Aliens do exist (at least in science fiction), but how do they reproduce? There is very little information on this score, so we just have to identify the reproduction mechanisms that evolution has selected … on Earth.
In science fiction, it is often about artificial reproduction: usually it concerns the cloning of people for the production of organs and eugenics, that is, the selection of embryos according to predetermined criteria.
Science fiction usually rarely focuses on the field or breeding of aliens. Some of the works, however, talk about intergalactic love, abductions and violent relationships.
As is often the case, aliens are a reflection of our fears and hidden fantasies. In addition, human-alien hybrids raise interesting questions in terms of species classification and evolution.
Although the reproduction cycle of some aliens has been described in great detail (for example, the biological cycles and various stages of xenomorph development in the movie "Alien"), this does not apply to most sci-fi characters. Even if the aliens are humanoid, almost nothing is usually said about their reproduction (sexually or in some other way).
Recall that on Earth, sex is not at all an integral characteristic of every species: the reproduction of most organisms (bacteria, plants, fungi, as well as flat and annelid worms) occurs vegetatively, that is, by simple cell division with a doubling of the genetic heritage of chromosomes. This type of reproduction is much simpler than sexual reproduction: only a kidney or a cutting is enough for it. Vegetative reproduction is also more effective in terms of the number of offspring.
However, it becomes an obstacle to genetic mixing, because the offspring are, in fact, clones of the original organism. The same applies to parthenogenesis: one female (often she becomes a queen) gives birth to the same offspring (males and females). This type of reproduction exists in some plants, insects and reptiles, and in most cases leads to the formation of a complex matriarchal society.
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Man and woman at the same time
Whether it's parthenogenesis or vegetative propagation, clones do occur naturally. When cloning becomes artificial, it raises concerns that in the future people may become its objects for eugenic purposes.
So, in "Star Wars" (Episode II: Attack of the Clones), the inhabitants of the planet Kamino, possessing advanced biotechnology, secretly raise and prepare an army of clones based on the genes of the most dangerous bounty hunter. A little later, the movie "The Island" describes a sterile underground community of clones: they are raised as organ donors for the rich living on the surface.
In addition, even if reproduction is sexual, it does not necessarily imply the presence of two separate sexes (male and female), as evidenced by hermaphrodites living on Earth: flowering plants (male and female genital organs, stamens and pistils, are in the same flower), as well as land (snail) and marine animals (clown fish is born a male, and then becomes a female).
Was this fish the inspiration for John Varley's Golden Globe, in which a genetically modified actor changes sex at will to play both Romeo and Juliet on his own? Intimate contact of the third degree concerns the third sex in Ayerdahl's Sexomorphosis: in this book, Emeline, who can easily change her gender, tries to find herself.
In addition, since sex serves not only for reproduction, but also for pleasure, some writers portray the hottest scenes between humans and aliens. Philip José Farmer became one of the pioneers of "erotic" science fiction: in "Lovers" (written in 1952, the story was not accepted by publishers, but was eventually published in the form of a novel in 1961), the author describes the dangerous relationship of a man who is fleeing on Earth of theocracy, and a beautiful alien (she is human in form, but insectoid in essence). Thus Farmer used sex as a weapon of social criticism in Puritan America.
Thus, the shape, type, number and ways of using the genitals depend on the worlds and species: on Earth, the genitals of insects are so different that they distinguish some species from others! On other planets everything is allowed, if, of course, the sizes of the organs are compatible with each other. When hybrids are born from these intergalactic connections, they can be perceived in completely different ways.
The Star Child, a symbol of peace in Kenneth Johnson's V (The Visitors), was the fruit of the love of a human resistance activist and a lizard from Sirius who flew to invade Earth. However, the most famous hybrid in science fiction is, of course, Spock from Star Trek, a symbol of interplanetary mixing of races and respect for others.
This son of a dugout and a Vulcan raises interesting questions in terms of phylogeny and species classification. What should you call Spock? There are no clear rules in zoology, although a combination of syllables from the names of the species of both parents is usually used. So, for example, a zebroid is a descendant of a donkey and a zebra (belong to the equidae family), a natural hybrid that Darwin observed in South Africa. Here it is necessary to clarify that the first part of the name of the hybrid is usually given by the father: for example, the tiger is a cross between a tiger (Panthera tigris) and a lioness (Panthera leo), while a liger is a descendant of a lion and a tigress.
Thus, Spock could be called a "volcano". Note also that he had a son, which means he is a hybrid capable of breeding. And this fact, in turn, says (at least from the standpoint of classical terrestrial biology) that the genes of his parents are compatible with each other. Thus, Vulcans and Earthlings belong either to the same species or to the same genus.
Suppose Homo sapiens have priority over Vulcans. In this case, all the inhabitants of Vulcan, including Spock's father, are Homo sapiens vulcanensis (if they belong to the same species) or Homo vulcanensis (if they belong to the same genus). It remains only to somehow explain the presence of the genus Homo on the planet Vulcan … Perhaps the Vulcans are genetically modified people who are adapted to life in these conditions? Or are we the Vulcans who have moved to Earth?
This thought, by the way, brings us to a much more serious hypothesis of panspermia, from which it follows that the first forms of life on Earth were of alien origin, for example, amino acids arrived from space on meteorites.
Jean-Sebastien Steyer, paleontologist at the National Center for Scientific Research
Roland Leuc, astrophysicist at the Saclay Science Center