It is clear that as a species, Homo sapiens exhibits a broad range of intelligences, of which heritability can account for 50 percent. The fact that there are genes which control intelligence provides a platform for evolution and natural selection to act upon. During the early development of the human race, there would have been many more challenges in finding food and reproducing than we face today, which would have made the mechanisms of natural selection much more important. In today's society, nearly anyone can survive and reproduce, which negates the principles of natural selection, which only function if there are more individuals born than a given environment can support. In essence, since we have effectively eliminated hunger and disease, we have removed any pressure from the environment to keep adapting and become more fit.
Instead, since we have removed ourselves from the "native" landscape and challenges of Africa, we have become more dependent on the psychological mechanism of general intelligence than previously in the history of mankind. While there have been definite changes in the brain that account for increased intelligence of humans over apes and other mammals such as the presence of more GABA receptors and brain growth genes, much of the intelligence that we use is partially due to environmental factors. Since we are removed from the environment in which we evolved, the gregion of the brain is forced to account for much more than it would otherwise have to. For example, if a caveman were to walk into a modern kitchen, he would have no idea what to do with anything in the room. None of the other psychological mechanisms are designed to deal with microwaves or toasters; only general intelligence is adapted to handle situations that are new and abstract.
Although thousands of years have passed since mankind migrated from Africa and populated the vast expanses of the world, there has been insufficient time for evolution to take effect and modify us to better fit our new environments.
"Some people believe that in the future we will evolve so that our brains are larger and our cognitive abilities will dramatically increase."
The chances of evolving to this level are slim because even if we were given sufficient time to let genetic changes accumulate, there is no pressure to weed out the less intelligent individuals, who actually procreate more than individuals with high IQ's (Kanazawa, 2004). Since we are now in a state of limbo where there is no evolutionary pressure, unless there is a dramatic change in the environment, or we are not able to support as many people living on the earth, I believe that the evolution of human intelligence will cease.