A Darwinian puzzle is a trait that appears to reduce the fitness of individuals that possess it. Such traits attract the attention of evolutionary biologists. The phrase "Darwinian puzzle" itself is rare and of unclear origin; it appears most often, but not always, in the context of animal behavior.
A peacock shows an example of a trait that may reduce its fitness. The bigger the tail, the easier it is seen by predators and it also may hinder the movement of the peacock. Darwin, in fact, solved this "puzzle" by explaining the peacock's tail as evidence of sexual selection; a bigger tail confers evolutionary fitness on the male by allowing it to attract more females than other males with shorter tails.
Applications in Nature
Darwinian Puzzles are evident in nature, even though it appears to reduce the fitness of the individual that possesses it. Different individuals use the odd phenomenon in particular ways such as toxins, fitness demonstration, and mimicry.
The following phenomena are sometimes called Darwinian puzzles:
- Altruism in animals
- Homosexuality in animals
- Cellular senescence
- Monarch Butterfly: The Monarch butterfly is a species that has an orange and black wing pattern that is very easy to spot. This coloration of the monarch is non-beneficial to its fitness. It is not beneficial because the bright colors will attract their predators. However, they are able to counteract this non-beneficial trait because they have the ability to feed on poisonous milk weed which deposits potent plant poison in their tissues. Therefore, when a predator ingests them it will induce them to vomit, because of the poison within the butterflies system. Though a monarch butterfly will be sacrificing itself through this process, it is able to help its own kind by educating their predators as to the harmfulness of eating them. The genetically similar monarchs will then be able to survive and pass on the shared genes to the next monarch generation.
- Poisonous Dart Frog: The poison dart frog species (members of the Dendrobatidae genus) are another prominent example of an animal that applies to the concept of the Darwinian Puzzle. The bright, conspicuous coloration of their skin is a tactic used to warn predators that they are highly toxic. The two-inch-long (five centimeters) golden poison dart frog has enough venom to kill ten grown men. Indigenous Emberá people brush the tips of their arrows across the frogs’ skin to make the arrows toxic. This method is a highly effective hunting tool and has earned the frog species its name “poisonous dart frog.” Scientists predict that the frogs assimilate their toxins from the prey that they eat consisting of ants and termites. The frogs demonstrate the Darwinian Puzzle because of the bright coloration that would be thought to attract predators. Instead, they present themselves as a warning.
- Gazelle Stotting: The Darwinian Puzzle also manifests in the behavior of gazelles when they stott. They do this to advertise to predators that they are physically fit and the predator will not catch them if they choose to pursue. This is a form of predator deterrence, but at the same time it makes the gazelle more visible to the predator. There is also more caloric expenditure when the gazelle stotts which would be counter-intuitive to survival. Another Darwinian puzzle that scientists are trying to interpret is the stotting behavior of Thomson gazelles. The gazelle sacrifices its speed whilst escaping from one predator, but searches for other predators up ahead. Another potential reasoning for this stotting behavior is that it will alert their herd that a predator is nearby. Predators, such as cheetahs, realize that when a gazelle is stotting they are less likely to capture their prey so they abandon hunts.
- Conspicuous Spider Web: There are orb-weaving spiders that spin webs with zigzag patterns that are clear, and visible to their prey. The visibility of the web decoration is thought to deter prey from the web, but in actuality it acts as a lure to draw the prey into it. The prey is more inclined to avoid the visible patterns and become caught in the webbing between the zigzag patterns. The spiders also use it as a form of camouflage to obscure their bodies. Studies have shown that orb-weaving spiders with ornamented webs have greater success catching prey than the unornamented web spiders.
- Mimicry: Many species have the trait known as mimicry which allows normally harmless creatures to appear dangerous. Harmless hoverflies are an example of a species that exhibits mimicry. Hoverflies mimic the look and sound of wasps. Though most of them resemble the wasps very closely, others barely pass as looking like the wasps. In order to solve this Darwinian puzzle of why certain hoverflies do not resemble the wasps closely, Canadian researchers conducted a study. In this study the researchers determined that larger hoverflies will closely resemble the wasps where the smaller species barely mimic them. This was determined to be due to the larger species having a greater threat of being attacked by birds. The smaller species do not have to worry about closely impersonating the wasps as much because the birds will not even bother to try and attack them due to their size. Since the larger hoverflies impersonate the wasps, they will have a greater chance of surviving and will therefore increase their fitness.
- Mallet, J. & Singer, M. (2008). Individual Selection, kin selection, and the shifting balance in the evolution of warning colours: the evidence from butterflies, 32 (4). 337-350
- Poison dart frog dendrobatidae. National Geographic, Retrieved from http://animals.nationalgeographic.com/animals/amphibians/poison-frog/
- Alcock, J. (2009). Animal Behavior (9th ed.). Sunderland, MA: Sinauer Associates, Inc.
- Ghosh, P. (2012, March 21). Researchers solve Darwin's copycat evolution puzzle. BBC
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