Adoption

Beagle and sleeping black and white kitty-01
I had to laugh recently when someone told me that this couldn’t be a sign of intelligence because ‘how smart was it to look after someone else’s kids’. I would have thought this was too obvious to warrant explanation, but apparently not, so here goes…

Evolution remorselessly drives us to multiply our own genes at the expense of all others. Every time our ancestral line has has spawned mutant new genes or new variants of old ones, natural selection seeks out the most selfish. Genes that effect the simplest and most direct behaviours would demand self-centred and nepotistic types were present in spades. Those genes that facilitate extremely complicated behaviour that might allow an individual to ‘think outside the box’ to save their own life have difficulty delivering selfishness with such completeness…

Most animals that adopt young, such as dogs, tend to have ancestors that lived in groups with with very close genetic ties to each other. Members of their typical ancestral group, were far more closely related to each other than surrounding members of their species. You could put it like this: many of their ancestors have been in inbreed groups. This route to significant levels of adoption is almost a rule, yet sperm whales smash that rule. The only other species that I know to come close are humans.

The tightest and most permanent group in sperm whales is the ‘unit’ which consists of about ten individuals. Like wolves, the whole unit helps raise a new born calf. In other words, each pod is a definitive family unit. Genetic testing shows, sure enough, 70-90% tend to be from one matrilineal line. The show stopper is that the other 10-30% are not slightly more distant cousins, but completely unrelated. It seems they have been adopted into the group, with their closest mitochondrial match sometimes being in another ocean! I will speculate here and now that a 10-30% adoption rate of the completely unrelated will prove an order of magnitude higher than for any other animal, and that humans will measure as a distant second by a similar margin over the third highest animal.

No behavioural differences have ever been recorded between the way individuals within one unit relate to adopted verses related members of it. To put it another way, in a multi-unit pod, two genetically related whales from different units will associate more closely with genetically unrelated members of their own unit than each other. If you try to explain this behaviour in term of selfish genes, you would need to invoke social rules so complex that they can convey advantage despite this huge burden. If I had to guess (modelling it properly is an expert task I will gladly leave to others), I would say that from this alone, that the complexity of sperm whale social interactions must be higher than that of humans. I put this out as an open question in need of explanation. I should also add a caveat.

This behaviour could be atypical in sperm whales, and only induced recently through the disruption of whaling. If that were so the mystery, while still significant, would not quite have the depth depicted here. However, their populations are marked by such an extremely high rate of genetic mixing across the entire globe it almost demands this has been the norm from even before the time of commercial whaling.

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