The brain's 100 trillion or so interconnections provide the physical basis for its speed and sophistication.
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. But it is not the volume of growth alone that makes the production of a human brain staggering to consider. 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. The making of the human brain from the tip of a 3 millimeter neural tube is a marvel of biological engineering.
