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How human began ?

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How human began ?

Post by biologyisg8 on Sun Jan 11, 2009 8:26 pm

An article in Time Magazine about how humans began starts off with "No single, essential, difference separates human beings from other animals..." The article is mediocre, and that statement is false. To me, evolution seems to have made a very great leap from other animals to humans.

Physically though, we are pretty much related (especially genetically) to our primate ancestors, such as at the chimpanzee. However, there are certain, at present rather unexplainable, characteristics that differentiate us from all other organisms. The fact remains that we are at the "top of the heap". We have truly managed to control our environment to a very great degree. There is no other animal that has accomplished this. We are, in a sense, "the best". This itself makes us very different. Our superiority over other animals is also evident in the way we have domesticated animals and can train them to do various tasks for us. We make animals our slaves and the thing that is different about other animals is that their "spirit" (if they have any) can be broken, unlike humans. Animals have been our "slaves" for ages, but yet if ones tries to impose the same constrains on a particular group of humans, then soon enough the group will rebel (even if they are weaker) and win their freedom! History has several examples of this. For whatever reasons, lower animals do not do this. Thus we are left to assume that there is something drastically special about humans that enables us to be indignant and righteous and fight for the expression of our "free will". (Note that I mean this in the specific context of self-adaptivity---it is by no means an absolute statement that humans are generally "better" than other animals.)

The article, however, addresses the issue of how humans evolved. The theory was that the species Homo erectus (an ancestor of Homo sapiens) evolved in Africa and and took off from there about 1.8 million years ago to populate the world as we know it now. So it was a case of divergent evolution and the reason for phenotypical differences was because of the earlier humanoids adapting to different conditions. However, new evidence has turned up that indicates the presence of Homo erectus (or very close relatives) in a DIFFERENT site (namely Indonesia) more than two million years ago. This would mean that Homo sapiens evolved separately after the spread of Homo erectus and thus evolution, in this case, occured in a more convergent form.

So which theory's right? The problem is that there's very little data. A skull here, a skull there, and it forces people to come up with new theories. But even with the limited amount of evidence, and some rational thinking, we can come up with certain properties that early protohumans must have.

There is sufficient evidence to indicate that some ancestral form of humans evolved in Africa and spread out. The environmental conditions there were "perfect". Perhaps, it wasn't Homo erectus, but there had to be one link from the apes that originated from Africa. The probability of seeing two ancestral species evolve into something convergently to Homo sapiens must be taken into account. That is to say, what is the probability of seeing Homo sapiens (taking into account the present "differences") evolve twice from an ancestral species given the separation between humans now and the ancestral species? This sort of an analysis would be hard to carry out since we would have to define what "separation" is. If we do this in terms of genetic material a rigorous analysis could be carried out, but this is not possible. However, we can hypothesise the degree of genetic similarity the ancestor must have had from fossil record, and thus come up with a very rough approximation to the probability and see if it would be plausible. This probability would give a firm hold on how far apart the divergence should be in order for convergent evolution to occur.

While I would argue it was only a single line that emerged from Africa, I'd also claim that that single line meets the required probability condition to evolve into humans. But during the process of evolution of that single line itself, I don't think it's as clear cut a single transition from ape to human. Clearly, to make the great leap I mentioned above, there must've been a lot of competition between human-like species and it is this competition that enabled the leap. "There were probably many false starts and dead ends. Modern Homo sapiens was clearly not the inevitable design for an intelligent being. The species seems to have been just one several rival products---the only one successful today in the evolutionary marketplace."

And the probability condition can be softened by the fact that these ancestors could've exchanged genetic material. That is, their evolution need not have been completely convergent---they could've interbred, and this would facilitate the convergence.

So, there's a lot of room for the merging of these so-called "rival" theories. While it might be nice to have a pet theory, there is no reason to, and when contradictory evidence shows up, archaelogists and anthropologists should find a way of reconciling them instead of fighting over it.

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