This is the sixth of a series of blogs on the subject of alien and monster biology. The first, which covers respiration, can be found here.
Reproduction can take various forms, but allows a race to produce a new generation of offspring.
Sexual reproduction in mammals occurs where two adults have sex, one carries the young and gives birth. There is usually a standard gestation period as the young mature and then the carrying parent gives birth, exposing them to the outside world.
In some animals pregnancy can go into suspended animation for months or years. This allows the creature to conceive, and then pause the pregnancy until a time of year or a resource state when the young are most likely to survive. This happens in creatures as diverse as the sea otter, wallaby, skunk, polar bear, roe deer, red panda, armadillo and various rodents and marsupials.
Could this happen in other alien species? There is no reason why not. It is postulated it could also happen in people; scientists think we still have the genes for the process, they are just turned off. In order to settle another planet, wouldn’t it be useful if your initial colonists could effectively carry a second generation, who did not immediately need resources to survive?
It is usually a female which carries the embryos or young, but does not have to be. In seahorses and pipefish, it is the male who becomes pregnant.
Genitalia can also vary vastly between races; male dragonflies have 2 sets of genitalia and have to move sperm between them in order to mate.
Other creatures lay eggs, which may be fertilised within the body, during sexual reproduction, or outside the body in a process called external fertilisation. This is used by such diverse creatures as dinosaurs, turtles, amphibians and birds.
Some species guard the nests, which is obviously more efficient for survival of the species; others leave the young to it. Many times more turtles hatch on beaches than ever make it to the sea. There are also creatures who sneak their young into other creature’s nests for protection eg cuckoos.
Eggs may have hard protective shells, such as those of birds, or softer exteriors as found in frog spawn. They all contain some food store to help the maturation and growth of the creature inside the shell.
Would alien eggs necessarily be recognised as what they are by explorers of a new environment? It is possible that they could accidentally upset a friendly species, or utterly fail to eradicate a threat species, where they had missed a life stage.
In the Storm Constantine Wraeththu, the protagonist changes gender after having sex with one of the Wraeththu. Gender changes are not that uncommon in the animal world. In clownfish, all eggs hatch as male, with one of the shoal becoming female. Another type of fish, the wrasse are all female, with the largest of the school becoming male. Should the male die, the next largest fish will become male; with this change only taking a week.
Common chemicals such as Altrazine, a weedkiller can cause sex changes in creatures, such as frogs and fish. In a recent study of 40 male African clawed frogs, kept in a solution of Altrazine, 10% of the frogs developed into females, with 2 of those 4 frogs mating with male frogs and producing male offspring. The other 2 developed ovaries, despite maintaining male DNA.
It is possible that your protagonist could have their sex changed by the atmosphere of the planet that they arrived on. Imagine the surprise if a male character unexpectedly became female and pregnant!
Some animals are hermaphrodite, meaning that the are both sexes simultaneously. This is the case with slugs which can mate as either male or female; frequently they mate simultaneously as both male and female.
Male and female creatures are not necessary for reproduction. I parthenogenesis, which is used by creatures such as snakes, sharks and amphibians, an embryo develops from an unfertilised ovum.
Poding or budding is an asexual reproduction, used by yeasts and simple creatures, where an existing individual divides into two or more new creatures. In this way, an creature can continue almost indefinitely.
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This is the fifth of a series of blog posts, which have been derived from a lecture I gave at Right on Paper, a one day conference of academic talks on various subjects, for speculative fiction writers, held in London on 3rd February 2018.
This talk, was in turn sparked by a conversation in the bar at Nine Worlds, a science fiction and fantasy convention, where I announced that there was a really interesting talk which could be given on Xenobiology and decided I’d better put my money where my mouth was.
I also blog on veterinary matters here.