This year marks the 200th birthday of one of modern history’s most influential thinkers, Charles Robert Darwin. It is also the 150th anniversary of the publication of his most influential work, The Origin of Species.
Charles Darwin was born in England in 1809 to a wealthy family who expected him to enter the clergy. Instead, Darwin managed to gain passage aboard the HMS Beagle and the rest, as they say, is history. His trip aboard the Beagle brought him to South America, the South Pacific, and most famously, the Galápagos Islands. This voyage not only gave him the inspiration to write the popular travel book The Voyage of the Beagle but also provided the fodder for a revolutionary theory.
Darwin postulated that evolution, speciation, and the explanation for the wide variety of living organisms could be driven by a force known as natural selection. His theory explains how the coupling of environmental and sexual pressures can select for variation both within and between species.
Notably absent from Darwin’s theory is the mention of a divine creator. Darwin was acutely aware of how inflammatory his theory of natural selection was, especially in a Victorian setting, and therefore kept it under wraps, only discussing it with a few supportive naturalists.
It was only when he received an essay from Alfred Russel Wallace describing a similar theory that Darwin was pushed to submit a co-written paper on their theories. Because he waited an astonishing 20 years to publish his findings, Darwin was able to amass a large amount of data to support his claim.
Dr. Aneil Agrawal, an associate professor in the Department of Ecology and Evolutionary Biology and Canada research chair in the genetics of evolutionary interactions, emphasizes that it wasn’t “just that [Darwin] had the idea, he collected a lot of data.” Through his work, Darwin formulated questions about evolution that researchers today are still trying to solve.
Darwin dedicated his life to understanding the forces that shape species and their behaviours. “It’s remarkable how much Darwin got right, and how much he was able to explain,” says Agrawal. Although Darwin had no knowledge of genes and the manner by which traits are genetically inherited, he did have an understanding of how new variants might present themselves as adaptive characteristics. Agrawal highlights that in an evolutionary biology seminar, it is not uncommon to hear speakers acknowledge that Darwin also considered the problem they are about to present. Darwin often had the correct answer. “It’s only now [that people have] the data, that it turns out that Darwin was right,” says Agrawal.
Darwin had a knack for seeing what we today take for granted. “[Evolution is] clear only once someone has pointed it out to you,” says Agrawal. “In some ways, evolution by natural selection is fairly simple. We can explain [the theory of natural selection] pretty well to first year undergrads. We don’t, for example, teach [Einstein’s] theory of relativity to first year undergrads. It’s easier to grasp the idea of what [evolution] is and how it works.”
The theory of natural selection is accessible, at least at some level, to anyone who has observed the natural world. This may explain the fascination popular culture has with “survival of the fittest,” a phrase that makes most evolutionary biologists cringe. “People are broadly familiar with the idea of evolution and natural selection. Even if they might not understand what it is, they’ve at least heard of it,” says Agrawal.
Today it’s easy to look back at Darwin’s theories and think, “that was obvious, I could have thought of that.” But as Agrawal points out, many bright thinkers before and after Darwin have considered the origins of Earth’s diverse species, yet none have contributed an idea as grand as his to the field of evolutionary biology. Every scientific discipline has its great hypotheses, and Darwin’s theory of natural selection is as big as they get. “There aren’t many of those ideas,” says Agrawal. “Ones that are powerful, yet not that complicated.”
The theory of natural selection set the groundwork for an entire field—evolutionary biology—which has had biologists thinking about selection and the pressures on living things ever since.
Sitting in his bright office that overlooks a tree-filled courtyard of the Earth Sciences building, Agrawal describes how, not unlike the father of his field, he took an interest in animals from a very early age. “I was one of the rare people who always knew from a young age that I wanted to be a biologist.” Being a biologist only got better once he recognized that math could be a part of it. “When I was a little kid I would have never imagined that I would be interested in applying math to biology. But when I was older, [math was] what really attracted me to evolutionary biology.”
Dr. Agrawal has already received a number of awards for his work, including the 2007 Robert H. Haynes Young Scientist Award and the 2004 Theodosius Dobzhansky Prize, both for promise as an evolutionary biologist. He now leads an evolutionary biology lab at U of T. Dr. Agrawal and his team are interested in a number of evolutionary biology problems, including the evolution of sexual reproduction, a concept Darwin also tried to understand.
The overwhelming majority of organisms on Earth reproduce through sex, which demonstrates that it has advantages over asexual reproduction. However, sexual reproduction incurs a number of costs to the individual, including sexually transmitted diseases, the large expense of searching for a mate, and increased risk of predation while mating. What, then, is the advantage of sexual reproduction? This is a question to which Dr. Agrawal devotes a lot of his time. “If I knew the answer to [why sex occurs], I think that I could go home,” he jokes.
Current theories ascribe the evolution of sexual reproduction to its ability to manage the effect of parasites, DNA damage, and the appearance of deleterious mutations. “We’re getting a lot better at eliminating ideas… and a lot better at identifying what are the key issues and the best ways to approach this .” Dr. Agrawal notes that there are a multitude of theories to explain sexual reproduction, and that the correct one is likely nestled among them. “The idea is probably out there, but a bit more complicated than however it has been originally proposed.”
Much of the research in Dr. Agrawal’s lab is carried out on the fruit fly Drosophila melanogaster, which they believe explains a lot about the effect of deleterious mutations on evolution. This was an aspect Darwin didn’t really think about. Dr. Agrawal hypothesizes that Darwin probably would have thought deleterious traits would arise but would be eliminated by natural selection, making them unimportant.
Although deleterious mutations are eliminated from the population by natural selection, they are also constantly being introduced. “They can actually, under fairly reasonable conditions, have dramatic effects on populations,” says Agrawal.
Using fruit flies as a model, the Agrawal lab looks at how genes interact and what effect the environment can have on genetic interactions. Flies make wonderful models for this, as their genes are easily manipulated. As well, there is a wealth of information available on easily observable genetic defects that affect traits such as wing shape, eye colour, and the bristles on a fly’s back. This permits the direct observation of environmental effects on visible traits.
Even within a species, different positions, or loci, of the genome are subject to varying selective pressure. Regions that encode spermatogenesis—the development of sperm in the male testes—and proteins important for the immune system appear to evolve faster than the rest of genome. This makes sense in light of the extreme evolutionary pressure on traits involved in sexual selection. For genes involved in the immune system this can be explained by the pressure to avoid the cost of parasites.
Dr. Agrawal admits that many questions in evolutionary biology still loom large over the scientific horizon. Chief among them are the questions “Why sex?” and “To what extent do the four evolutionary forces—genetic drift, migration, mutation, and natural selection—shape the genome?” He also wonders about the factors that lead to speciation.
Where will these answers come from? Dr. Agrawal believes they will take a concerted effort from field workers, experimentalists, and theoreticians to solve. “I could be hit with my greatest idea ever and figure out what could be the right idea for the evolution of sex. But, you’d still need to do some pretty nice experiments and ultimately field work to provide the data to show it’s true.” He adds that the “revolution in genomic[s] … and the bioinformatics tools for interpreting those data are making big inroads into [these] questions and are sure to continue to do so.”
Darwin would be proud of the progress.
