Do you want a lot of healthy children? A fourth cousin or sister is the best choice!
Although it sounds quite unexpected, experts from the Icelandic biotech company deCODE genetics claim that couples with a four- and five-cousin degree of kinship on average have more children and grandchildren than other types of families.
People have long been concerned about the impact of kinship on the success of the reproductive process. Earlier studies of this issue revealed positive correlations, however, socio-economic factors (such as the traditional age of marriage and the size of families) characteristic of populations in which related marriages are common practice, such as the population of India, Pakistan and the Middle East, left a significant imprint on the biological data. The results of the new work helped specialists to understand the biological causes of the previously obtained results.
As part of the work, the authors analyzed archival data on more than 160,000 Icelandic families whose members were born in the period from 1800 to 1965. The advantages of using Icelandic data are that this population is small and is one of the most socio-economically and culturally homogeneous communities in the world. In addition, in comparison with the populations studied earlier, the population of Iceland is characterized by slight variations in the average family size, contraceptive use and marriage traditions.
For all the generations studied, the researchers obtained similar results. Women born in the period 1800-1824 and married with fourth cousins had significantly more children and grandchildren (4.04 and 9.17, respectively) than women who linked their lives with men who were at least nine cousins with them (3.34 and 7.31, respectively). This ratio was maintained for women born more than a century later, taking into account the decrease in the average number of children in the family.
Despite the general trend of the beneficial effect of kinship on reproduction, couples consisting of second cousins or having an even higher degree of kinship had fewer children. Experts explain this by the fact that children born from close relatives are characterized by lower viability due to the high probability of inheriting two copies of life-threatening recessive mutations, which often leads to fetal death before birth.
One of the evolutionary arguments in favor of related marriages is that it reduces the likelihood of miscarriage and miscarriages caused by immunological incompatibility of mother and fetus.
It is possible that the increase in the birth rate observed in the Icelandic population at the marriage of four and five cousins, on average inheriting 0.2-0.8% of the genes from a common ancestor, is a point of equilibrium in the struggle between the advantages and disadvantages of related and unrelated crossing.
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of Scientific American
13.02.2008