Archive for the ‘evolutionary biology’ Category

Making the scientist, making the place for science

Wednesday, March 28th, 2012

Sir Joseph Dalton Hooker


Kew’s exhibition, “Joseph Dalton Hooker: Botanical Trailblazer,” highlights handsome illustrations and provides a personal and professional cross-section of the making of a Victorian scientific career. But tantalizing morsels hint at tensions between public needs and professional goals in the life of a scientist and in the operations of a scientific institution like Kew, leaving the visitor wanting more.

“Kew is what my father and I have made it by our sole unaided efforts,” claimed Joseph Dalton Hooker in the early 1870s, affronted by a Board of Works proposal to eviscerate the scientific function of Kew Gardens.  The proposal to transfer Kew’s herbarium collections of dried plants to a new museum soon to be opened in South Kensington (now known as the Natural History Museum) was politically framed as an attempt to streamline government-funded institutions and reduce spending. But Hooker saw it instead as a direct attack on his scientific career.

He had strived for decades to support himself through botanical work, making expeditions to the ends of the earth to collect new species of plants for Kew Gardens. Finally, in 1855, his father, Sir William Jackson Hooker, the first director of Kew, was able to hire him as assistant director.  And in 1865, with his father’s death, J.D. Hooker became director himself.  But now, just when he had ascended to the rank that would allow him to shape botany into a properly scientific pursuit, this proposal threatened to turn Kew into a mere pleasure garden, and to turn Hooker himself into a mere public servant.

Of course, ever since Kew was made public in 1841, its director was expected to act, to some extent, as a public servant, assisting horticulturalist and farmers at home and abroad with various botanical conundrums.  Hooker himself became known for his aid in transplanting useful plants to colonial outposts: bringing quinine and rubber from South America to India, and disease-resistant coffee from West Africa to Sri Lanka.  But Hooker believed just as strongly that Kew must serve the needs of botanical science, and to that end the herbarium was essential.

Fortunately, the safety of Kew’s herbarium was secured by 1874, thanks especially to the exertions of that infamous firebrand evolutionist Thomas H. Huxley.  But questions about the Gardens’ function remained.  In fact, while this exhibit largely glosses over the near-catastrophe of the early 1870s, comical illustration from later in the decade arrest the visitor’s attention, depicting Kew Gardens as a place where the enjoyment of the public and the work of scientists directly conflicted.  In 1883, the Gardens began opening at noon; but prior to this shift, an opening time of 1pm prolonged the morning hours that scientists and students could work in Kew, undisturbed by the baser concerns of the general public.  This one extra hour of public access was the hard-won product of at least seven years of public protest, if we are to judge by the date on a large cartoon: Inside the Gardens’ walls the privileged few luxuriate while the rabble pickets outside with signs like “Down with the select arrangement. No peace until satisfied” and “Give the public justice.”  This cartoon, as with other such images in the exhibit, is inexplicably unreferenced, which is a shame, since visitors could better understand the illustrations’ significance with knowledge of their sources.

But Hooker’s place as the gatekeeper of Kew’s scientific reputation was also hard-won and it’s easy to understand his staunch defense of the Gardens as, first and foremost, a place for science.  Both his and his father’s early careers had not been easy, and in building the scientific reputation of Kew, he built himself into a scientist in parallel.  His trips around the world had fed the growing herbarium; according to the exhibit, over his 70-year career, Hooker identified more than 12,000 new plant species. Hooker sketched many of his collections while he was in the field.  It’s wonderful to see the handwritten evidence of fieldwork found in researchers’ field notebooks, and Hooker’s sketches of plants and landscapes are some of the most engaging illustrations in the exhibit, drawing the visitor in to Hooker’s travels.

Using these collections, Hooker also asked larger questions about plants. In 1839, when he was only 22, he set off on his first long voyage, working as the assistant surgeon on an Antarctic expedition (though he preferred, according to the exhibit, his unofficial title of ‘Botanist to the Expedition’).  Observing patterns of similarity and difference between plants found on the continents he visited gave him a lifelong fascination with the geographical distribution of plant species.

In highlighting Hooker’s astute observations of the geographical distribution of plants, the exhibit also presents a rather funny incongruity.  Hooker is credited in one breath with cultivating non-native plants like quinine and coffee in the colonial landscape, and in the next with a prescient understanding of the ecological dangers of non-native species.  In particular, we are told that upon visiting various islands in his travels around the Antarctic, Hooker became aware that non-native species were damaging to their “unique plant communities. These problems continue today with invasive non-native plant species overwhelming natural habitats, pushing some native species to the brink of extinction.”  The irony of this is only heightened by Hooker’s renown for bringing the seeds of unfamiliar varieties of rhododendron back from the Himalayas.  As popular plants in the Gardens, some of these may still be seen today in Kew’s Rhododendron Dell—as well as outside the garden where some “escapees” have come to act “invasively,” and are considered a non-native nuisance.

This apparent contradiction is no mistake—in fact, it reflects a cognitive dissonance that still thrives in biology, where organisms may sometimes be cast as emigrants and other times as invaders, where one moment one is a great success in a new ecological niche and the next a weedy marauder.  The identity that a newly introduced species assumes rests to a large extent on cultural context rather than biological fact—which supports no opinion either way.

To be fair, though, J.D. Hooker’s scientific legacy is felt more in evolutionary biology than in invasion ecology.  Hooker began his 40-year friendship with Charles Darwin just as he was setting off on his Antarctic expedition in 1839.  And by the time Hooker left for the Himalayas in 1847, Darwin had confided in him his developing theory of natural selection.  Thus, on this adventure, Hooker travelled, as a video in the exhibit says, with “a shopping list for Charles Darwin,” acting as Darwin’s eyes and ears in the field. “I congratulate myself in a most unfair advantage of you,” Darwin wrote to Hooker, “viz in having extracted more fact and views from you than any other person.” Considering what it must have meant for Hooker to have the seed of Darwin’s theory already planted in his mind a dozen years before the publication of On the Origin of Species, for him to see the vegetation of the Himalayas through that lens, it’s easy to understand how Hooker’s assistance and—later—his support of natural selection became indispensable to Darwin.

This plaque on the wall of St. Anne's church on Kew Green commemorates J.D. Hooker, who was buried in the churchyard outside.

This is the gravestone for J.D. Hooker and his family--considering that he could have been buried near Darwin in Westminster Abbey, this is pretty understated!

“Joseph Dalton Hooker: Botanical Trailblazer” does a good job of touching on many of the major themes in Hooker’s life and work and it is a worth a visit.  But you must hurry to the Shirley Sherwood Gallery of Botanical Art, for the exhibit closes on Monday 9th April. If you wait till after 31st March, you will also be lucky enough to catch Rachel Pedder-Smith’s awesome herbarium specimen paintings.



For Further Information:

The exhibit has a very nice little companion volume, which can be purchased at the Kew gift shop, and features a great introduction by historian of science Jim Endersby.  I admit that I have not read his book Imperial nature: Joseph Hooker and the practices of Victorian science, but it looks like within its pages you can find out more about the near-demise of the Kew Herbarium in the early 1870s, a controversy that was named the “Ayrton Affair” after the head of the Board of Works, Acton Smee Ayrton. (The Ayrton Affair was also just one element within the Royal Commission on Scientific Instruction, also known as the Devonshire Commission.)

For more on the history of the Royal Botanic Gardens, Kew, check out their cool historical timeline.

If you would like to learn more about why I put “invasive species” in scare quotes, read out my own article on the subject at The Naked Scientists and check out this 2011 Nature article, entitled “Don’t judge species on their origins,” which you can actually read for free here, thanks to the US Forest Service!

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?

What’s sexier than sex and warfare? Taking the “arms race” one turn too far.

Wednesday, March 25th, 2009

Talk about sexy science. How could any science be any sexier than sexual selection?

Then combine sexual selection with “nature’s arms race,” and what do you get?  Science so titillating that even a seasoned science journalist might get a little…carried away.

This was the only explanation I could contrive yesterday morning after I read Nicholas Wade’s latest contribution to the New York Times Tuesday Science section. Only last week I posted about the importance of the arms race analogy to my dissertation research on the history of coevolutionary research. So I was very excited to see Wade’s piece, “Extravagant Results of Nature’s Arms Race,” gracing the cover of the Science Times.

Sexual selection is not really my bag—the evolutionary “arms races” that I write about are between hungry herbivores and unpalatable plants, not males of the same species. But the general concept is the same: offense and defense is heightened over many generations as a result of natural selection for the best-fed herbivore, or the least palatable plant, or, in the case of the sexual selection, the most successful (read: sexiest) male.

Sexual selection is a special case of natural selection where the most successful features do not always seem obviously adaptive. Take the classic example, the peacock’s plumage. Its lavishness makes no sense when you imagine the peacock trying to outrun a tiger. What can be more evolutionarily important than avoiding being eaten? Being sexy, of course. At some point in evolutionary history, females developed a preference for gaudy tails, and since the males with the gaudiest tails were the ones getting the action, more pretty boys in the next generation had gaudy tails. And so on– you get the picture.

This “female choice” type of sexual selection does involve an “arms race” of sorts: Peahens’ preference for gaudy tails escalates even as the gaudiness of male tails escalates—female preference and male success mutually reinforce and drive each other to greater extremes.

But invoking the “arms race” seems a lot more convincing when you are talking about out-and-out evolutionary combat. The second type of sexual selection, “male-male competition” is all about the escalating evolution of better and better weapons. In some species, males actually fight for sex, as with these male elephant seals battling for control of a harem of females. But in other species, it’s enough to look big and scary, to intimidate the other guy before he even tries to fight you. If your antlers are large, you might fight other males and win. But if your antlers are humongous?  You could be king of the lek without ever having to tangle. Possible bonus: Your “armament” may also serve as an “ornament” if females find your big antlers sexy. These University of Minnesota researchers found that lion’s manes did double duty, attracting females AND intimidating other males.

Wade’s Science Times article profiled a recent review paper on the diversification of male animal “weaponry” by Douglas Emlen at the University of Montana.

Dung beetles -- from a nice Discover Mag blog posting about the evolution of female dung beetle horns.


For your viewing pleasure, the piece focuses especially on the dramatically beautiful “horns” of dung beetles. And, as in most profiles of sexy science, Wade could not resist taking the next step, pushing toward that ultimate climax of sexy science.

What’s sexier than sex and warfare?

Sex and warfare and humans, of course:
“People have pathetically puny teeth and claws compared with the armaments of other dominant species. This is a sign not of pacific intent but of the fact that they manufacture their weapons.”

In other words, the “arms race” is more than just a metaphor that allows us to comprehend the evolution of elaborate organic weaponry on our own terms, those of technological weaponry. It’s an analogy between human and nonhuman evolved features.

If you read what I wrote about analogies last week, you’ll know that when evolutionary biologists posit such an analogy, they are claiming that evolved tusks and manufactured guns were generated in response to the same selective pressures. They have different evolutionary histories–in this case, the difference is even more extreme, since one has a biological evolutionary history and the other has a cultural evolutionary history.  But they are analogous because they share an adaptive function.

I am most fascinated by analogies like these, which effectively blur the boundary between biological evolution and cultural evolution. But it’s not just the boundary between biology and culture that becomes a bit blurry here. Wade interviewed a primatologist who claimed that it’s “very reasonable to assume that, as humans evolved and our culture became more complex, skills in tool making or other cultural behaviors took over from anatomical traits as ‘markers’ of a male’s competitive skill.”  In other words, the proposed mechanism for such a shift is also kind of hazy.  Claiming that cultural evolution just “took over” from biological evolution is not exactly a substitute for a testable hypothesis.

In any case, whether or not you think this is a reasonable assumption, you have to admit that it’s very compelling. Analogies are compelling—that’s why they are so useful.  They motivate us to make analytical leaps that, in the best of scientific circumstances, may also be empirically verified.

Sometimes those gravity-defying leaps also defy logic, however. Even a seasoned science journalist like Nicholas Wade may be seduced by sexy analogies into making such a logic-defying leap.

Wade analogizes between the organic “weaponry” featured in Dr. Emlen’s paper and a samurai helmet or a crossbow. So far, so good—these could make sense within the context of sexual selection.

Then, suddenly, Wade leaps into the geopolitical domain of the “menacing tanks and rockets that paraded through Red Square in Moscow in the days of the Soviet Union.” This is where the allure of the arms-race analogy becomes dangerous. Was the Cold War a result of sexual competition? Is the “the advent of chemical, biological and nuclear arsenals” really relevant to a piece on male-male competition?

The arms-race analogy has been scientifically productive, helping biologists imagine a series of evolutionary interactions that mimic the military escalation of the Cold War.  But when it leads us to relate sexual selection to global politics, it has probably overreached the limits of its utility. And when this overreaching happens on the cover of the Science Times, we must take pause.

Evocative analogies are powerful tools and—just like that nuclear arsenal—they should be used only with the greatest of caution.