Animal Family

A study performed by scientists from Iceland found that mating with a relative can significantly increase the number of children in a family. Many societies consider inbreeding unacceptable. Scientists warn that inbreeding may raise the chances of a child inheriting two copies of disease-causing recessive genes, leading to genetic disorders and higher infant mortality. Scientists found that couples formed of relatives had more children and grandchildren than unrelated couples. The study revealed that when a husband and wife were third cousins, they had an average of 4.0 children and 9.2 grandchildren. If a woman was in relationship with her eighth cousin, then the number of children declined, showing an average of 3.3 children and 7.3 grandchildren.
Size
Natalism is the belief that human reproduction is the basis for individual existence, and therefore promotes having large families. Many religions, e.g., Islam, Catholicism and Judaism, encourage their followers to procreate and have many children. In recent times, however, there has been an increasing amount of family planning and a following decrease in total fertility rate in many parts of the world, in part due to concerns of overpopulation. Many countries with population decline offer incentives for people to have large families as a means of national efforts to reverse declining populations.