Data from Africa reveals that menopause creates grandmothers without young children and can increase the survival chances of their daughter's kids.
In the study, scientists have tried to find what advantage giving up reproducing could have.
The scientists arrived at two hypotheses - the ordeal during childbirth is likely to kill older women, so a woman who stops conceiving after 50 has time for her last child.
The second is that the process makes a woman to help take care of her grandchildren.
Daryl Shanley and colleagues at Newcastle University, UK, studied the births and deaths of 5500 people in Gambia between 1950 and 1975 - before the advent of modern medical clinic.
The data revealed that a child, whose mother died before it was 2 years old, is ten times less likely to survive.
However, children in the age group of one and two had double the chances of surviving if their maternal grandmother was still alive.
"When menopause happened at 50, about 60 pct of children had a surviving maternal grandmother with no young children of her own, but with menopause at 65 that fell to 10 pct," New Scientist quoted Shanley, as saying.
"They had a small effect on each child's survival, but in the population as a whole that's really quite important,' Shanley said.
The effect was higher when the model believed that maternal grandmums also helped other older children survive.
The researchers also found that, if the menopause happened later, the population grew more slowly, or even diminished.
The study found that the optimum age for menopause was actually 50 years.