Want a crunchy fact for your sci-fi novel? A little something that gives a sense of place, science, or culture?
How about this: your extraterrestrials always give birth to twins.
In humans twin births are rare, happening about 4 times to 1,000 births, but get this: Clawed New World monkeys (Callitrichidae) — tiny wee creatures between 4 to 21 ounces – rarely have one baby, instead they nearly always have fraternal twins (or triplets when in captivity) and they can do so with greater ease than humans in part because they develop their placenta a lot longer than we do – meaning there's more nourishment there to support the babies as they grow.
So right there's a crunchy fact your xenobiologist can share for why this alien race seems to be able to produce so many twin and triplets.
But wait, there's more!
Nine-banded armadillos give birth to four identical pups at a time and here's your crunchy fact: some think one reason may be so the animals can't interbreed, meaning they must leave the nest to find a mate.
Side fact: while only one dog is known to have given birth to twins, some vets think it might be a bit more common than thought.
Next time: why there's no such thing as a cold, dead body