Feeling sexy? It could be the testosterone

The testicles are located outside of the body where the sun doesn’t shine and they’re responsible for releasing testosterone. Testosterone aids in the growth of facial hair, deepening of voice and growth in boys when they hit puberty. (Ovaries and adrenal glands also produce testosterone at lower levels in girls and women.) Fun fact: The testes are about two degrees cooler than the rest of the body, as lower temps are better for sperm production.

We’ve tried a lot of strange experiments with those dangly doodads. The first ever experiment with hormones happened in 1848 when German researcher Arnold Berthold testicle-swapped his roosters — reinserting some on bellies or taking a testicle from one rooster and implanting it into another one. He found that no matter where you put the testicles, there was an effect: Those without testes got fat, lazy and less interested in sex, while those who were packing tummy testes saw the opposite effect.

Other (similarly bizarre) experiments followed. In one, the researcher removed male rat testicles and watched the rats “wither.” Then he inserted the testicles into the rats’ bellies and voila! The rats’ energy increased and their sex drive surged, writes Epstein. The researcher also removed ovaries from female rats and attached testicles to their bellies and found that the rats had grown “a large clitoris, coarse hair and behave[d] exactly like a normal male,” Epstein writes.

Over a man’s life, there is a considerable drop in the production of testosterone. Starting at age 30, a man’s testosterone drops by 1 percent a year. “It’s a slow leak, like a tiny hole in a bike tire that may not be noticeable until the tire is nearly flat.” This may explain young men’s obsession with Air Jordans and other “cool” clothing brands. According to a 2018 study by Nature magazine, giving men more testosterone makes them prefer high-status items.