At this age they have had very little social interaction/pressure and begin to behave in very gender specific ways. To ignore biology in this case seems short sighted especially in the context of evolution and every other mammalian species on the face of the earth. I can point out the boys and girls in a litter of puppies at 4 weeks. They just behave differently.
( Again, so I don't get flamed, this is not a 100% statement because biology is distinctly individual but the tendency significantly overwhelming ).