of marriage, the age of first birth, birth intervals, the age at last birth, and total fertility rate as they are natural fertility population due to their religious belief. The Dogon population in Mali, West Africa are a natural fertility population with high fertility rate and they have been studied to understand the role of the age of wife, the age of husband, nutritional status, breastfeeding status, sex of last child, economic status, and polygyny on the waiting time to conception. Natural fertility population in rural Bangladesh have been studied to predict the role of parity, pregnancy loss, mother's age, economic status, child's sex, and husband's migration on the distribution of postpartum amenorrhea. Quality-quantity trade-offs in fertility The number of children in any family is associated with the quality of those children. There is a trade-off between reproduction and survival of the children which influence total fertility rate in humans globally> In sub-Saharan African countries, child survival is negatively associated with the number of children in the family due to the child competition for parental investment. The decrease in birth interval rate can also endanger the life of the child. In the Hungarian population, a shorter birth interval is associated with less investment of the mothers which results in small body size and low birth weight of the children at birth. In historical Ireland (1700-1919) the number of children in the family was negatively associated with the lifespan and reproductive success of the children. In various natural fertility populations, the shorter birth interval length may cause higher deaths of the infants. The hunter-gatherer !Kung mothers require to carry a greater amount of food and baby on foraging trips and shorter birth interval length results higher infant mortality among them. The 4-year birth interval is the optimum for the !kung women to have a maximized reproductive success. The total fertility of the women is also related to the post-reproductive survival of the women and in pre-industrial (1766-1895) Swedish population, the number of children was found be to be negatively associated with the longevity of the mothers. Physiology and maturation Puberty is the transitory stage in human development in which a person goes from a child into a reproductively mature adult, in other words, puberty is the process of sexual maturation in humans. The onset of puberty varies between boys and girls, with boys usually starting around 11–12 years of age and