I remember reading that some species of armadillo give birth to identical quadruplets. Is this true? If it is, is there some kind of adaptive benefit to it and, if so, what is it?


Hi Tim,

it is true that the nine-banded armadillo (Dasypus novemcinctus) always give birth to four identical offspring. This is because the armadillo only produces a single egg, which seperates into four seperate parts after fertilization. This produces four identical, same sex offspring.

The adaptive benefit may be that since all of the quadruplets are the same sex there is no danger of inbreeding between the litter mates (armadillos don't really have a territory, so the young just wander away as they mature, rather than being driven off as they become adult, so inbreeding may become a problem if they were mixed sex). Other than that I can't think of many other advantages. Anyone else got any ideas?

Possibly if the environment is stable, genetic similarity can be advantageous.  If you're well adapted to an environment that isn't changing, it's safer to be conservative with genetic mutation.

Knowing precisely nothing about armadillos, I wouldn't even hazard a guess as to whether this is or was the case with them.

But it's a possible advantage.

It could just be a case of them having going down this unusual evolutionary pathway by chance and getting stuck there. Not all mutations that come about are beneficial, neutral mutations will not be selected against and will remain. In this case it may hve been advantageous in the past, and now they have adopted it, can't change back.

Ah yes, but neutral mutations are not selected *for* either, so it seems odd to have such a trait occurring throughout the population if it is not actively selected for. Even if the strategy is no longer under strong selection, it must have been an advantage in the past, or there must have been a substantial genetic bottleneck for a whole species to maintain such a bizarre and (one would have thought) easily altered reproductive strategy.

Well it could have evolved millions of years ago (it is shared in all armadillos) and if it is dominant then it will have time to spread even if it is neutral.

Even if it evolved millions of years ago there must have been selection pressures that favoured this mode of reproduction. I am sure that it is not controlled by a single gene, and it is not seen in other mammals, so dominance alone doesn't provide enough of an explanation.