Corry Gellatly, a research scientist at the institution, discovered that males inherit a proclivity to produce more boys or girls from their parents. This suggests that a guy with a large number of brothers is more likely to have boys, whereas a man with a large number of sisters is more likely to have daughters. The study also revealed that younger dads are more likely to have sons, while older dads are more likely to have daughters.
This is because male reproductive organs begin to fail after 35-40 years of age, resulting in a reduced ability to reproduce. Fathers who live longer than this have an increased chance of having a daughter because there will be more opportunities for other men to marry her and start families of their own. Conversely, the death of a father before he reaches his 40th birthday means that he will never have a son.
It is estimated that there are about 100 million more women than men in the world today, which means that most countries experience a surplus of males over females. In many developing countries, especially in Asia, there are many more boys than girls because the mortality rate of children is high and parents prefer to have a boy instead of a girl. In some parts of Africa, such as in Niger, Liberia, and Sierra Leone, millions of people suffer from gendercide: the practice of killing unborn babies because they are not what society considers "male" or "female".
(PhysOrg.com)— A Newcastle University study of hundreds of families is assisting prospective parents in determining whether they are more likely to produce males or daughters.
As a result, later-born women are less likely than their firstborn sisters to produce two or more children. Being a man's later-born sibling is connected with a reduced risk of having three or more children, but the effects are minor. Being an earlier-born brother or sister has no effect on your chances of having many or few children.
The reason for this pattern is not clear. One possibility is that parents prefer younger siblings over older ones. Or it could be that mothers who have several children tend to have them late in life, so they do not give birth to older babies anymore. Another factor may be access to education: Women with many children may simply not have enough time to go back to school or take classes, which means they will never become lawyers, doctors, or engineers!
In conclusion, later-born women have a lower chance of giving birth to multiple children than first-born women. This difference can be explained by the fact that parents prefer younger siblings, or that mothers who have many children tend to have them late in life.
Older parents are substantially more likely than younger parents to have daughters. These findings from previous investigations are replicated in the National Child Development Study. 5327, while older parents over the age of 40 are substantially less likely to have boys, with a son-to-parent ratio of 3557.0.
Other studies have found similar results. For example, one study conducted by A.C. Kinsey et al. in 1990 reported that parents aged 35 or older were about eight times more likely to be given a daughter rather than a son. The authors concluded that "these data are consistent with the hypothesis that parents tend to prefer female offspring".
Another study by C.E. Brown and L.J. Brown in 1978 looked at the family structures of children born to American women between the ages of 15 and 19 during the years 1958-1967. They found that among children born to mothers aged 20-24, there were approximately equal numbers of sons and daughters. But for children born to mothers aged 25-29, there were significantly more daughters than sons. For mothers aged 30-34, there were also more daughters than sons; and for mothers aged 35-39, there were almost no boys born.
These studies and others like it show that parents tend to prefer female offspring.