More studies are being done on the way that mothers respond differently to male and female infants right from the start (without realising that they are doing so).

Mothers smile more at male infants than female infants was one finding that I found surprising.

I'm fairly sure that they continued to do so (unconsciously) even after being made aware of that (though don't quote me on that) ;-)

Also...

It could be the case that 99.999% of all people do x and only a very small minority do y instead. The trouble with 'experience' (compared with studies) is that some people will of course have had salient experience with that 0.001%.

As such...

The social hypothesis is still going strong.

(Of course it is genetic. It is just that environmental including social factors determine which of the genes are 'turned on' / get to be expressed as proteins. The question is really about whether the relevant genes are fairly invarient to the social differences in the way males / females are treated or whether the relevant genes are highly dependent on those social differences. With respect to hormones the same thing goes. It might be that rough and tumble play (of a very subtle variety) is an environmental cause of increased testosterone where high levels of testosterone are associated with increased violence).

Even if the mother doesn't differentially reinforce behaviour that is in synch with social stereotypes most of the rest of society does.

I don't typically see males getting excited over a new household cleaner or females getting excited over some new SUV. When baby needs a diaper change does daddy do this or is baby handed back to mummy? With respect to advertising household cleaning products and childrens toys have the greatest social role differential.

And of course there are other children who are raised very much in accordance with social roles. And children are exposed to those other children (and what those other children think of their behaviour) at daycare and school and the like...

Social nitches can be fairly robust. Gender stereotypes are changing... But fairly slowly... Fairly slowly...