State of the Planet

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The Red Queen and The Evolution of Sex

Photo of Marine Iguana on Isabela Island by Brian Kateman

In the biological world, both within and between species, adaptive progress and success are relative. This notion of evolutionary relativism is known as the Red Queen Effect, a term derived from the Red Queen’s race in Through the Looking-Glass by Lewis Caroll, in which Alice runs with fervor but remains in the same spot.

“Well, in our country,” said Alice, still panting a little, “you’d generally get to somewhere else — if you run very fast for a long time, as we’ve been doing.”

“A slow sort of country!” said the Queen. “Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!”

Matt Ridley popularized the term in his book, The Red Queen: Sex and the Evolution of Human Nature, which contains numerous examples of the constant evolutionary arms race between competing individuals and species.

Consider one of his first examples – a narrative on the relationship between bears and seals. Many years ago, brown bears may have found it particularly easy to catch seals because they hadn’t evolved a fear of enemies on the ice. With fearlessness varying in the population of seals, and under genetic control, those individuals, which were most timid, survived and produced the most offspring, because they avoided predation by the bears. Soon, the seals became more and more careful and successful predation for the bears became increasingly difficult. Try as they might, the contrast of the brown fur with the white snow made it nearly impossible for the bears to sneak up on the seals. Imagine, however, that during a chance mutation, a group of white bear cubs were born. They were incredibly successful because they were afforded the stealth of camouflage, roaming alongside the white snow, able to avoid the seal’s detection altogether. The seals, once successful, had returned to where they had started, no more or less efficient at avoiding predation. Engaging in an evolutionary arms race, both the seals and polar bears developed an adaptation toward avoiding predation and securing prey, respectively. An improvement in one species will inevitably lead to a pressure for the emergence of an equally effective adaptation among the competing species.

Though the Red Queen affects the evolutionary relationship of different species, for example, among predators and prey and parasites and their hosts, they also play a vital role in shaping the behaviors and physiology of individuals in the same species. Take for example the search for mates among male marine iguanas, who scatter several of the islands in the Galápagos. Though male iguanas do not engage in serious combat, they do engage in territorial encounters when striving to acquire mates, congregating in loose associations called leks. During a confrontation, the males sport their flashy colors on the side of their body and swing their head at one another repeatedly until one of the marine iguana retreats – the winner, usually the largest and brightest will have the opportunity to mate. If body size were not constricted by other factors, such as body temperature and foraging efficiency, sexual selection would push for increasing massive marine iguanas. Still, despite an increase in body size over evolutionary time, a female marine iguana is only impressed by the size of a male relative to the other males in the population. Success is once again relative – the Red Queen is at work.

Emphasizing the importance of selection within the species, as opposed to between, Ridley tells the story of a philosopher who is running along side his friend, away from a ravenous bear. His friend warns him that despite his efforts, he will never succeed in outrunning the lighting-fast bear. The wise philosopher replies that he doesn’t need to outrun the bear – he simply needs to outrun his friend.

Ridley furthermore draws upon the Red Queen to explain the advantages of sex, arguing its superiority to two other hypotheses: The Vicar of Bray and the Tangled Bank. The Vicar of Bray asserts that sex serves to respond to environmental changes, and the Tangled Bank argues that diversification of the species, produced by sex, is favored in environments of intense competition and limited resources. Ridley provides a convincing case that sex, through the combination and recombination of genes, is instead a means of preserving genes that are vital in resisting harmful parasites. Diseases are experts in breaking into cells, releasing protein molecules that bind to the proteins on the surface of cells in the host. Evolving in a relatively short amount of time, parasites are continually mutating new proteins they may fit the host’s proteins. Sexual reproduction enables the host species to disrupt this key and lock relationship, evolving new genetic defenses that allow them to live on. In a witty prose, Ridley protests, “I believe that a century hence biologists will look back and declare that the Vicar of Bray fell down a tangled bank was slain by the Red Queen.”

At the end of his book, Ridley introduces evolutionary psychologist Geoffrey Miller, who argues in his book, The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature, that the choosiness of individuals in search of a mate led to an increase in intelligence, comparing the wit, inventiveness, and smarts of humans to the tail of a peacock:

“I suggest that the neocortex is not primarily or exclusively a device for toolmaking, bipedal walking, fire using, warfare, hunting, gather, or avoiding savanna predators. None of these postulated functions alone can explain it explosive development in our lineage and not in other closely related species… The neocortex is largely a courtship device to attract and retain sexual mates: Its specific evolutionary function is to stimulate and entertain other people, and to assess the stimulation attempts of others.”

Through the use of simple examples, an array of thought provoking exercises, and a coherent presentation of the evolutionary history of sex, Ridley challenges the reader to rethink his or her views on the diversity of the planet, even for our own species.

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Dave
12 years ago

Iguana’s got to love them! Remember seeing bunch of them wonder around when I was in Mexico. Interesting article by the way.