Alfred Russel Wallace’s take, explicitly.
From ScienceDaily:
Not every encounter between predator and prey results in death. A new study co-authored by a University of Tennessee, Knoxville, professor suggests that prey emit warning cues that can ultimately lead to both their survival and that of their predators.
The hypothesis addresses a 150-year-old mystery of evolution on how warning signals of animals and plants arise and explains animals’ instinctive avoidances of dangerous prey.
…
In 1867, Alfred Russel Wallace, co-proponent with Charles Darwin of the theory of evolution through natural selection, proposed that animals evolve colorful, distinctively recognizable appearances to advertise their distastefulness or toxicity to predators. Despite a number of attempts, however, no satisfactory evolutionary mechanism for the origin of warning cues has been proposed.
Leading theories postulate that predators know to avoid prey after eating one that harmed them.
By “leading theories,” the researcher means Darwinism, of course.
The obvious problem, possibly not evident to the Darwinist, is that the “last meal of the condemned” approach to safety training is not very efficient over the long term.
Burghardt and Weldon suggest predators don’t have to learn to avoid prey from the experience of eating distasteful or poisonous ones. They instinctively know to stay away because they are sensitive to the prey’s chemical signals or they recognize the visual or behavioral warning cues being displayed. They call this mechanism “concurrent reciprocal selection,” which means the signals being emitted by the prey and the predators’ sensitivity to the signals repel one from the other and work simultaneously, ensuring both can survive. A predator that ignores its sensitivity to the toxic prey perishes, as does the prey that is consumed.
This approach might be correct or incorrect in a given case, but it certainly makes more inherent sense. The prey’s warning signals (alarming sights, sounds, smells, etc.) may code for a neurological avoidance response in the predator.
Of course it wouldn’t always work; the predator may be too desperate to care. But it may work just enough of the time that the trait gets passed on by both parties. As for complex signalling, remember, at one time we didn’t know about the bee dance either…
Here’s the abstract:
Casualties and impediments inflicted on consumers by defended prey, and vice versa, may be averted by vocalizations, postures, coloration, scents, and other warning, or so-called aposematic, displays. The existence of aposematic signals has challenged biologists who have sought plausible mechanisms for their evolution. Here, we elaborate on the rationale for the hypothesis that aposematic signals arise via concurrent reciprocal selection (CRS) enacted between inimical signal receivers and signal emitters, where signal emitters, e.g., defended prey, select against non-discriminating signal receivers, e.g., predators, and signal receivers select against unrecognized signal emitters. It is postulated that this mutual selective interaction culminates in the survival of discriminating signal receivers that avoid signal emitters, and recognized (distinctive) signal emitters that are avoided by signal receivers. A CRS hypothesis for the evolution of aposematism, therefore, maintains that distinctive features of prey arise in response to selection imposed by consumers, and that avoidances of those features by consumers arise in response to selection imposed by defended prey. We discuss the plausible inception of aposematism via CRS in light of related hypotheses, and describe points of concordance with previous observations and suggestions on the origin of aposematism. Aposematism arising via CRS is not contingent upon the relatedness of signallers, aversions acquired by learning, or other conditions postulated for some other evolutionary hypotheses. CRS is a credible alternative hypothesis for the evolution of warning signals in diverse consumer-prey interactions. (paywall) – Paul J. Weldon, Gordon M. Burghardt. Evolving détente: the origin of warning signals via concurrent reciprocal selection. Biological Journal of the Linnean Society, 2015; DOI: 10.1111/bij.12565
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