I don't remember reading anything that says this explictly,
but it seems to me that that humans did not really fully understand how babies
were made, beyond the fact it took two to tango. The fact that breeding groups
were rather closely related and generally looked alike added to this. I suspect
men and women both were just as ignorant. And if there were sexual jealousies,
they were not based on any informed notion of who was or was not the father of
any particular child.
Once they started raising animals, however, and once they
started noticing the differences between one sire's offspring and that of
another, they very quickly acquired a very good seat-of-the-pants understanding
of mendelian genetics -- and selective breeding was off and running.
Once males understood they had a great deal to do with making
a baby, and just maybe, everything to do with making a baby (his seed was
planted in the 'earth' of the mother's womb), a sea-change in attitudes
developed. Men became much more concerned about ensuring the authentic paternity
of their children. A shift to patrilocalism ensues; you happily support your
brother's child, but you are reluctant to support the child of an unrelated
male.
Comments?
Mark.