This is an interesting article www.ifs.org.uk/publications/13276
Boys and girls performance at GCSE maths and physics etc is similar. Less girls take it at a level because they are not as confident (I guess these subjects are perceived as harder) and because they dont want to be the only girl in their class at a level or uni doing these subjects.
Surely if it was genetic, it would show before they were 16?
I'm pretty sure it's never been proven that girl monkeys preferring dolls is the reason why adult human females dont work in certain environments
It's not just women that are under represented in certain industry sectors either. Ethnic minorities, overweight people, disabled people are all massively under represented in things like finance. Do your relatives think these people are genetically less able to understand science as well?
You dont have to be a psychologist to recognise that how someone is brought up, societies expectations and peer pressures etc must have a huge effect on peoples life choices.
I was one of two girls in my chemistry class at a level (didn't know the other girl at all and we were at opposite sides of the class). I got the best exam results in the class. I could never get a partner for experiments, no one wanted to double up with me, I always had to go with the teacher. It wasn't a social thing as one of these was one of my best friends and I socialised with a few of the boys outside school, and a lot of my friends were boys - I was quite a tomboy and used to play sport etc with the boys as well. They used to say they did it to wind me up. But it did mean that I always thought I was useless at the practical side of chemistry and as a result despite it being suggested by teachers I didn't study it at uni (I did other science subjects instead). I probably wasnt as great on the practical side as the theory (I'm clumsy and lose things) but in hindsight, might have made different decisions if I had been in a class with more girls or if I hadn't been treated 'differently' by the boys. I know some of the boys still (a couple went on to do chemistry degrees) and they would be absolutely horrified if they thought their 'running joke' had a lasting negative impact on me, they would not believe I didn't have the confidence to pursue it further given I used to get 100pc in most modules. And I went to a good uni and got a good science degree anyway and a resultant graduate job, so it didn't even matter...but it's easy to see situations where it could be the difference between making a decision that led to a career in law or a career in science a few years down the line
Sorry that was a bit of a ramble!