Question: why dose a foetus start out as a girl?

Sarah Martin answered on 21 Jun 2012:

Hello markholmes2011!

Great question! Actually a foetus starts out as neither a girl nor a boy, until it receives the instructions from the X or Y chromosome from the father to start developing into one or the other!
But you are right – some people used to think that foetuses started off as girls simply because they don’t have penises, but there’s more to being a girl than that!

🙂 Sarah