Big brains and spineless penises How DNA deletions may have produced uniquely human traits.

In my chapter LESS IS MORE I suggest that loss, or deletion of working genes has been very important in human evolution. Good examples are the way in which deletion of a part of the CMAH gene, rendering it useless, had been an important, if drastic, defence against malaria back in the days of Homo erectus. The gene MYH16 appears to have been deleted at about the same time which may explain our more gracile head and jaw musculature. Now this team have winnowed through the human genome to discover over 500 deleted chunks of DNA from non-coding regions - regions that are not inside working genes. The thought is that these deletions are in regulatory parts of the genome - parts that control the ways genes express themselves - how much designated protein they make. Deletions in these areas would be like taking the brakes out of a car - and could have led to greater gene expression. They cite a deletion near the tumour suppressor gene GADD45G, for instance, that could have "removed the brakes from cell division and promoted the expansion of brain tissue". "A second deletion near the human androgen receptor gene correlates with the loss of sensory whiskers and penile spines which might have resulted in different copulatory behaviour in early humans.