Posts Tagged ‘Darwin’

Darwin’s finches – and Darwin’s humans

Tuesday, August 16th, 2011

Darwin gets a lot of credit in biology.  And rightly so, given the sheer quantity of persuasive proofs and fascinating conundrums that he put forth during his career.  This is a man who saw a foot-long nectary on an orchid from Madagascar and asserted the existence, sight unseen, of a moth with a proboscis long enough to reach the nectar at the bottom and pollinate the flower.  Forty years later he was proven correct.  So it is no exaggeration to say that Darwin left a legacy of leads for his intellectual inheritors, many of whom are fond of claiming Darwin not only as an ancestor but also as the source of all of the best ideas and problems in evolutionary biology to this day.

The Galápagos Islands have long been the scene of such claims. Darwin travelled around the world from 1831 to 1836, but he spent barely over than a month exploring the Galápagos.

Map of the Galápagos Islands, from Darwin's Journal of Researches, published in 1839.

Even so, this volcanic archipelago off the coast of Ecuador became one of the iconic locations of Darwin’s Beagle voyage.  Because of the attention that Darwin drew to the evolutionary dynamics of the Galápagos, the islands became a so-called “natural laboratory,” where biologists have gone for generations to watch evolution in action.

In this month’s issue of Evolution, researchers led by Fernando de León from McGill University in Montréal chose these iconic islands —and one of their most iconic groups of animals, the birds known as Darwin’s finches— as the arena for tackling an appropriately Darwinian question: How do humans alter the trajectory of other species’ evolution?

This question is at the heart of Darwinian theory itself.  The very name that Darwin gave to his mechanism for evolutionary change reveals how difficult it is for humans to think about evolutionary change without becoming self-referential.  Natural selection is actually a passive process in which nobody is directly or consciously selecting anything.  The wing length or leaf shape or antennae placement that is “selected” is merely that which allows the animal or plant to face the challenges presented by its environment and have babies that can do the same.  The term “natural selection” reflects the analogy that Darwin made between what happens in nature, the product of mere survival, and what happens when humans interfere with nature and breed specific features into animals and plants through artificial selection.

In other words, humans have long been altering the trajectory of other species’ evolution.  But animal and plant breeding is only the most obvious and most intentional way that we do this.  As animals ourselves, with our own needs and interests, we have also been unintentionally changing the course of evolution since we came into existence.

How do we evaluate the evolutionary effects that we have on other organisms?  More to the point, must we evaluate them?  All animals and plants irrevocably shape the evolution of others in ways both large and small.  How many of these organisms waste time worrying whether these evolutionary impacts are good or bad?  It’s probably safe to say that Homo sapiens are the only ones.

In the case of Darwin’s finches on the Galápagos Islands, our authors begin with the premise that the human effect on evolution is a bad one.  They investigate the loss of diversity within a particular population of finches.  Darwin’s finches are distinctive for their specialized beaks, whether they eat insects or nectar or cacti.  Medium ground finches (Geospiza fortis), the focus of this study, eat seeds.

Four of the fourteen species of finches found on the Galápagos, an image from Darwin's On the the Origin of Species, published in 1859.

Following this particular species over the decades, researchers have observed that it appears to be diverging into two specialized “morphs,” two groups with different beak forms. Medium ground finches with larger beaks specialize on larger, harder seeds, and those with smaller beaks specialize on smaller, softer seeds.

But the population in Academy Bay on Santa Cruz Island looks different.  Academy Bay is one of the more populous human communities in the Galápagos and, as a result, human foods have become more and more available to the finches.  This wealth of new food has slowed down the evolutionary divergence-in-action, leading to the slow homogenization of beak sizes in the Academy Bay population.

As de León and his colleagues put it, human food is “eroding the diet-based disruptive selection that is thought to have previously maintained beak size modality in G. fortis.”  Simply put, elsewhere in the Galápagos, the natural food sources of these birds seem to be driving the evolution of these finches into two distinct groups.  But the presence of humans and their foods stifles this evolutionary process.

Why do we care about “eroding” the “disruptive selection” in the Galápagos—or anywhere, for that matter?  One critical reason is that this type of selection maintains diversity.  And diversity represents evolutionary potential.  In a world that changes all of the time in unpredictable ways, diversity is the source of adaptation to change.  Genetic diversity within populations is a natural resource, an evolutionary reserve; if climate change eliminates the food source that most individuals in a population rely upon, a few hardy survivors could still exploit some new and unanticipated food source.  But that potential only exists when there is diversity within a population.  It’s trite but true: diversity is the raw material of evolutionary adaptation.

The authors conclude that the case of the medium ground finch in Academy Bay is another example of “the importance of conserving the processes that generate and maintain biodiversity, rather than just the product of those processes.”  The products, of course, are the organisms themselves.  This approach to conservation has become increasingly common in recent years.  Its proponents argue that we miss the point of conservation when we champion the cause of individual species and ignore the processes of biological change that generate the all-important, more valuable prize of diversity itself.

As arguments for conservation go, protecting an evolutionary process probably does not tug the heartstrings of most nature lovers.  And as an intellectual argument, it’s important to note that evolution and evolutionary processes do not themselves have any intrinsic value.  When we argue for the conservation of an evolutionary process, we must argue for it as an investment in the future, an investment in the generation of biological unpredictability in all of its incipient evolutionary potential.

But it’s difficult to know precisely how an evolutionary process may be conserved, and it’s a question that the authors do not address in this paper.  In the case of Darwin’s finches, you might assume that the authors would advocate the restoration of the disruptive selection “eroded” by the availability of human foods.   But they could hardly argue for the elimination of the human influences on finches in Academy Bay.  After all, without humans, these biologists would have missed their chance to watch a new evolutionary story playing out.  In other words, while the human community in Academy Bay could be taken as a threat to the Galápagos, we can also appreciate how it increases the archipelago’s utility as a “natural laboratory.”

Even Darwin’s finches could find some utility in their entanglement with humans.  Without access to human foods, the medium ground finches of Academy Bay may have continued to diverge into two new species, each one specialized on its respective food source, thanks to its respective beak size.  The multiplication of species is certainly a form of diversification.  The irony, however, is that specialization does not necessarily lead to great adaptability in the future.  In this sense, then, losing the close linkage between a specific food source and a specific beak morphology could be a boon for the medium ground finch, a generalizing force that might allow them to exploit a variety of foods in the unpredictable future that they face.

Should these last arguments for the utility of human influence make your inner conservationist cringe, consider that humans have always influenced —and been influenced by— the evolutionary trajectories of other species.  It’s only recently that scientists have seen this form of evolutionary interaction as suitable for naturalistic investigation.  And what more appropriate place to investigate the place of humans in evolutionary processes than in the iconically Darwinian Galápagos Islands?

Darwin’s dirty little secret

Thursday, February 12th, 2009

An otherwise inspired tribute to natural history buries the fossils of Darwin’s theological ancestry and misses its chance to challenge Intelligent Design.

10-pound bill

When “Darwin: The Evolution Revolution” first opened at New York’s American Museum of Natural History in 2005, creationist critics were among its first visitors.  Reviews on Intelligent Design blogs found the show “biased” and “dogmatic,” and, even worse, burning with a “Darwinian fundamentalist” zeal.

What gives?  Thousands of visitors have already enjoyed this exhibit in New York, Chicago, Boston, and Toronto.  It’s currently on display at the Natural History Museum in London, as Britain gears up for the 200th anniversary celebration of Darwin’s birthday on the 12th of February.  Will hordes of visitors look back on the exhibit and remember what a hard time those doctrinaire Darwinians gave God?

I doubt it.  In fact, Intelligent Design will be the last thing on visitors’ minds as they reflect back on “Darwin.”  And frankly, I think that’s a shame.  If an exhibit about Darwin’s legacy is not the perfect place for biologists to face the Intelligent Design movement, then where will they do so?

This exhibit promises to unpack the wild and woolly head of one Charles Robert Darwin and, to a large extent, it delivers.  We meet Darwin in his privileged early-19th-century childhood, where he picked up the compulsive habit that would haunt him his entire life: Collecting the flotsam and jetsam of the English countryside when he should have been studying, making him a “scapegrace” according to his physician father.   But Darwin turned his disgrace into a virtue, learning to “look closely” at all of nature, mastering the ultimate “simple tools” of an authentic biologist, his own eyes.

These two themes of the exhibit, “Looking Closely” and “Simple Tools,” are put to elegant use, connecting visitors with the lived experiences of Darwin.  We peer through Darwin’s magnifying glass and stand in a replica of the study where he wrote the great tomes of his adulthood.  The exhibit shares iconic Darwinian stories, like his mad questing for beetles, which drove him once to “collect” a beetle in his mouth, for want of a free hand.  The beetle spewed an acrid repellant, an effective way to avoid being eaten, whether by a hungry bird or a desperate naturalist.  Paired with historical artifacts—in this case, beetles collected by Darwin himself—these stories bring him to life and reveal an intimate contact with nature, cultivated from childhood onward.

When I caught the exhibit last year at the Royal Ontario Museum (ROM) in Toronto, I had a chance to speak with its local curator, entomologist Chris Darling, who shares more than just a passion for insects with Darwin.  As a child, he too spent a lot of time outdoors, laying the experiential foundation for his life as a biologist.  According to Dr. Darling, an urgent concern addressed by the exhibit is “the demise of the naturalist,” the disappearance of biologists who concentrate as intensely as Darwin (who spent nearly a decade becoming the world’s expert on barnacles) while maintaining a broad base of knowledge and experience, observing and cross-referencing information from diverse sources.

And the exhibit certainly samples from many of these diverse sources, bringing home the enormity of Darwin’s accomplishment. That is, the synthesis of such a swarm of biological and textual information that most people would simply give up and go home.  In this exhibit you may catch African spurred tortoises mating, touch a replica of the giant extinct armadillo fossil that Darwin found in South America, and witness moments of startling insight, recorded in Darwin’s own hand, in an original research notebook.

Visitors to the ROM on opening day were dazzled by the dual quality of breadth and depth on display.  “How could you not be impressed by a man who acquired so much scientific knowledge during his life?” commented a young woman, an American tourist who proudly informed me of her Christian faith.  Another visitor, an aging Torontonian schoolteacher, struck by Darwin’s wealthy background, saw the exhibit as a demonstration of what can be accomplished by specialist scientists when they have sufficient resources to delve deeply into a topic. Natural history museums worldwide should applaud this exhibit for the case it makes in support of “Darwinian” science: Visitors see the value of collection and careful observation, and the ever-expanding catalogue of life that is the backbone of modern biology.

By contrast, the molecular tools that many of today’s evolutionary biologists use in their daily work merit no more than a cameo.  For this omission we can hardly blame the creators of the exhibit.  After all, “Darwin” is already packed with artifacts and ideas, and its creation must have been an excruciating surgery, where the organs excised seemed just as vital and vibrant as what remained.  Pride of place is rightly given to the specimens, tools, and documents of a Victorian naturalist.  Yet, despite the success of this central theme, the curators’ scalpels went astray when they carved away the history of Darwin’s theological education. What seemed like a vestigial organ to them—a useless bit left over from our ancient ancestors, like your appendix or coccyx—was more like Darwin’s carotid artery, the wellspring of some of his most important observations.

At the risk of sounding a lot like those complaining creationists, I protest: there wasn’t enough Intelligent Design in the exhibit!  And I’m not talking about bringing in the masterminds behind the Big Valley Creation Science Museum in Alberta to give “Darwin” a facelift.  Instead, I’m talking about the very heart of Darwin’s scientific training at Cambridge, natural theology, which took his love of “looking closely” at organisms and turned it into a scientific skill.

Instead, Darwin’s deepest scientific insights seem to arise de novo.  In its effort to depict Darwin as a revolutionary, the exhibit text implies that he was the first person to critically examine similarities between different species.  In “The World Before Darwin,” we are told that all species were considered “unconnected and unrelated.” The text asks, “Why didn’t more people grasp that similarities in skeletal structures—so clearly visible—were a clue that species are related?”

Why?  Because the best comparative anatomists of the day, Darwin’s own mentors and colleagues, saw the shared skeletal structures of different species, known as homologies, as evidence of God’s design, his master plan for the living world.  Darwin was able to challenge this view only because he had assimilated its lessons so fully.

When the young Darwin looked closely at the world, he saw those homologies just as clearly as his colleagues did, as evidence of design.  But like other good observers of his day, Darwin began to see the flaws in this approach.  If God were so intelligent, why would he give a bat’s wing, a human’s hand, and a whale’s flipper the same skeletal structure?  Didn’t he have the basic engineering chops to devise specialized designs, better suited to the job that each type of limb does?

As Darwin learned more about anatomy, collecting animals both extinct and extant, he came to see homology as evidence for evolution.  And he had no trouble convincing his colleagues, also students of natural theology, of the same. Today, homology still stands as one of the most vivid demonstrations of our evolutionary heritage.  Our human hands share a skeletal structure with a bat’s wings and a whale’s flipper because we all share an ancestor in the distant past.

Because of the visual power of homology, the exhibit relies on it as evidence for evolution more than once, making the absence of natural theology that much more regrettable.  In leaving out this part of Darwin’s story, the creators didn’t ditch a pesky detail only a historian could love.  They missed an opportunity to explain the early prehistory of Intelligent Design, which is basically, “Been there, done that.”

How can we explain this oversight?  It may be, as ROM CEO William Thorsell commented at a media preview, that “Darwin is still too hot to handle.”  After all, “even in Canada,” it was impossible to find corporate sponsorship to support the exhibit until nearly a week after its opening.  In seeing the controversial content on their hands, perhaps the exhibit’s creators decided that Darwin’s training in 19th-century “Intelligent Design” was better left unmentioned.

In portraying his religious sentiments as nearly nonexistent, they sanitized the exhibit of Darwin’s dirty little secret, his theological education. We learn that Darwin, who was trained as a clergyman at Cambridge, brought a swanky engraved German Bible on his five-year voyage around the world, along with his more practical pistol and “peacemaker” club.  Anyone who has studied Darwin’s letters could tell you that he was, in his own words, “a very poor German scholar,” an insight that confirms what is implied by this display case: the Bible was just an accoutrement of travel, perhaps more effective as a weapon than as a source of inspiration.

And how do today’s biologists deal with God?  In answer, a human-sized video screen simulates conversation with a number of prestigious biologists, a valiant attempt to create some kind of dialogue. But the conversation is one-sided. And guess who’s talking?  God-fearing head of the Human Genome Project, Francis Collins (not an evolutionary biologist), blandly assures us that faith and science are “complementary.” A nattily dressed engineering student described the video as “interesting” but hardly enlightening.  “It still leaves a lot of questions for me.  I don’t think I understand anything more about the controversy.”

Nearby, a biology textbook is displayed, branded with the kind of disclaimer sticker disseminated by the Intelligent Design movement, claiming that evolution is “only a theory.”  Another video tries to answer this challenge: scientists stand again in a featureless room, talking at the visitor, explaining that a “theory” in science is not merely a guess, but a critical “framework” within which facts are understood.

But these videos are all just talk.  Visitors have been told time and again, before they even arrived at the “Darwin” exhibit, that science is dynamic, self-correcting, allowing its most treasured principles to be toppled in the face of solid evidence.

Ironically, the story of natural theology, so carefully avoided in this exhibit, is a real-life account of just how such foundational concepts in science may be challenged. Though it is neither biased nor fundamentalist, as creationists claim, in overlooking the “Intelligent Design” in Darwin’s own intellectual history, this exhibit misses an authentic demonstration of the ideals it professes.  Worse, it sidesteps a meaningful discussion of Intelligent Design and why—as science—it just doesn’t cut it.