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Evolution of the human brain

by arunshanker
Tags: brain, evolution, human
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Dec29-13, 01:18 AM
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I should have put a smiley on my previous post ...
Dec29-13, 05:40 AM
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I should have put a smiley on my previous post ...
Forget smilies, stars dies so you could joke here today.
Dec31-13, 10:47 AM
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Truth be told, I haven't read this entire thread, but here is another take on the evolution of the human brain that many scientists don't even know about (shameless plug for my field of study hehehe).

Sialic acids are a family of very special 9 carbon sugars that cap the end of glycan structures on cellular surfaces. The most common form of sialic acid (which I'll call NeuNAc from now on) in humans is the molecule depicted below:

Animals other than humans OTOH, are capable of producing a hydroxylated form of NeuNAc called Neu5Gc (as shown below):

Many, many moons ago, humans developed a mutation in their CMAH gene (enzyme that is responsible for hydroxylation of NeuNAc), which caused humans to no longer to be able to produce Neu5Gc. In otherwords, another thing that makes us uniquely human on a molecular level is our over abundance of NeuNAc and no production of its hydroxylated form.

Ok so what? Well, outside of DNA, sialic acids have been called the most interesting molecules known to man and for good reason. Polysialic acids (PSA) is a weird post-translational modification found within the synapses of neurons on proteins called neuron cellular adhesion molecules (NCAM) (Polysialic acid is just what it sounds like--a polymer of NeuNAc). When PSA is present on NCAMs, it behaves as sort of a hydrogel that acts as a sort of anti-adhesive. It doesn't take much of a jump to see how this could be extremely important for things like neural plasticity, learning, memory, and brain development. Sialic acids are extremely important for brain function and development and are tightly regulated.

It is believed that CMAH mutated around 2.8 mya, before the human brain began developing in our ancestors 2.1-2.2 mya. Neu5Gc is specifically regulated during development in non-human animals and is tissue specific. While, Neu5Gc is found ubiquitously in adult chimp organs, Neu5Gc is specifically down regulated in the brain of chimps. So what would the effect be if you simply took away Neu5Gc expression all together (by say mutated CMAH)? Would the result be a human brain? Does this help us solve physics problems?

If this interests you, just look up Varki papers on Neu5Gc, which I don't currently have access to. He's the king of evolutionary glycobiology and explains this much better than I just did (not really my area of expertise).
Jan3-14, 09:10 PM
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Here's another version of the quote, this time from Zurek, with a very interesting twist:
"There is, however, another reason for this focus on the classical that must have played a decisive role: Our senses did not evolve for the purpose of verifying quantum mechanics. Rather, they have developed in the process in which survival of the fittest played a central role. There is no evolutionary reason for perception when nothing can be gained from prediction. And, as the predictability sieve illustrates, only quantum states that are robust in spite of decoherence, and hence, effectively classical, have predictable consequences. Indeed, classical reality can be regarded as nearly synonymous with predictability.

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