legionnaire

By far the best of the SG smilies. Such is the reason (and prodding from Irina, doineanta and others) for today's journal entry, which is about chimpanzees.

The initial question was about chimpanzees and "thiri remarkable similarity to humans." There's an easy answer to this question, but it serves as a springboard for what I consider to be an interesting discussion. Here's the answer: the reason why chimpanzees and humans are so similar is that at some point in the not so distant past, between 5 and 7 million years ago, according to most evolutionary biologists, there were no chimps nor were there any humans, but in fact a common species. Some as yet undiscovered event caused the chimps and humans to separate and become distinct from one another (the process is referred to as "speciation") to the point where they were no longer able to interbreed and produce fertile offspring, one of the requirements for being members of the same species. [RANT] If you have an issue with evolution in general and don't believe this, tough shit. The evidence is overwhelming, and it's not my job to do your homework for you - it's all out there, and denying evolution is about as accurate as claiming the earth is flat.[/RANT]

That being established, this has become a very interesting question for geneticists because the of relatively recent divergence of the two species, and the issue is timely since it was the first week in July that the fully sequenced and assembled version of the chimpanzee genome was finally released. There's little doubt that chimpanzees have lots of similarities to humans - aside from even the basic anatomical ones. Sure, we're all mammals, and our internal physiologies are more or less identical (in fact, as some of you may recall, baboon hearts have been used a few times as substitutes for humans' in organ transplants. And I understand that baboons aren't chimps, but you get my drift) Externally chimps are hairier, smaller, and their arms are proportionally longer when compared with the length of their torso. Their faces are similar but not exactly the same, as I'm sure you can attest. Their brains, however, are remarkably similar in organization, although they are roughly one third the volume of an average human brain.

With all of these remarkable similarities, it has raised the question of how, genetically and molecularly speaking, are they different from humans? Sequencing the genome was supposed to allow us to answer that question, since the human genome had already been sequenced, it would have provided a relatively straightforward basis for comparing the two sequences directly. Unfortunately, this has not turned out to be the case. While common wisdom dictates that chimpanzees are roughly 99% genetically identical to humans, the fact is that it seems to be less so. At least according to an analysis of a sizeable stretch of chromosome 21 - the two genomes were ~1.44% different with respect to single base-pair substitutions. Meaning when looking at the coding regions of genes (the part that is responsible for coding proteins, itself only around 1% of the total genome) which sounded about right. But.... in even this one region that was directly compared, which itself comprised less than 1% of the total genome of either species there were "tens of thousands" of what are called "Indels." These are insertion/deletion mutations, meaning pieces of DNA that inserted themselves into the genome, or have been deleted from the genome. Obviously these are mostly in non-coding regions of the genome (else we'd look considerably different from our distant chimpanzee cousins) but in other, less well understood areas of the DNA that are thought to be responsible for regulating both the expression levels and the localization gene products. So in fact, it would appear anyway that while we share many physiological and even behavioral similiarities, that our genetic differences are much more substantial than previously thought.

The one interesting bit of information that can be gleaned from this study is that it would appear that retroviruses (that is, viruses that integrate themselves into our genetic code, like HIV for example) seem to play a much more important role in molecular evolution than previously thought - they are believed to have been responsible for the wealth and diversity of indels in the genome. So what makes us different from a chimp could be nothing more than a bunch of highly active viruses or "transposons," which are pieces of mobile DNA that move in and out of the genome, and are considered by some to be viral precursors.

Anyway, that's about all I have to say for right now without making this too long. However, I would be happy to answer any specific questions people have (if I can, that is.)