Genetic hitchhiking is thought to be an inevitable result of strong positive selection in a population. The basic idea is that if a particular gene is strongly selected for (as opposed to selected against), then the chunk of the genome that carries that gene will become very common in the population.

The next post will discuss recent evidence for genetic hitchhiking in humans. So, what do we mean when we say that genes can hitchhike? To make sense of this phenomenon, we first need to review chromosomes and sexual reproduction. Most people know that sexual reproduction creates offspring that are genetically distinct from both of the their parents.

Not surprisingly, Hamlet weighed in on the nature vs. nurture question, at least once. It is certainly true that "the stamp of one defect" can wreak havoc on the scale that Hamlet describes, and whether the result is a debilitating physical limitation or damage to "the pales and forts of reason," the outcome is tragic by any measure.