A double-blind, placebo-controlled study investigating the anti-aging properties of collagen conducted by the University of Kiel’s Department of Dermatology found that —5 grams of collagen hydrolysate used among women aged 35–55 once daily for eight weeks supports skin elasticity, skin moisture, transepidermal water loss (dryness) and skin roughness. At the end of only four weeks, those using collagen showed a statistically significant improvement in comparison to those using a placebo with regard to skin moisture and skin evaporation, plus noticeable decreases in signs of accelerated aging. ( 8 )
The second theory is similar and is known as "evolutionary neuroandrogenic (ENA) theory of male aggression".   Testosterone and other androgens have evolved to masculinize a brain in order to be competitive even to the point of risking harm to the person and others. By doing so, individuals with masculinized brains as a result of pre-natal and adult life testosterone and androgens enhance their resource acquiring abilities in order to survive, attract and copulate with mates as much as possible.  The masculinization of the brain is not just mediated by testosterone levels at the adult stage, but also testosterone exposure in the womb as a fetus. Higher pre-natal testosterone indicated by a low digit ratio as well as adult testosterone levels increased risk of fouls or aggression among male players in a soccer game.  Studies have also found higher pre-natal testosterone or lower digit ratio to be correlated with higher aggression in males.     
Freemartins are occasionally used in stem cell and immunology research.  During fetal development cells are exchanged between the fused circulations of the bovine twins. Up to 95% of the freemartin's blood cells can be derived from those of her twin brother. Male-derived cells and their progeny can be easily visualized in the freemartin tissues, as only they contain the male Y chromosome . Thus, by analyzing these tissues, one can investigate the capacity of hematopoietic stem cells or other circulating cells to produce other tissues in addition to blood. The freemartin model allows one to analyze perfectly healthy and unmanipulated animals, without resorting to transplantation often used in stem cell research.