Evolution and Development of the Brain

The human and mouse genomes both consist of a little over 3 billion base pairs, which produce approximately 21,000 and 23,000 genes, respectively. Interestingly, a rice plant has one order of magnitude fewer base pairs but 28,000 genes. These numbers, huge in their own right, represent the tips of enormous icebergs (search spaces). Assuming that all combinations of base pairs are possible, though many are surely lethal, a sequence of length 3 billion is a point in a space of 43,000,000,000possibilities, which is approximately equivalent to 166 followed by 1.8 billion zeros. By comparison, the estimated age of the