Women (xx chromosomes) produce the estrogen hormone while men (xy chromosomes) produce the testosterone hormone. Testosterone results in greater bone density and size as well as muscle mass. On average, this means that xy chromosome males are larger.

This size difference led to females and males becoming team efforts with differing roles. Males became hunters, gatherers, and protectors due to their greater size while females became food preparers, nest builders, and nurturers to offspring.

A prominent, and likely accurate theory, of why women gravitate toward taller or larger men today is due to an instinct for survival. Thousands of years ago larger men meant more food and better protection against threats (other men or predators). On the other side of the coin, many men instinctively feel the need to protect their female partner.

While the world is very much a different place, it's likely these survival instincts live on today.