According to researchers, scientists, having sons cut mothers' lives short, looking at families 250 years back. They felt that the pattern might still be seen in developing countries today. The team from Toronto looked at church records for the Sanu people, who lived in Scandinavia between the 18th and 20th centuries.
The Sanu depended on reindeer herding, fishing and hunting for their livelihood and lacked advanced medical care. On average, the reduction was 40 weeks per son, though it ranged from four to 65. Daughters increased a mother's life expectancy by an average of 30 weeks. Mothers with many daughters who survived to adulthood had the longest lifespans in these pre-industrial Sami people. A woman's longevity was not related to her total family size.
Researchers felt that boys take more of a toll on mothers than girls because they grow faster in the womb, are heavier at birth and require more care after birth. They suggested men's lifespans were not affected by the number or gender of their children because they do not suffer direct physiological costs of reproduction as women do.
Researchers wrote: Their results suggest that giving birth to sons had a higher relative long-term survival cost for mothers than giving birth to and raising daughters. Samuli Helle of the University of Turku, Finland, who led the research, there was no definite explanation for the lifespan difference and thereby suggested that girls are more likely to help with gathering food and caring for children.