Mutated sperm

Men have far more replication of their germ line cells than women. Therefore as men age they have a higher chance of mutated sperm. Women's eggs were all created 'at once' so having a child at 20 or 40 changes nothing (at least in this respect).

Since we're having kids later and later, we're accumulating more and more mutations. More and more evolution! Fuck yeah!

Meiotic Drive in Drosophila melanogaster

nature - meiotic drive.pdf

by Laurence D. Hurst and Andrew Pomiankowski

doi:10.1038/34526

Meiotic drive genes are one class of selfish gene. The best-described example is Segregation Distorter in the fruitfly Drosophila melanogaster. This is autosomal (that is, not on the X or Y chromosome) and acts in males. Males that have the driver on one chromosome but not the other have half of their sperm killed, the half that do not contain the drive gene. This, of course, is not ‘good for the individual’. But it is ‘good for the gene’, and the drive gene spreads in the population because of the increased numbers of eggs that come to be fertilized by sperm containing it. Males in which both chromosomes have Segregation Distorter are sterile. As the driver spreads, this comes to be an increasingly common occurrence. In consequence, Segregation Distorter does not eliminate the original non-driving chromosome. Although in no case is the mechanism of drive well understood, in all well-described instances the drive ‘gene’ is actually composed of two tightly linked types of gene. The simplest model proposes that one of these codes for a toxin. Even if only half of the sperm have this gene, all sperm are affected by its toxic product. — unless, that is, they contain the other gene, which codes for the antidote. Unlike the toxin, the antidote’s activity is restricted to the sperm that contain the antidote gene.