Important role of genetics for age at first sex and birth

Uppsala University

A pregnant women leaning towards a man and their hands are on her belly.

According to the new study our genes are linked with age at first sex and birth of the first child.

Photograph: Matton images

An international research team has identified hundreds of genetic variants that are linked with age at first sex and birth of the first child. The study shows that a combination of genetics, social predictors and the environment drives early or late reproductive onset and that it can be related to later life diseases.

In humans, reproduction is mainly affected by the environment and social factors, but socio- biology and genetic background are also important. The timing of first sex and child birth are essential parts of the reproductive behaviour and can be used as indicators of reproductive onset. In an international study now published in the journal Nature Human Behaviour the researchers have identified 371 genetic variants that are associated with reproductive behaviour.

“We searched the entire genome to find links between genetic variants and age at first sex and at birth of the first child. This is the largest genomic study of its kind to date and it included hundreds of thousands of individuals, both women and men. Based on our data we found that the genetic variants explained around 5-6% of the variability in the average age at sexual debut or having a first child, which is remarkably high,” says Marcel den Hoed, researcher at the Department of Immunology, Genetics and Pathology, Uppsala University.

Better later life health

The study demonstrated that it is a combination of genetics, social predictors and the environment that drives early or late reproductive onset. The researchers already knew that childhood socioeconomic circumstances or level of education were important predictors of the timing of reproduction but they now found that individuals genetically prone to postpone sex or first birth had better later life health outcomes and longevity.

The new finding that genetic factors driving reproductive behaviour related strongly to diseases such as type 2 diabetes and cardiovascular disease, may increase the knowledge about later life disease. The researchers also hope that their study can lead to a better understanding of teenage mental and sexual health, infertility and treatments to help.

Åsa Malmberg


Melinda C. Mills et al. (2021), Identification of 371 genetic variants for age at first sex and birth linked to externalising behaviour, Nature Human Behaviour. DOI: 10.1038/s41562-021-01135-3

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