Thursday, March 23, 2006

Do You Feel Lucky, Pan sapiens?


There are a lot of reasons to be baffled by the renewed attacks on the theory of evolution(1), but I'm particularly bemused by the denialists' contention that the theory is a dangerous dogma. It's true that there's no shortage of dull-witted biologists who can be too stubborn in their pronouncements, as unwilling to consider a dissenting perspective as the loudest denialist(2), but any scientist worth her salt - or, for that matter, any informed, reasonable individual - realizes that the theory of evolution is, itself, evolving. Sure, some scientists can be dogmatic, but the theory in question is not a dogma. It is adaptable.

When most of us hear the word, evolution, crude caricatures of chimpanzees, Neanderthals, and walking fish-reptiles come to mind. Sometimes, we may even think of diagrammed cell division or an eukaryote propelling itself by means of rudimentary flagella. Yet rarely, if ever, do we consider change at the molecular level. Biophysicists Harold Morowitz, of George Mason University, and Eric Smith, of the Santa Fe Institute, do exactly that, suggesting that a "central set of chemical reactions has been in place since life's earliest moments about four billion years ago." Journalist Joel Achenbach explains the Morowitz/Smith hypothesis in a recent National Geographic piece, "The Origin of Life...Through Chemistry."
"These reactions involve just 11 small carbon molecules, such as citric and acetic acids, very ordinary stuff that would have been abundant on the young Earth. Those 11 molecules could have played a role in other chemical reactions that led to the development of such biomolecules as amino acids, lipids, sugars, and eventually some kind of genetic molecule such as RNA."
What makes the hypothesis so fascinating, though, is the suggestion that survival of the fittest or, more accurately, natural selection, occurs at the molecular level. Acenbach clarifies: "Some types of molecular chains outcompeted other molecular chains for the planet's resources, and gradually they led to the type of molecules that life depends upon - all this before the first living thing oozed forth." Wow! It seems obvious, really. Of course molecules compete in the same way genes do.

Unmentioned in the Geographic article is the divide between Millerites, evolutionary biologists who stand by Stanley Miller's mid-twentieth century hypothesis that life began at surface level, when electricity, atmospheric gases, and water interacted in such a way as to form the oft-mentioned biotic soup, and ventists, the scientists who feel such a soup was more likely arrived at on the ocean's floor, a by-product of interactions involving pressure and heat near hydrothermal vents. (I prefer to think of the two perspectives as the Frankenstein approach (electricity) and the oven hypothesis (hydrothermal) and, although I remain uncertain of which I "support," when the two camps duke it out the Frankenstein approach always seems to be forced back against the ropes.) Morowitz and Smith are ventists. Will their molecular metabolism hypothesis, viable both on the surface and under the sea, come under fire from Millerites because they are "the enemy"?

Such language - "duke it out," "the enemy" - is hyperbolic, but most folks would be shocked by how nasty the debates in the halls of evolutionary biology can become. Whatever impression the more extreme denialists seek to convey (e.g., Darwin was a blasphemer who today inspires countless secularists, marching in lockstep, to carry on his unholy work), the theory of evolution is anything but settled. Darwin's theories provide a spring board, an introduction, but are not fast. As with most revolutionary science, Darwin's ideas raise a host of questions.

One of these questions, in particular, has plagued biologists ever since Darwin's theory was first published. Commonly referred to as the "paradox of evolution," it asks, how can we reconcile evolutionary variation - all the shapes, colors, sizes, etc. - with the limited number of structures and systems all species share? The two readily observable realities seem contradictory: unlimited diversity produced by a limited system. Marc Kirschner, chair of the Systems Biology Department at Harvard Medical School, recently proposed a novel answer, facilitated variation. I turn to Robin Marantz Henig's article, "Resolving Evolution's Greatest Paradox," in the March/April 2006 issue of New York Academy of Sciences Update.
"Kirschner used an analogy borrowed from the kindergarten classroom to explain how his and Gerhart's theory differs from evolutionary theory up to this point. Traditionally, he said, biologists have compared life to a lump of modeling clay, 'incredibly plastic, and able—due to the accrual of many small changes—to go in any direction.' But this is the wrong metaphor, he said. In truth, life is more like a bunch of Lego blocks. As with Legos, the basic building blocks of biology are rigid and quite similar to one another, but 'there is a large variety of structures that can be assembled from similar parts.'

Another way of looking at it, Kirschner said, is to try to imagine trying to get a monkey to write the word 'MONKEY.' You could do so by giving the monkey a pen and paper, but that would never work—all you'd get would be 'random lines and scratches.' But if you gave him a typewriter, then you might be getting somewhere. It would take a very long time (Kirschner calculated about ten years, typing at the rate of one keystroke per second round-the-clock), but the monkey would eventually produce all six letters in the right order, because the typewriter restricts the results of his physical actions—always letters instead of scribble-scrabble. 'Letters have at least a chance to be useful,' Kirschner said. 'Most pen scratches do not.'

If, instead of a typewriter, the monkey was pounding on a computer keyboard programmed with an automatic spelling corrector, the time it would take for him to type out the word 'MONKEY' would be reduced dramatically, from ten years to probably less than a single day. 'More constraint equals more useful outcomes,' Kirschner said."
OK. That's clear, but how can the spell checker analogy account for so much complexity and variation?
"Complexity in multicellular organisms—changes and refinements in beak shape, pigmentation, jaw structure, limb formation—can be explained, he said, by forces involved in 'changing the time and extent of a process rather than creating a new process.'...[This] helps account for the surprising fact that the human genome isn't much bigger than the genome of a frog or a fruit fly. The vast differences among these organisms are accounted for not by number of genes, he said, but by how the genes are expressed...In other words, the gene itself doesn't have to be different; what changes is the timing or location of the gene's expression."
Beautiful! One need look no further than the gestation of a human embryo to get a sense of how facilitated variation works, each step recalled and repeated, generation after generation, the species' genome receiving new information all the while. The same "program" is "running" inside frog eggs or the squirrel's womb.

Still, it's important to note that facilitated variation is but a piece of the ever-changing puzzle, no more or less important than punctuated equilibrium or the notion of spandrels. Moreover, though a lovely marriage of genetics and natural selection, Kirschner's theory is less applicable when considering a restricted time line.

"Global Warming Fuels Speedy Evolution," a piece by Larrry O'Hanlon (Discovery News), provides readers with a number of recent, documented cases of dramatic changes in animal phylogeny. Within the past seven years, the cane toad (Bufo marinus) population in Australia - an introduced, destructive species - has evolved longer legs, an adaptation that has made the species considerably more mobile, enabling them to more quickly expand away from the introduction point. Longer legs equals more ground covered which, in turn, means access to virgin territory and plentiful food. In short, further colonization. Not surprisingly, some native Australian snake species viewed the new arrivals as prey. After swallowing the amphibians, however, these reptiles would ingest the toad's toxin and - pardon the pun - croak. Amazingly, in the same seven-year window, these snake species have, via natural selection, developed smaller jaws, thereby preventing them from eating the toads and ingesting the toxin. All this change in seven years and across several unrelated species!

Invasive species aren't the only reason for accelerated, or rapid evolution, as it is officially called. Global warming (better termed climate change) is a prime mover, too.
"Research on toads, frogs, salamanders, fish, lizards, squirrels, and plants are all showing evidence that some species are attempting to adapt to new conditions in a time frame of decades, not eons, say biologists. What's more, one of the biggest reasons for all this evolution right now may be that human-induced changes to climate and landscapes give species few other options....The first known case of a mammal responding genetically to warmer climate warming is the red squirrel of the Yukon Territory. Canadian scientists have discovered that red squirrels are giving birth about 18 days earlier than their great-grandmothers. It's the early squirrel that gets the nut, after all: natural selection in action. 'Climate change is going to be a massive agent of evolution,' said ecologist and rapid evolution researcher David Skelly of Yale University."
Rapid evolution provides more evidence for the punctuated equilibrium hypothesis, suggesting that, when need be, species have the ability to adapt much more quickly than paleontologists, geneticists, and evolutionary biologists originally believed possible. The gaps in the fossil record, so often highlighted by denialists as proof of evil-ution's failings, are easily accounted for when we observe, in the space of just one decade, significant phylogenetic changes within a given population.

All of these observations and new hypotheses are very exciting to me, but I realize a portion of the folks reading Hungry Hyaena, maybe even the majority, find this round-up rather esoteric. I thought it only sensible, then, to wrap up by bringing evolution closer to home or, in this case, closer to man. Biologist Soojin Yi (Georgia Institute of Technology, Atlanta) recently confirmed that both species of chimpanzee (Pan troglodytes and Pan paniscus) are more closely related to humans than previously assumed. In fact, as I've argued often, it looks as though the taxonomy will have to be changed. Homo sapiens will no longer be alone in the genus; Homo troglodytes and Homo paniscus will soon be joining our private party!

I hope this announcement will provide a reality check for our unfathomable human hubris, but, as incredibly happy as I am about it, I'm not altogether satisfied about where it will lead. As I see it, humans should move genus, not chimpanzees. Our species should be dubbed Pan sapiens. In other words, we should willingly discard our crown and step down to join the great unwashed, honest at last when regarding our reflection. I'm not alone in feeling this way. Andrew Rambaut, an evolutionary biologist at Oxford University, says, "It seems a bit human-centric to want to put chimps into the 'Homo' genus and not reclassify humans as 'Pan.'" Jared Diamond, the acclaimed author of Guns, Germs, and Steel and, more recently, Collapse, wrote an excellent, lesser known book in 1991, titled, The Third Chimpanzee, in which, among innumerable salient points, he suggested we do away with the arbitrary Homo delineation. After all, every ape relies on the same damned spell checker.

(1) Some folks refer to intelligent design as "the fourth wave" of resistance. The first wave of opposition dates back to the 1860s, when the theory was nascent and controversial. The second wave, during the 1920s, culminated with the Scopes Trial. Then, in 1987, the Supreme Court ruled against mandatory teaching of creation science - Edwards v. Aguillard - effectively putting an end to the third wave.

(2) Reading "Evolution In Action" (Sid Perkins, Science News, Feb. 25, 2006), I was struck by the us-versus-them tone prevalent throughout the article. The reactionary posturing of some scientists - and, in this case, a science journalist - can take on a disturbing tone: "From 2001 through 2003, anti-evolution activity was reported in 40 states." Anti-evolution activity? Reported? The witch-hunt has begun!

Photo credit: Ripped from brainfuel.tv

4 comments:

Miranda said...

While the debate over the theory is a good thing in my book, I am continually baffled-- open mouth and all-- with the debate over the man. Recently I attended a lecture at AMNH, where a panel of four professionals in opposing camps presented on Darwin’s continued legacy. Philosopher Michael Ruse started his power-point presentation with a listing of the top three things that have hindered the progression of the theory of evolution. While numbers one and two were expected, number three was not: 3. Ronald Numbers. This gentleman happened to be both the resident creationist, and the next speaker. These underhanded digs continued throughout their respective presentations, and through the question and answer period, which got nasty. Has Darwin’s legacy gotten so muddied with these renewed attacks that we are unable to see him behind the published authors claiming to know him best?

I feel that an attack on the theory is one thing (albeit not my thing), but this lecture undermined the legacy that the presenters claimed to be advancing. And there was even a fancy moderator…

Hungry Hyaena said...

Your description of the "lecture" sounds par for the course these days. It's a shame, really, as the science itself continues to develop in the most exciting of ways. Eventually, the legacy of the man will be sorted out, though he is destined to be considered even more of an iconoclast, perhaps in the same way Che Guevara is/was.

I do my part by dutifully carrying my "Darwin Has A Posse" tote bag to the video and grocery store. (http://www.cafepress.com/darwinposse)

Pisces Iscariot said...

I find it amusing that those who expound 'intelligent design' actually disprove the theory by their own ignorance.
An absurdity similar to those who attempt to prove the existance of God by quoting the Bible.

prairieoyster said...

I just found your blog. Really interesting! My comments are totally an aside (sorry!), but I was struck by the mention of Ronald Numbers.

I interviewed Ronald Numbers years ago as an undergrad for a Anthropology project. The intent of the project was to see how faculty versus undergraduates felt evolution and creationism should be presented in class. We were referred to Numbers by his wife, a faculty member in Zoology and a reasonably well-known physical anthropologist. He gave us a very nice interview about the history of evolutionary theory. I honestly had no idea about his actual leanings!! I never followed up on his work!

At any rate, we had some interesting points brought up in the interviews. Not surprisingly, most faculty felt it beneath them to mention creationism at all. What ended up being more eye-opening was the response by students who had been raised creationist. Although most of them now accepted evolution as sound science, they had a difficult time because they were embarrassed by those faculty who ridiculed the beliefs they had been raised with. They were less likely to feel welcome to participate in biology or physical anthropology because they didn't want to come off as ignorant.

That insight has had a big affect on the way I teach evolution (granted as a grad student adjunct). I honestly don't think there is anything MORE important in an introductory biology course than integrating every student's viewpoint in the discussion. Or at least give them the opportunity to disagree... as long as they can prove they're thinking critically.