Is the day you lose your virginity written in your genes?

The date you first have sex or become a parent is partly down to your genes, new research has found.

But don't go blaming your parents - the unique individual circumstances you face in life play a much bigger role. 

"This is one of these studies where you wonder, did my genes make me do it?" Andrew Shelling, head of the University of Auckland's Medical Genetics Research Group, told The AM Show on Friday. 

"It was a big, huge international study where they looked at close to half-a-million people. They threw out an enormous fishing net to try and discover if anything could correlate with age at first intercourse and age at first birth… they did find some interesting things."

In total, they found 371 "interesting things" in our DNA, when it comes to age a person loses their virginity or has a baby. 

Dr Shelling said most were genes related to reproductive biology and "psychiatric characteristics", The study, published this week in the journal Nature Human Behaviour, described the latter as "externalising behaviour", which includes substance abuse disorders and attention deficit hyperactivity disorder (ADHD). 

The researchers did what they could to account for outside influences, such as education and wealth, which are known to influence the age at which people first have sex or give birth - the more, the later. 

"They did find some interesting correlations, however trying to make that into real-world sense is very hard to do," said Prof Shelling. 

He said just because you have a gene that's been linked to an outcome, doesn't make that outcome inevitable - using the AM Show cast, which includes former Blackcap cricket star Mark Richardson, as an example.

"Looking at cricketing ability, we might discover all four of us have cricketing genes but only one of us has gone on to do something about that. Same here - they found correlations to different human genes, but they may not mean anything in terms of our individual lives, depending on the families that we're from. 

"Just because they found a correlation with a gene doesn't mean to say that's going to cause us to have sex at an earlier age than anyone else."

For example, it's hard to separate from the onset of puberty, which comes a lot earlier for most than it used to.

"Hitting an early puberty of course would increase the probability of having an earlier age of sexual intercourse." 

All-up, the research found about one-fifth of the influence on the age at first intercourse or birth is influenced by our genes. 

Because the study was so huge, it turned up a few other interesting findings too - such as giving birth later in life is linked to living longer, as well as lower rates of type 2 diabetes and cardiovascular disease. The age at first birth even appeared to be just as good a predictor as education level.

"Reproductive timing thus appears to capture a latent variable that detects these metabolic effects and is a marker of a broader social trajectory that serves as a more powerful predictor of later-life disease than years of education alone," the study said. 

"This also suggests that many of the associations with diseases that have been previously ascribed to years of education may result from this more broadly defined socio-behavioural trajectory captured by [age at first birth]."