On the nature of sex

How did sex? No answer - puzzle to be solved Science XXI century. But there is a hypothesis: according to one of them, this is a side effect of the biochemical mechanism of repair of damaged genes, which arose more than a billion years ago. Evolution proved - sex useful. Actually, we have this and so have guessed. Science has given to rational arguments
Sex appeared already in the far-celled human ancestors more than a billion years ago. Virtually all animals (with very rare exceptions) can reproduce sexually. Even at jellyfish there are male and female. Those animals which are deprived of this happiness (eg, some species of lizards), which undoubtedly had ancestors that reproduce sexually.

Why sex?

Sexual reproduction is so widespread in nature, that until the XIX century, people did not even ask why animals and plants reproduce by mating or otherwise a combination of germ cells. This question arose in the middle of the XIX century in connection with the proliferation of Charles Darwin's theories of evolution and natural selection. After all, according to this theory, so that sexual reproduction was maintained, it should help the survival of the species, and "profit" must be greater than the cost of sexual reproduction. Otherwise, the continuation of the species - including human - nature would have found something better.

Price sexual reproduction

Every action has its price. Reproduction with sex - is also very expensive. Flowering plants are forced to work, produce nectar to attract bees that carry pollen from flower to flower, helping plants carry out sexual reproduction. A male species Homo Sapiens, for example, are forced to buy interesting sports car to attract girls, girls - well, we know that "The Devil Wears Prada" ...

In addition, only half of sexually reproducing species - a female - to bear children. If the population of creatures that reproduce sexually, there was a mutant, gemmate, then ceteris paribus (eg birth, on average 2 -3 children), the descendants of this mutant can easily be replaced descendants couples sexual beings - only after 11 generations the difference in the number of offspring would be more than 1000 times (211 / 2 = 1024). Why do we still reproduces sexually? The answer to this question became clear only after the development of genetics.

From the standpoint of genetics

Charles Darwin believed that the existence of sex for the benefit of heterosis - the effect of increased survival of hybrids of different breeds of animals are often observed in animal husbandry: it is known that, say, mestizos of different breeds of horses are running faster than their "clean" relatives. But the nature, of course, the races do not care - she wondered survival of species. At the same time Charles Darwin could not explain the nature of this effect, because it was assumed that the heredity of two parents is mixed, like the blue and red paint, which results in a cross - purple paint.

Following the work of Gregor Mendel, August Weismann and other pioneers of genetics XIX century explanation of the usefulness of sex was found. According to genetics, each person carries two sets of genes: one obtained from the mother, the other - from the father. Moreover, because of the shuffling of genes in a process called crossing-over, the person receives a rather complex collection of genes from all of their grandparents. But genes sometimes accrue broken - defective. So, genetics has shown that the healthy gene, derived from the father, can cover the negative effect of the defective gene, derived from the mother, and - contrary. It became clear observation of Charles Darwin on the high survivability hybrids of different breeds of animals.

However, the persistence of mixed parentage is not the main advantage of sexual reproduction. Much more important is the possibility of a combination of several positive mutations. This phenomenon is most evident in bacteria. While the bacteria multiply by simple division, in some species, there is sex in the form of exchange of genetic material through a special hose (pilus), which the bacteria are connected with each other, as aircraft during refueling in the air. That way bacteria communicate with each other resistance genes to each newly-opened medical antibiotic. Without sex bacteria would require Millennium to consistently acquire all mutations that protect them from several antibiotics. Because of the sex they can acquire these mutations independently and then share their accomplishments.

Evolution puts on selfish

Explanations of the usefulness of sex for survival of the species considered to be sufficient until 1962, when the British zoologist VaynEdvards began to dispute about the essence of Darwinism in American biologist George Williams. Edwards thought that evolution selects species, and Williams was convinced (and failed to substantiate), that evolution selects individuals, selfish. According to Williams, a hare in the woods does not compete with the wolf, but with another hare. If one rabbit will run slightly faster than the other rabbit, it is another hare will be eaten by wolves, thus providing an evolutionary victory of the first hare.

In other words, any trait of an organism (including sex) will be assigned an evolution only if this feature is now helping a specific individual, rather than the whole of his mind in the abstract future. A large number of observations and mathematical models have confirmed the correctness of "individualist" Williams. Still further, this theory was developed by Richard Dawkins, who generally said that the true evolution of the players are not the kinds and even individuals, and genes. Body - this is only way to ensure a future for the gene.

Politically incorrect sex After the book Dawkins' "Selfish Gene" many researchers have made attempts to explain human sexual behavior as imposed on its genes optimal strategy transfer these genes into the future.

Matt Ridley, for example, showed how people evolved in small groups, living in the African savanna. In this environment, genes men prompted him to have one wife and the maximum number of mistresses. My wife - for the birth of children, which he handed over his status in the group, and a mistress - for the widest possible dissemination of their genetic material. A genetically-based strategies of women, according to Ridley, there was another - to become his wife "a reliable breadwinner" for the sustenance of children, but at the time of ovulation to try to get genes from accidentally running through a number of "pirate" with a "high quality" genes than her husband.

When people began to build cities and big states, this genetically based strategies led to the formation of societies where the majority of women have been usurped by the big bosses (kings) and specialized Don Juan. The rulers of China, the Inca Empire, Babylon had thousands of concubines - and the "beloved wife" for the transfer status. In ancient Rome, the slave-owners did not hesitate used for sexual purposes of his slaves, leaving most of the men-slaves without women.

By Ridley, these trends have led to a lot of violence and low level of cooperation among men in the ancient world. In his book, Ridley suggested that the fall of the Roman Empire in the face of Germanic barbarians were partially due precisely to the fact that the Germanic tribes existed firmly implanted monogamy, which helped the men to unite against a common enemy - in Rome.

Why is sex does not go away?

Biologist George Williams explained this way. Suppose, in a forest tree growing. It produces thousands of seeds that may fall into a variety of places - sun or shade, wet or dry. Therefore, it is important for the tree to produce various offspring - with more or less long roots, varying in height of the barrel. Descendants will compete with each other, and the most successful survive. In other words, Williams believed that sex produces a variety, in which the brothers compete with each other.

The opposite hypothesis suggested American biologist Michael Giselin. He believed that, on the contrary, Sex and the associated diversity allows the brothers to avoid competition with each other, as they begin to occupy slightly different ecological niches. For analogy, suppose that in a small village lives a family of a blacksmith. If all five children of a blacksmith inherit his craft, the four of them will die of hunger, because the country needs only one blacksmith. But if they will have different professions (weavers, carpenters), then their total income will be greater, because they will not compete for a place under the sun.

The third hypothesis suggested American biologist Leigh Van Valen. It was called "Red Queen hypothesis, named character from the works of Lewis Carroll. For the Red Queen in Carroll scamper was the only way to stay in place. According to Van Valin, sex emerged as a way of dealing with individual parasites. In the course of this struggle, there are no victories - the individual and parasites evolve at the same time, staying in one place in relation to each other because of the simultaneous "arms race".

Finally, in the last two decades, a great contribution to the clarification of the question "Why is sex" has made Russian-American biologist Alexei Kondrashov, who emigrated from Russia to the U.S. in 1991. According to the theory Kondrashov, sex in the first place need not to useful combinations of genes, and for the combination and removal of populations of harmful genes. Each of us, the representative of the species Homo Sapiens, has dozens of new mutations that were not present for our parents. Most of these mutations have no impact, some (about 1%) are harmful, a very small part is useful.

Sex, by Kondrashov, allows to collect a combination of harmful genes in a lean subgroup of individuals, then these "specially damaged" die "cleansing", as a vacuum cleaner, its population from the harmful mutations.

Getting started

Theories Williams, Giselina, Van Valin and Kondrashov explain why sex retains its usefulness, and not replaced, say, budding. Unfortunately, they do not explain how sex arose. Many hypotheses. Unknown - even more. Find the answer - the task of science of the future.