Over time, the human brain has evolved into an amazing organ of the human body. It can store a lot of information that is essential to the survival of the human race, and being successful in life. The brain has evolved and grown, it has always been hard to figure out what caused the growth and development. Microcephalin and the abnormal spindle-like microcephaly-associated, or ASPM, proteins are the genes that are responsible for brain size and development, and are responsible for the mutations observed in affected individuals that result in truncated gene products.
Among all of the mammals, humans have an exceptionally big brain relative to their body size. The ASPM gene is proven to be an important genetic component in the evolutionary expansion of the human brain. Evidence has shown that the ASPM gene appears to have undergone positive selection a long time ago. It is really difficult to estimate when the ASPM gene could have undergone positive selection, but it has been estimated around the time the human brain had started to expand, which was between .2 million years ago and .4 million years ago. Recent studies have shown that the ASPM gene is not undergoing positive selection right now (Zhang).
An alternative explanation for positive selection on ASPM relates to its role in the proliferation of germ cells. It has been proposed by many scientists that the ASPM gene could be under sexual selection acting on sperm development or function. However, there is no association between ASPM and relative testis size across anthropoids. There is little evidence that shows that this type of selection is possible though. It is possible that the association between the evolutionary rate of loci with brain evolution, or the evolution of traits, varies across the coding sequences with some domains having importance for specific phenotypes unaffected by evolution in other regions of the gene (Montgomery).
Since there is a lack of evidence supporting the sexual selection hypothesis by many scientists, the association between molecular evolution of ASPM both increases and decreases in mass evolution in anthropoids. This causes scientists to believe that the ASPM gene played a big role in primate brain evolution, and it also suggests that the genetic basis of brain evolution may be strongly conserved and strong developmental constraints may limit the way in which brain development can respond to selection (Montgomery).
A recent study found that the interspecies comparisons of ASPM orthologs have shown that the ASPM gene has a greater protein size, which causes the larger brain size. Since this was found, it shows how the ASPM gene has been a major factor in determining how the brain has been growing. The increase in protein size across the species is due to the increased number of IQ repeats, which suggests that the specific changes in the ASPM gene may be very influential for the evolution of the central nervous system (“Accelerated Evolution”). Since the...