Science Daily : Male Fertility Is in the Bones: First Evidence That Skeleton Plays a Role in Reproduction

Quote Originally Posted by Science Daily
Researchers at Columbia University Medical Center have discovered that the skeleton acts as a regulator of fertility in male mice through a hormone released by bone, known as osteocalcin.
The investigators then did several experiments that show that osteocalcin enhances the production of testosterone, a sex steroid hormone controlling male fertility. As they added osteocalcin to cells that, when in our body produce testosterone, its synthesis increased. Similarly, when they injected osteocalcin into male mice, circulating levels of testosterone also went up.

Conversely, when osteocalcin is not present, testosterone levels drop, which causes a decline in sperm count, the researchers found. When osteocalcin-deficient male mice were bred with normal female mice, the pairs only produced half the number of litters as did pairs with normal males, along with a decrease in the number of pups per litter.
What the article fails to mention is that osteocalcin acts on bone mineralization and calcium ion homeostasis. In other words, they strengthen both bones and teeth. High levels of osteocalcin are therefore the recipe for a strong skeleton and (large ?) strong, healthy teeth. The link with testosterone makes perfect evolutionary sense, since our male ancestors, who were hunters and warriors, needed strong muscles (developed by testosterone) and bones (built by osteocalcin). Generally speaking, strong bones are required for strong muscles lest the bone break under the muscle pressure.

The increased male fertility may be seen as a by-product of elevated testosterone. But it also explains why women favour virile men for reproduction - not just muscular ones, but those with heavy skeletons and strong jaws and teeth. It is a sure sign of higher male fertility, and we now know why.