In ancient China, the phenomenon of cousins marrying cousins (i.e., close relatives marrying) did exist, but this does not mean that deformed children are rare. It is true that consanguineous marriage increases the risk of genetic defects in offspring, however, there are no exact statistics on the probability of having a deformed child through inbreeding marriage in ancient times. Here's a detailed analysis on the subject:
1.Smaller sample size: In ancient times, the population was relatively small, and marriage pairings between cousins were not as common as they are in modern times. Therefore, in this case, even though the marriage of close relatives increases the risk of giving birth to deformed children, the actual number of deformed children produced may not be large, which leads to our insufficient understanding of the situation of deformed children born to inbred marriages in ancient times.
2.Genetic diversity: In ancient times, genetic diversity among people was relatively high. Due to factors such as inconvenient transportation and low population mobility, people usually choose a partner from a nearby area when choosing a mate. This helps maintain the diversity of the gene pool and reduces the risk of genetic defects due to consanguineous marriages.
3.Natural selection: In ancient times, medical technology was relatively backward, and many children with genetic defects may have died before they could grow up. In addition, due to the poor living conditions in ancient times, the child mortality rate was high, and some children with genetic defects may not be detected or counted in time. Thus, natural selection may have weakened our understanding of the ancient situation of consanguineous marriages and birth of deformed children.
4.Lack of knowledge of genetics: Ancient people lacked knowledge of genetics and did not know that consanguineous marriage could lead to an increased risk of genetic defects. This means that even if a malformed child is born, people may not attribute it to consanguineous marriage.
Although the probability of having a malformed child may have been low in the case of consanguineous marriage in ancient times, this does not mean that consanguineous marriage is harmless. Modern science has proven that consanguineous marriage increases the risk of genetic defects in offspring, such as genetic diseases, mental retardation, physical defects, etc. To reduce this risk, many countries and regions have banned consanguineous marriages.