Biological evolution is a process of continuous transformation of species through changes in successive generations. It manifests as a change in allele frequencies in the population and is made possible by genetic replacement of the species in each generation of individuals. On the one hand, generates random genetic mutations and recombinations, and secondly, the needs of the environment involved on many different phenotypes appeared generation after generation, leaving only those variables of a high adaptive weight. In biology and under the laws of genetics, when the sequence of a gene in the general population exceeds 1% is not considered a random mutation, but a mutation that has been positively selected during evolution by providing an advantage to increase the chances of survival of the group.
disorder attention deficit hyperactivity disorder (ADHD) is a behavior disorder of childhood, a genetic basis, which involves many factors are causing neuropsychological disorders in children attention, impulsivity and motor overactivity. This is a generic problem of lack of control, with broad implications for their development, learning ability and social adjustment.
There are several theories to explain the symptoms of ADHD, but none of them explains the full spectrum of symptoms of the disorder. We know that ADHD is a complex disorder, in which polygenic factors play an important role in modulating the expression of the same, the combination of several of these mutations and interaction with other environmental factors, perinatal and psychosocial factors. However, despite this and the great social and economic impact of ADHD, some authors suggest that it is unclear whether this is a disorder or a common variant of human behavior (temperament).
Major advances in the study of ADHD and genetics, observed in many recent studies, led to the development both strong genetic association disorder and its permanence over time. We might ask: why children with ADHD do not decrease over time? We know that human behavioral characteristics can be selected as a trait genetically advantageous and given the high prevalence (5-10%) and extension of ADHD throughout the world, it is unlikely that a 'disorder' to be so common in humans if not has been positively selected.
The mutation of the repeat DRD4 allele 7, which is the most studied candidate gene in ADHD is the gene mutation has been described as positively selected. The architecture of the mutation, its distribution world and its prevalence in the different genres suggest that appeared as a mutation in the Upper Paleolithic and frequency has increased beyond what was expected by chance. It has been suggested that the presence of DRD4-7R, which would result in individuals with rapid response that would be selected in times of scarcity of resources in critical conditions or rapidly changing, and that this 'rapid response' of adaptation might have played a role in the exodus from Africa to Europe and Asia. There is speculation that these great changes contributed to the emergence and subsequent positive selection of DRD4-7R. This model would also help explain the current unusual geographic distribution of DRD4-7R allele, which is low in more stable populations such as Asia, but higher in populations with high migration influence in America.
The presence of this mutation DRD4-7R, therefore, is linked to exploratory behavior, increased the search for novel stimuli and risk behaviors. Throughout evolution, the behavior of ADHD has been associated with a rapid response to predators, hunting for better performance, greater capacity for mobility (more immigration), and greater reproducibility, traits that could provide a selective advantage group. The arguments that ADHD is an adaptation rely in:
- is a disorder inherited.
- is very heterogeneous and highly polygenic.
- impulsivity in ADHD is reduced in adulthood, when the cost of losing a person is maximum.
- is more common in sex with the lowest level of parental investment.
- Limited to a small minority, but common enough to be present in every geography.
- Presents a normal distribution of severity in the population.
The most accepted hypothesis of the evolutionary theory of ADHD is that it is a side effect a combination of alleles that are usually helpful, but in a certain combination or high frequency resulting in significant dysfunction in the individual. The point is that a trait that can be bad for one person may be good for the general population. For example, some people with ADHD to become criminals, but if other individuals with ADHD are bright inventors can change the course of history and enhance the employability of the population, the genes for ADHD are favored by natural selection.
The anachronism of ADHD is that apparently beneficial traits in the past, unfavorable results in today's society, what once was an adaptive response now considered a disorder. However, evolutionary theory support the concept of positive selection on populations, not individuals. . ADHD, as well as an advantage in the past for some types of societies (hunter, nomad ...), would be an advantage for the species if we accept the idea that the physical and social risk an individual may represent the group's survival.
may be that ADHD traits involve more dysfunctional now, but perhaps we should consider this approach not only when further research, but also the time to redefine what kind of education and should help to people with ADHD in the final analysis, the role of parents and educators should be to develop the potential of the child, taking into account their individual characteristics.
