One of the things that happened in the course of doing science is that I began to understand more about me. Me as a male. This is because when I was studying a group of coral reef snails belonging to the genus Oliva or olive snails, I discovered interesting things about their penises.
The penis is what allows a male to inseminate a female. A penis is a muscular organ, capable of contracting and relaxing. Some species have males with penis like structures, capable of penetrating the female, but since they aren't muscular they aren't penises. An example is the gonopodium of a male guppy.
The male animal has to rise to the occasion, that is the penis must remain erect at least until sperm is delivered to the female. And this is no joking matter. Male olives spend a lot of energy in getting their proportionally large penises ready for a night of sex under the coral sand.
Despite my best efforts, I couldn't find an erect Oliva penis in the field. I spend moonlit nights on reef flats trying to observe the molluscan tryst and act of life. Too bad. They do it right under the cover of sand. Copulation on sand is so common among marine snails. I have seen murexes extend their penises many times.
But in studying preserved Olivas in a Florida museum, I opened a bottle with two Olivas fixed in alcohol. The two were unfortunately collected by dredging just when the male had his penis inserted into the female's vagina. They were immediately fixed in as if in eternal frozen ecstasy. I was elated and depressed at the same time. Elated since I have proof about how his proportionally huge penis can be erect and inserted in the vagina. Depressed since who would want to be fixed in alcohol during sex?
One thing is sure. Erections are energy intensive. One thing is doubly sure. Males like me and the murexes and olives know that rising to the occasion is a direct cue of intent to have sex. The problem is that females don't get it all the time. And my brothers in evolution, Olivas, fiddler crabs, cocks, bulls, crocodiles, praying male mantises, black grooms of soon to be black widow spiders etc have to invest more in order to get a female to have sex with us. In the case of the latter two, the male has to offer 100% of himself, head, body, hemocoel (insect blood), sperm, soul and life. This energetic union between male and female is literally two becoming one flesh. It is a wonder that religion and culture did not make these two the icons of marriage!
In vertebrates the physiology of sexual arousal has been well studied. In non-human primates erections do not just advertise sexual intent but a general interest in social interaction. In non-human hominids erections have a larger social function. It is a cue to females that the male can and does intend to invest time and energy in reproduction and beyond, like raising a family and even more beyond in some species, monogamy.
In males of many species, we need a cue to achieve erection. For my male Oliva snails, it's likely a pheromone and an olfactory cue. For chimps, gorillas and my brother Homo sapiens males, we need a visual cue.
Farmers have known for thousand of years what cues are needed to initiate stud bulls to do what they are required to do. It was in animal husbandry that the study of male libido started.
Obviously testosterone and the testicles have something to do with it. Is libido the result of testosterone levels or is it the other way around? In 1970 an anonymous field biologist was living alone on an island in the Atlantic. During his regular forays to a nearby inhabited island for supplies and sex, he measured the growth of his beard on his lonely island and when he was to visit the inhabited island. In anticipation for the chance to have sex, the growth rate of his beard became faster.
This study is the first in science to document human libido, testosterone and a secondary sex characteristic in the field. The unknown researcher detailed his sexual responses such as the nature of his erections. As all men know there are times when we are tired or inebriated, we can't get it so hard.
But caveats need to be taken. His situation is atypical of human males. Most human males cohabit with human females in a largely monogamous arrangement. Now no one has made a similar study on cohabiting males with females.
I have many married men among my friends and this libido thing is a butt of ribald jokes when no females are present amongst us. It is often implied in these jokes monogamy depresses libido! Well females really don't get it all the time. That is the wisdom of Darwinian sexual selection!
Too bad I am a bachelor male and lacks that kind of experience. Although I know how it is to be celibate for long periods and heterosexually active at times, I never made an attempt to look into myself being a man until I studied male Olivas. I can't even relate if my hair loss is due to increasing or decreasing libido.
Or maybe it's time for me to get married?!