Men and women, are we really so different? To help us understand sex, gender, and our whole place within this species, I've put together a brief timeline of how men and women have come to relate to each other. Think of it as a highlight reel of the last billion years. Enjoy.

1.2 Billion Years Ago - Sex evolves in single-cell organisms. One eukaryotic cell would approach another eukaryotic cell and tickle its membrane. If the other eukaryote tickled back, then they would open their nuclei, swap chromosomes, smoke a cigarette, and promise to call each other next weekend.

Sex evolved because combining the DNA of two organisms promoted better genetic fitness than one organism's DNA replicating itself over and over (a.k.a., genetic masturbation). As a result, sexual reproduction occurs in almost every multi-celled organism that we know of. And while there are many species of plant and fungi that have multiple sexes, almost every animal species has ended up with one male and one female.

125 Million Years Ago - Early mammals appear. Attachment and basic emotions …