is it true that everyone is a girl at the start but then changes into its own individual sex?

Question: is it true that everyone is a girl at the start but then changes into its own individual sex?
- Keywords:
  anatomy,
  birth,
  body,
  born,
  boy,
  gender,
  girl,
  sex
Asked by bethany123 to Rika on 23 Jun 2011.
- Chandrika Nair answered on 23 Jun 2011:
  
  well technically xx or xy is the discriminating factor so male fetuses are male from the start, however features-wise, male characteristics only develop 10 weeks in.

Question: is it true that everyone is a girl at the start but then changes into its own individual sex?