Type: Synthesis Essays
Sample donated: Connie Graves
Last updated: April 26, 2019
In 1848 Henry Walter Bates, an entomologist (and die-hard beetle collector), conductedfield work in the Amazon, where he collated large collections of animals. Bates was afriend and colleague of Wallace and continued to correspond with him during this time,encouraging the development of his theory of evolution by natural selection. After four-teen years in the Amazon, Bates published a famous paper detailing his observations ofcolour patterns in butterflies. He observed that non-poisonous butterflies tend to mimicthe bright warning colourations of poisonous butterflies. Bates reasoned that the non-poisonous butterflies must have evolved, by natural selection, to resemble the poisonousones (see chapter 6). Bates (1863) hinted at the board applicability of theories of warningdisplays and mimicry.
Bates’ work was the first landmark in coevolutionary theory: mimicry was an appar-ently intuitive example of reciprocal evolutionary change in interacting species. However,although evolution was studied rigorously after Darwin’s theory was published, it tooklonger for coevolution and interspecific interactions to receive the same broad attention. Eleven years after Bates’ discovery, Fritz Mu ?ller contributed an extension to mimicrytheory. Influenced by his field work, Mu ?ller (1879) made an argument to show how twopoisonous animals might benefit from sharing a warning colouration.
Whereas Bates re-ported a parasitic type of mimicry (where one species benefits at the expense of at leastone another), the type of mimicry reported by Mu ?ller appeared to be mutualistic. Thus,mimicry offered two forms of coevolutionary interactions: antagonism and mutualism Despite the importance of coevolution to the fundamental questions in biology, it waspushed to the wayside in the early 20th century for a long period of time. Thus, studentsof evolutionary biology were taught only half the problem of evolutionary adaptation.
When interspecific interactions and coevolution was taught, it was done regarding onlyspecific cases, rather than as a general principle (Thompson, 1994). Thus, coevolutionwas pushed back as a focus for evolutionary theorists. What caused this slump in studiesof interspecific interactions in evolution? First, evolutionary biology seemed to lack theappropriate tools for modelling such interactions (although Mu ?ller had shown that simplemathematical approaches could help). Second, and probably most influentially, there werebigger fish to fry.
Although coevolution is a fundamentally important principle, there were even morepressing and immediate problems for evolutionary theory. Two biological paradigms—the naturalist/biometry (statistical study of biology) camp and the geneticist (study ofhereditary and transmission of genes) camp—were apparently at odds (for more detailsee Mayr & Provine, 1980). The stances taken by the two camps seemed incommensu-rable. Many of the problems were down to communication problems and idiosyncraticterminology. However, the problem plagued evolutionary biology. Further, questionssuch as “If parents’ traits are combined in an offspring, then why have the colours of or-ganisms not evolved into a grey blended mess like randomly mixed paint?” were givenas a problem for evolutionary theory. Questions such as this were used as sticks to beatevolutionists. The pathway was left open for a genetical theory of natural selection.
This unifiedtheory was provided by one of the most influential evolutionary theorists: Ronald AylmerFisher. In his highly influential book The Genetical Theory of Natural Selection Fisherunified Darwinism and Mendelian genetics, reconciling biometry and genetics by show-ing that genetics was actually reinforcing biometrics The integration of Mendelian genetics into evolutionary theory also answered thequestion of why everything does not evolve into a grey mess: parents’ traits are notblended but are inherited in sections of genes from each parent’s chromosome. ThusDarwin’s hypothesis that innate characteristics of an organism were somehow passed onto its offspring had finally been paired with a plausible mechanism. Although work on coevolution in general made little progress in the first half of thetwentieth century, mimicry was a notable exception. It carried the flag for coevolutionwith Fisher (1930) devoting an entire chapter to it.
The chapter was the only one to dealwith interspecific interactions in detail. After the shock-waves of the evolutionary synthesis had settled, coevolution made itsway back into the limelight. Not only were the fundamental pre-synthesis questions outof the way, but new techniques had emerged which were well suited to studies of simplecoevolutionary interactions. Game theory is a mathematical technique that was initially developed for use in eco-nomics.
In particular, the use of game theory to find Nash equilibria1 was proving usefulto evolutionary thinkers. Due to the parallels between economic change and evolution, itbecame apparent that game theory could be applied to theoretical studies of coevolution-ary phenomena. This application was championed by the highly influential and respectedbiologist John Maynard Smith (see e.g., Maynard Smith, 1982). The availability of gametheory as a tool (and later, fast computers and other techniques) led to an increase in workon these topics.
An important example of the success of the game-theoretic approach was in workon the evolution of communication. In an often-cited paper, Krebs and Dawkins (1984)described interactions between species in terms of mind-reading and manipulation. (Theperspective introduced by Krebs and Dawkins will prove useful later on in this thesiswhen we develop a theoretical understanding of warning signals and mimicry.) Krebs andDawkins maintain that when there is a conflict of interest, receivers (the animals receivingthe signal) are under selection pressure to critically assess the behaviour of the other inorder to exploit any telltale signs of their intentions, thus extracting useful information.On the other hand signallers are under selection pressure to manipulate the receiver intodoing what they want. Biologist Leigh Van Valen proposed what is now known as the Red Queen principle. Thename comes from the analogy to the Red Queen chess piece in Lewis Carroll’s Throughthe Looking Glass, who explained to Alice “. .
. here, you see, it takes all the running youcan do, to keep in the same place.” Essentially, the principle explains that for an evolvingorganism, continuing development is needed simply in order to maintain its fitness relativeto the species with which it is coevolving (Van Valen, 1973). The only way predators cancompensate for a better defence by the prey (e.g., gazelles running faster) is by developinga better offence (e.g.
, leopards running faster). In turn, prey need to evolve a better defenceto escape predators, which will again be met by an improvement in predator offence; andso the cycle continues. Of course, there is often an escalation limit; the cycle has to stopsomewhere due to physiological, genetical or environmental constraints. Thus, we do notsee animals running quickly enough to break the sound barrier. The red queen effect is not ubiquitous in coevolution.
As Krebs and Dawkins noted inthe case of conspiratorial whispers, some coevolutionary interactions are mutualistic, inwhich the species involved benefit from complementary interactions. Darwin tackled mu-tualistic coevolution explicitly in discussing his ideas on how bees and flowers interact.Darwin dedicated his follow-up to the Origin to this issue and backed up his ideas withsome observations (Darwin, 1877). He imagined the size, length and body form of hon-eybees evolving to better match the shape and length of the corolla tubes surrounding thepollen so as to more efficiently exploit the resource.
Further, he imagined the shape andlength of the corolla tubes to be modified to best allow bees to pollinate them