Why do female penguins attempt to steal young?

October 24, 2005 5:54 PM

Selfish penguin theory: I just saw March of the Penguins and observed the chick-stealing behavior. How is this at all adaptive?

I know that offspring theft occurs in other species, but it seems that selfish gene theory would predict that this behavior become extinguished fast. The "mother" will spend a great deal of resources raising a chick that has none of her genes, at risk to her life and ability to reproduce next season. Yet the behavior (in Emperor penguins, anyway) is common enough that other females recognize and attempt to prevent the theft. How is this explained in terms of evolutionary biology?

posted by nev to Science & Nature (13 answers total)

Hm. I havn't seen the movie, and am not a penguinologist. But perhaps it increases her likelyhood of reproduction the next year, as all the other penguins know what a "dedicated" mother she is.

On the other hand - perhaps it isn't adaptive in itself, but is a subordinate part of a larger, more obviously adaptive behavior. For instance: perhaps it is adaptive to have a very strong default for raising any child you see around you - so that you NEVER, EVER forget your own baby. This would be reasonable.

Also, altruism can frequently be described as adaptive. Perhaps this is a carry-over from a (more) altruistic behavior, such as rescuing any chick that seems to be in distress.
posted by metaculpa at 6:20 PM on October 24, 2005

As a sideline, it's useful to remember that the adaptive hypothesis is just a hypothesis - it assumes that evolution usually creates the perfect solution to every problem, and that any behavior you can identify must increase the fitness (in terms of children or grandchildren born) of the animal doing the behavior. But it's not obvious that this is always the case: the environment may have changed to make a previously adaptive response to a stimulus much more detrimental.

Or, evolution may be trying to balance two competing interests, such that only one behavior is truly adaptive - but having the other behavior around is more important. If there's no way to do both with the current set of genes, then there's a minimax problem.
posted by metaculpa at 6:31 PM on October 24, 2005

I think it's important to read this before looking for looking for an explanation for every "adaptation".
posted by Jimbob at 6:58 PM on October 24, 2005

following metaculpa's train: unless there were less-adaptive traits, as well as adaptive ones, there coudn't be any evolution. But mc's earlier point that the stealing is probably a part of "babies are very desirable" seems the most likely explanation to me too.
posted by anadem at 6:59 PM on October 24, 2005

Also, it depends on how many genes the members of the penguin colony share. The selfish gene theory predicts that if a gene causes a more-dedicated female penguin to steal and raise a baby penguin who also had the same gene, and the result was a higher survival chance for the baby, then the gene will be passed on to future generations more frequently. The gene(s) that cause penguins to steal babies don't "care" whether they deny the thieving mother's other genes the ability to reproduce.
posted by rhiannon at 7:32 PM on October 24, 2005

What Jimbob said. Also to expand on what metaculpa said, "stealing chicks" is a human interpretation of what the behavior is about. It's possible that the underlying behavior is just, "keep a chick/egg in the nest and nourish it at all costs." This also would explain behavior like brooding egg-shaped rocks, and taking care of cuckoos.

Don't assume that every behavior observed in diverse population must be adaptive at first look.
posted by KirkJobSluder at 7:33 PM on October 24, 2005

rhiannon: There is actually some problems with that interpretation of altruism. The basic problem is that the benefits of altruism (in terms of selfish genes and quantitative genetics) drop off dramatically when you go beyond siblings. The end result is that with the exception of homogenous populations such as social insects or isolated kin groups, it's a loosing gamble betting on the possibility that the recipient of your charity will carry enough shared genes to make it worthwhile (in terms of selfish genes and quantitative genetics).

On the other hand, social behavior is frequently a good strategy to increase your own individual reproductive success.
posted by KirkJobSluder at 7:44 PM on October 24, 2005

KirkJobSluder, that's a good point. I think a solution might rest between a balance between altruism, the drive to rear at all costs, and the "well, I'm here anyway, so I might as well" effect - one has to look at the cost at the point of decision making, not just the cost of standing in the wasteland for months.

Or, perhaps, because God Told Them To be monogamous, refuse to speciate, steal babies, and generally be good little penguins.
posted by metaculpa at 8:16 PM on October 24, 2005

I had the same question after the movie. Discussed it with some others and came up with the idea that a female is going to be in a better position vis-a-vis the group (and therefore survival) as a mother than as a solitary female. Of course, IANAP and would love to hear from one.
posted by magwich at 8:26 PM on October 24, 2005

Response by poster: I'm not saying the behavior must be adaptive simply because it exists. My interest arose because from all appearances, it's maladaptive. Other penguins recognize the behavior as abberant and have a violent response to it, which implies that natural selection alone didn't eliminate it. I'm wondering what could possibly have allowed it to persist long enough for the "social outrage" behavior to emerge.

I can believe that it's just a side effect of protecting one's chick at all costs, though.
posted by nev at 8:33 PM on October 24, 2005

Best answer: It's simply a "side effect." Mothering instincts have evolved to be quite strong, so strong in fact they sometimes lead to "baby stealing." Such strong mothering instincts are selected for as they lead to more genetic offspring than weak mothering instincts.
posted by pwb503 at 10:20 PM on October 24, 2005

And with the kind of grueling ordeal they go through to get food (if it's any like the one I saw on an episode of Massive), that mothering instinct has to be, well, simply massive.

I don't know what kind of penguins I was watching in that show, but it occurs to me that perhaps their breeding ground was, long long ago, not a 100km trek over ice to get to ocean. Back in the warm old days, it was probably a pretty decent place to lay eggs.
posted by five fresh fish at 11:22 PM on October 24, 2005

Response by poster: fff: For the Emperor penguins depicted in the film, it's a massive trek only in the fall. By the time the hatchlings are ready to leave the colony in the spring, the ice has retreated to within a few hundred yards. Neat trick.
posted by nev at 10:11 AM on October 25, 2005