Sex Determination: Males are males and females are females, right?

Most students are familiar with the idea that XY individuals are destined to become male, and XX individuals are destined to become female, but Nature presents a great diversity of patterns that don’t follow this rule.
Some of these differences show up in other species, where we find sex-changers, cross-dressers, and hermaphrodites, among other things.
And even among humans, although most people clearly develop as biologically male or female, intersexual characteristics can result from a number of circumstances.
This talk explores sex determination, and how we’ve arrived at our current understanding of it.