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The Development and Shaping of the Brain

ncbi.nlm.nih.gov · 6,503 words · saved by 1 readers

The making of the human brain from the tip of a 3 millimeter neural tube is a marvel of biological engineering. To arrive at the more than 100 billion neurons that are the normal complement of a newborn baby, the brain must grow at the rate of about 250,000 nerve cells per minute, on average, throughout the course of pregnancy. But it is not the volume of growth alone that makes the production of a human brain staggering to consider. The great number of functions that the brain reliably carries out and the specificity with which these are assigned to one or another type of cell or small location in the whole assembly are stunning in their complexity; yet the feat of growing a human brain occurs in hundreds of millions of individuals each year. The brain's 100 trillion or so interconnections provide the physical basis for its speed and sophistication. But how is such an intricate network constructed in the first place? Does the genetic material of the fertilized egg already contain a full set of building specifications for the human brain, in which every cell is created as a minute increment in the overall design? And if the set of instructions is indeed so closed and specific, how could chance or random mutations or the influence of the environment have played a role—as they so evidently have done and continue to do—in the emergence of the first human brains?

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