If a particular species is going to survive, then the vital function? performed by that species which are important for its survival must give a certain amount of pleasure; thus we find that human beings find pleasure in eating, pleasure in drinking, pleasure for the male in providing for his female and pleasure for the woman in looking after her man, and pleasure also in reproduction or in the act of sexual intercourse which leads to reproduction. The desire for sexual intercourse is known as libido. Libido varies from person to person, just as it varies with age, tiredness, health and the menstrual cycle.
In many respects, mating by humans obeys all the basic biological laws of the jungle. During the process of evolution different types of men and women have been produced. The basic type of male or female depends not only upon natural physical attributes but also upon mental outlook, with personality being perhaps the most dominant intrinsic sexual attribute. Thus there are females who range in femininity from the intensely feminine to those who are almost masculine; similarly, there are men who range from the intensely masculine at one extreme to the most effeminate at the other.
The intensely feminine female ought to be the ideal human reproductive machine and such a person will usually attract and also be attracted to the masculine type of male, so that by a process of natural selection at a biological level the ideal reproductive female is mated with the ideal reproductive male. This particular phenomenon is observed throughout the world whether it be in developing countries or in so-called civilized society, and although it is entirely subconscious it nearly always follows that, regardless of social class, the feminine female marries the masculine male and the less feminine female marries the less masculine male.
From a purely biological aspect the masculine type of female and the effeminate type of male arc not good vehicles for reproduction and the procreation of the human race. Nature caters for these phenomena by introducing female homosexuality, or lesbianism, which is the association of woman with woman and is partly confined to the masculine type of female. Male homosexuality is the association of man with man and is usually, but not always, confined to the effeminate type of male. Associations of this nature are, of course, reproductively sterile which is the obvious biological solution to the problem in so far as it automatically eliminates such particular human types from procreation.
Libido is under the control of hormones and, generally speaking, the greater the production of sex hormones the greater will be the libido and, therefore, the sexual desire. As people reach the age of fifty or sixty and their hormones decline in quantity so does their sexual desire or libido. The fact that libido exists as a physiological and biological function, which varies very greatly in its intensity from person to person, is sometimes overlooked by those who criticize other people because they fail to obey the restrictive conventions which are judged necessary by modern civilized society. There can be little excuse for promiscuity, but society must appreciate that it is much more difficult for some people to remain celibate than it is for others.
It nearly always follows that libido is greater amongst more feminine females than it is amongst the less feminine variety. The same argument also applies to men. It becomes, therefore, easy to understand why it is more difficult for the feminine woman, with a high libido, to obey the restrictive conventions of modern society than it is for the masculine female, who has less libido. The feminine female must exert a greater restraint in order to obey the rules of modern civilization, whereas the less feminine woman finds obedience to these laws much more easily accomplished.
Libido in the human female is dependent upon the hormone oestrogen. The action of oestrogen among lower mammals produces oestrus which is the symptom of the mating season. Oestrus may be restricted to a short time, occurring once each year (cattle, deer), or it may occur on several occasions during the year, as seen in domesticated animals and rodents such as cats, dogs, rats and mice, etc., and also in rabbits. The third type of recurrent oestrus is that found in the higher primates (humans, monkeys) in which there is an almost continuous willingness or desire to mate and this is particularly exemplified in the human female, who exhibits a monthly cycle or a recurrent oestrus which occurs thirteen times in each year. Even during the menstrual cycle, however, the libido of the average woman will vary, usually being greater immediately before and immediately after the menstrual period. Biologically it is difficult to understand why a woman should have her times of greatest libido (or oestrus) when she is least fertile, the human female being most fertile on the 14th day of a normal 28-day menstrual cycle.