I read this article last week about women's bodies and development. A few things struck me because I've never heard or read anything as unbiased and clearly written.
"Some aspects of shape and size, it turns out, are more closely tied to genes than others. The ease with which you develop muscle mass, for example, is a highly inherited trait. A study that appeared in the International Journal of Obesity found that while you need physical activity in order to build muscle, people who have "muscular" genes require far less exercise than others to look fit."
"But perhaps one of the biggest wild cards in determining body development is fitness. Women in their 20s and 30s who exercised as kids have less typically "feminine" body types than what was common amongst that same age-group 25 years ago. They have wider middles and narrower hips, and more muscular legs and defined arms—the result of years spent playing sports. Credit Title IX, legislature that was passed in 1972 giving girls the same athletic opportunities as boys. "Women in their thirties and early forties today are the first generation to benefit from Title IX, and many of them have bodies that look different from those of their mothers, who exercised sparingly, if at all," notes exercise physiologist Cassandra Forsythe, Ph.D., R.D. "When you build a lot of muscle as a teenager, your testosterone levels can get slightly higher, and this could contribute to a slightly wider, more boyish middle. You don't see a lot of 23-inch waists these days." Exercise also limits body fat in the hip and butt area—where women typically store flab—which explains the slimmer hips."
http://health.msn.com/health-topics/articlepage.aspx?cp-documentid=100254496&page=1