An article was recently published in the Journal of Experimental Zoology claiming to have discovered a possible explanation for the evolutionary origin of the female orgasm. First, to quickly restate the problem: females do not need to orgasm to reproduce, and only approximately 1/3 of women orgasm during copulation. It is not as if the 2/3 of the rest of human females do not orgasm. Females have plenty of orgasms. But, the female orgasm usually involves clitoral stimulation, and unfortunately, the clitoris is just not in the right place for most sexual positions involving penile vaginal penetration. The clitoris is homologous to the penis (i.e., same genes and developmental pathways lead to both organs), so it is not surprising that clitoral stimulation leads to orgasm. The question then becomes: why does orgasm in females occur if it is not necessary for reproduction?
The authors of the Experimental Zoology article claim that the female orgasm originated in earlier species of animals in which ovulation required clitoral stimulation from the male. Their stated position is that the orgasm was subsequently retained (i.e., vestigial) along the evolutionary lineage that led to humans even though ovulation was no longer dependent on copulation. However, there is no evidence that stimulation-induced ovulation in earlier species resulted in orgasm. An orgasm is a perception of intense euphoria accompanied by gyrating muscle contractions.
The real question that should have been asked is why wouldn't females have orgasms. If there was strong selection for orgasms in males, then females would have inherited the trait as long as it did not impair their survival or reproductive success. Males have nipples for the same reason. Nipples evolved for a specific function in females, and males also have nipples because they inherited the genes and programs to build nipples from females. As long as nipples do men no harm, there is no process in evolution to prevent males from having them, so they do.
The orgasm has a very important function in the reproductive success of males. Every time a fertile man has an orgasm during intercourse, he ejaculates and there is a chance for a fertilization event. The male orgasm occurs in nearly 100 percent of the copulation events. Further, from the standpoint of evolution, the euphoria part of the orgasm is a creative solution to the problem of how to make an animal behave in ways that maximize their reproductive success. If orgasm is associated with pleasure, then by definition males will try to seek it out and in the process will fertilize females. If the male orgasm is an adaptation for motivating reproduction in males, then that means natural selection has favored genes which orchestrate the development of nerves and hormonal responses necessary to achieve an orgasm in response to specific stimulation of the penis. These genes will be inherited by female offspring as well. Why wouldn't they be?
Humans are biased in assuming the existence of a trait always must have a functional explanation. But that is not how evolution works. The female orgasm, like male nipples, are important examples to remind us that evolution produces sufficient not optimal solutions. Even though it may not make sense for females to have orgasms, because it serves no function for them or their ancestors, it still may occur as a side effect of selection on some other trait, in this case male orgasm. The mystery of the female orgasm has been thoroughly investigated already by Dr. Elisabeth Lloyd in her book, The Case of the Female Orgasm- Bias in the Science of Evolution. Bottom line, all that is necessary to understand the origin of the female orgasm is to understand the origin of the male orgasm, and that is easy, it serves a crucial function in motivating intercourse.