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For Darwin Day: Cannibalism, like suicide, is adaptive

Common Goby male/Martin Vallon

Remember this? Bees and ants provide clue to human suicides?

Those eusocial behaviors, understood as part of what is called inclusive fitness in evolutionary biology, are adaptive.

“The idea is if you give up yourself, which would include your genes, it can be evolutionarily speaking ‘worth it’ if you spare or save multiple copies of your genes in your relatives,” Joiner said. “It’s a net benefit on the gene level.”

However, when the researchers look at human suicide in a modern context, they surmise that suicide among humans represents a derangement of the self-sacrificial aspect of eusociality. More.

Notice the huge assumption everyone is asked to accept up front, that humans and social insects think similarly. A thesis that bizarre must belong to one or another school of Darwin thought, in this case “inclusive fitness ” or group selection.

Well, just in time for Darwin Day, we hear that eating one’s offspring is adaptive too:

From ScienceDaily:

Once the female of the Common Goby (Pomatoschistus microps) has laid the eggs, only the male looks after them. Sometimes he guards several clutches by different females, cleans the nest, and fans oxygen towards the eggs to improve their supply. Yet scientists have repeatedly observed males eating some of the carefully-provided for eggs. Filial cannibalism often occurs in fish species in which males care for the eggs or young. Earlier studies sought to find out what external factors influenced the timing and the extent of the phenomenon. “Various hypotheses predict that the seemingly paradoxical cannibalism serves to get rid of damaged eggs or that reducing the number of eggs means that the remaining ones are better supplied with oxygen,” says Katja Heubel, “and that the male may do it to compensate for his own lack of food and energy.” She says the results were ambiguous. “Researchers usually assumed that all fish act similarly under the same conditions. In our study, we aimed to challenge that.”

Cannibalism can occur in a variety of animal species, but is usually linked to distressing circumstances. A female cat, for example, may eat a dead kitten, not because she has done some adaptation calculation, but because she needs food and does not recognize the carcase as her kitten any longer.

The Tübingen researchers compared individual male Common Gobies’ behavior while the fish were caring for their eggs and while they were not. “Individuals with a high general level of activity were much more likely to cannibalize the brood,” Katja Heubel reports. The researchers hypothesize that cannibalism is part of a behavioral syndrome — a kind of spill-over response which the male cannot control or fine-tune. “However, a generally active animal may have advantages in other situations, so that this personality trait has been able to maintain itself in the evolution,” Heubel explains.

A simpler explanation is that the male who is less active is in some kind of distress and is simply not behaving normally.

The second study indicates that filial cannibalism in the Common Goby is not completely uncontrolled in all aspects. The younger eggs, which are more frequently eaten, are of less reproductive value than the older, more developed eggs in which the male has already invested more time and effort. And theoretically, every additional day to maturity is a day in which some developmental problem could occur. That means the older eggs have better chances of reaching the stage of independent hatchlings. And — on the other side of the slate — the younger eggs are more nourishing for the adult male. “The males don’t just gobble the eggs up at random,” says Heubel. It appears that this filial cannibalism — on the face of it, destructive and counterproductive — is a part of an adaptive behavior. More.

The male fish of course, has been keeping records and knows this. Or else the Selfish Gene has been keeping records and knows this.

Actually, the fish probably eats whatever he thinks is food, whether that behaviour is adaptive or not. If something has been around for a while and he hasn’t eaten it, he may be less likely to decide it is food. The behaviour may be adaptive or, practised systematically, it may result in a decline in the numbers of the species.  We don’t know about the behaviour of extinct animals, so we don’t have the comparison that would be most helpful her.

Can a reader come up with a single behaviour that is not “adaptive,” when Darwinism stands in for science?  No wonder there are growing cries for reform. A thesis that demonstrates everything demonstrates nothing.

The thing about Darwinian thinking today is that it doesn’t need to be grounded in anything other than Darwinian thinking.

One wonders what Evolution Sunday will drag in.

See also: Could we all get together and evolve as a group?

For a bit of background on really different brains and behaviour: Does intelligence depend on a specific type of brain?

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Here’s the abstract:

(paywall) Although counterintuitive at first sight, filial cannibalism is common in the animal kingdom and has been recognized as a mechanism to increase the cannibalizing parent’s lifetime reproductive success. However, previous evidence is often inconclusive and the adaptiveness of filial cannibalism is still not fully understood. We here address the notion that parents do not cannibalize at random but preferably consume offspring with a particular phenotype. To assess if differences in developmental stage and thus reproductive value of eggs trigger such selectivity, we experimentally presented male common gobies (Pomatoschistus microps) with two differently aged egg clutches within mixed broods. We found that males consumed significantly more young than old eggs. This result indicates that parents are not only able to discriminate between eggs based on developmental stage, but might use this to reduce the cost of partial filial cannibalism by selectively removing eggs of lower reproductive value. – Martin Vallon, Katja U. Heubel. Old but gold: males preferentially cannibalize young eggs. Behavioral Ecology and Sociobiology, 2016; DOI: 10.1007/s00265-016-2074-6


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