Simon, while I agree men and women share more similarities than differences, many differences are WAYYYY bigger than your - cherry picked - butt example. What about...

- Breasts

- Genitals

- Reproductive system

- Endocrine system (glands and hormones)

- Muscles

- Attitude towards sex (men: all the time; women: eh, it depends...)

- Attitude towards romance (the opposite of above)

- Attitude towards risk and danger...

When you consider such aspects, differences are meaningful or huge, and it looks like really men and women come from different planets.

So... come on, using just butts to support your thesis is, at least, intellectually dishonest! ;-P

(and I'm sure you know it... but you wanted to support your bias anyway)