, and drove them all to extinction.

Gorillas and chimps were largely left alone, as they lived in the forest and did not compete with the plain dwelling Homo sapiens.
 
Prove it.

That Africa began losing trees before the first hominids walked upright?

Uh, alright.
Pliocene. We see the modern savannah animals in the fossil record, which would imply that the climate had changed from one that favored forest creatures, to one that favored hoofed ones. It began 5 million years ago. Recogniziable Homonids- 2.5 MYA.

This leads me to conclude that the climate change occured before humans were around to do it.

Besides the problems with time, I find it nigh impossible that pre-humans with only stony tools and the rudiments of society would be able to obliterate hundreds of thousands of sqaure miles of lowland tropical rainforest. Furthermore, why would they do it?
Slash and burn is a purely agricultural thing. Agriculture occured several orders of magnitude sooner than the paleolithic.


We did it in Australia.

Did what in Australia?
 
For a science forum, you guys are all woefully clueless about evolution!! It's ok, I like teaching you to use your noggin!

We (humans) aren't the only great apes that walk upright- within, the past 2 million years, there have been a dozen others.

Humans just happened to outcompete them all to extinction.

Now why didn't other families of apes learn to walk upright?
Look here.

As you can see, only the genus homo resulted in upright walkers, with relativesw. This is a product of environment. Hominidae are the great apes, yet only those who live in Africa, Homininae, became terrestial. Compared to the tropical rainforests of Southeast Asia, Africa doesn't have much to support large arboreal apes. In fact, it can't. That's why there aren't any there.

The current line of thinking is that several million years ago, global climate change turned the jungles of Africa into savannah. This pushed the apes out of the forest and into the savannah- including our Homo ancestorts. They were already running around on their knuckles. The step to upright stance, which was driven by tool use, was a direct product of living an exposed life on the savannah. Groups of ancestral Homos could mob would-be predators, stoning them.

This behavior reinforced itself- groups that could use tools better, survived longer. Better tool use was associated with a more upright stance. Over time, Homos became adapted to life on the plains, while the ones in the forest stayed in the forest. Then Homo sapiens began to outcompete the other upright apes, and drove them all to extinction.

Gorillas and chimps were largely left alone, as they lived in the forest and did not compete with the plain dwelling Homo sapiens.

Or it might have been as simple as, being able to walk is more sexually attractive than not being able to walk.
 
"Great Apes" is not a species, so the two are not mutually exclusive. We can be Great Apes, and ALSO be Homo sapiens. It is the distinction between Genera and Species.
Great apes are not a genus, they are the family Hominidae. There are four genera within this family: Homo (only one species), Pongo (orangutans, two species), Gorilla (two species) and Pan (chimpanzees, two species). Hominidae and Hylobatidae (gibbons or "lesser apes," 13 species in 4 genera) comprise the superfamily of apes, Hominoidea, within the order of Primates.
 
Great apes are not a genus, they are the family Hominidae. There are four genera within this family: Homo (only one species), Pongo (orangutans, two species), Gorilla (two species) and Pan (chimpanzees, two species). Hominidae and Hylobatidae (gibbons or "lesser apes," 13 species in 4 genera) comprise the superfamily of apes, Hominoidea, within the order of Primates.

The kids would say "owned". Do you want me in paper or plastic? ;)
 
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