Intelligence is not hereditary, which is evident through the Milwaukee Project. In this experiment single black mothers with an IQ of 75 or less (generally classified as mentally retarded) were given life assistance. They were given employment, and taught how to properly care for their child, in addition to having their children sent to pre-school. In these cases the IQ scores of their children averaged 100, noted as being 22 points higher than a group of children with similar parents.

The theory that "stupidity begets stupidity" only has ground in terms of the upbringing of children. If "stupid" people produce large amounts of children (often at a young age), they will be unable to properly care for a child, resulting in less intelligent offspring. It is also important to note that a person's ability as a parent is widely based off of their own parent(s), which may also result in a chain of improper parenting.

I would also generally tend to agree with the fact that ignorance can be passed down, so long as it was an active part in the raising of a child. However, ignorance does not actually relate to intelligence (as IQ tests do not measure levels of ignorance), but merely makes people unpleasant.

As such, I believe that any biological divergence of the human race is highly improbable, and I would attribute anything of the like to a cultural shift, wherein one group would become increasingly isolated and ignorant towards the world.

Yar, that's because there is an increasing birth rate, so the likely hood of people to be clever increases.