David Rap, Haaretz, News and Walla!
Direct link to this page: https://www.hayadan.org.il/spermevolution.html
The seed wars
The "kamikaze theory", which holds that the human seminal fluid contains sperms whose entire purpose is to sabotage the chances of other sperms reaching the egg and fertilizing it, probably has a special sex-appeal. It was introduced by the British biologist Robin Baker, and was also brought up in the books of the anthropologist Desmond Morris. That was about a decade ago. The public perhaps missed the stories of heroism and evil of the Second World War and the determined spermatozoa, likened to the Japanese suicide bombers, soon became a quasi-scientific fact. However, to date no evidence of such mechanisms has been found in humans.
"Sperm wars" apparently exist, but they are not necessarily waged by murderous sperm. Four months ago it was reported in the journal "Nature" about a tactic used by the grass warbler (Microtus pennsylvanicus) males, which is supposed to increase their chances of becoming fathers. When a male Nabern meets a female, a short sniff is enough for him to know if she has mated with another male before him.
In such a case, researchers from the University of Memphis in Tennessee have shown, the male will emit twice the normal amount of sperm in the female's vagina, thus increasing the likelihood of her fertilization. Even more extreme cases are known in nature, of male insects implanting in the body of females a pheromone that emits a smell that repels males; Or those who extract the sperm of their predecessors from the body of females.
Matters get complicated, of course, as the animals become more developed. In species where female sexual behavior of multiple partners is widespread, it is possible to find physiological and behavioral changes in the males, designed to increase their chances of impregnating the females despite the tough competition. In chimpanzee males, for example, large testicles have developed, capable of producing a lot of sperm. In this case the "semen war" focuses first and foremost on quantity. The need for this kind of struggle - inside the female's body - does not exist in gorillas, where "permanent" relationships are established between the dominant male and the females.
In an article published last November in the journal "Nature Genetics" a study was reported, from which it appears that sperm wars take place in some mammals (and maybe even in humans) on the genetic level. The researchers, from the University of Chicago, focused on the gene involved in the creation of semenogelin - a central protein in the seminal fluid, which is responsible, among other things, for its viscosity.
Relying on the genetic sequence found in DNA samples of 12 different primate species, the researchers determined the extent of the "development" of the gene, named SEMG2, in each species. It was found that the more significant the gene went through an evolutionary process, the more viscous the sperm of that animal was. The researchers pointed out a correlation between the degree of sperm viscosity in males and what was called, to a large extent in bad taste, the "promiscuity" of the females.
In "promiscuous" species, the males emit thick semen, which sometimes creates a physical barrier in the female's body. The increased viscosity prevents the sperm from leaking out of the female's body, but it may also be intended to prevent the sperm of other males from reaching the egg and fertilizing it.
In an interview published in the journal "Science" following the scientific article, the researchers commented that from the level of development of the gene responsible for creating semanoglin in humans, it can be concluded that the human male is "in the middle of the road" - between development that indicates faithful relationships and wild sexual behavior.
https://www.hayadan.org.il/BuildaGate4/general2/data_card.php?Cat=~~~75350591~~~37&SiteName=hayadan
