October 30, 2008

Land of the Lemurs And Other Lessons In Practical Evolution

Last night, I went to class with The Wife. Instead of a regular English composition class, there were four half-hour lectures about Charles Darwin and applications of his ideas in science. Well, there were supposed to be. The first lecture wound up being kind of about climatology and kind of about important figures in the environmental movement and kind of about, well, I don't know what it was about.

But the other three were quite interesting. The Wife's professor gave the most creative performance, with a Disney video (query if copyright was violated), a reading from Barbara Tuchman's A Distant Mirror, and a prose reading of the professor's own composition, all relating to the Bubonic Plague. My critique here was that the emotional impact of the content -- the Tuchman passage is one of the most compelling in popular history, and the professor's story was pretty damn scary, too -- overshadowed the insight that the plague as it it exists today is different than the plague as it existed in the fourteenth century. And interestingly, pockets of humanity developed resistances to it; the plague spread to Bohemia but did not take very many victims there. Bohemian people today are also much more resistant to other diseases like HIV.

Anyway, the modern plague bacterium, yersina pestis, is different from its fourteenth-century ancestors in that it now kills its human host much more slowly. Where there were cases of healthy people dying overnight, doctors attending to their patients dying before their patients did, and corpses piling up like cordwood in shallow graves, today the modern plague victim begins to feel flu-like symptoms and does not show buboes for nearly a day. After that, it takes another two to three days before the bacteria begins to seriously assault internal organs and contaminate the blood. This gives the victim time to seek medical help and antibiotics, which is what the professor did after developing plague-like symptoms while observing prairie dogs and birds in New Mexico.

So what has happened in seven hundred years? Well, thirty generations of humanity and something like thirty thousand generations of yersina pestis have adapted to one another. Since much more opportunity to evolve has taken place on the bacterium side, it seems likely that this is where the bulk of the adaptation has taken place -- the plague bacterium today has "learned" to work slower, so as to give its host more time to come in contact with other potential hosts and spread the organism around so as to breed better. By being less virulent, the bacterium has survived better.

Humans, too, have adapted better survival techniques, although in our case this manifests in technology and behavior rather than profound biological change. But we cannot rule out the fact that for people of Asiatic, African, or European descent, we are all by definition descendents of people who survived the plague, and therefore we are more resistant to it than those poor souls who died of it. The plague weeded out those members of the human population who did not have the resistance and left the population better-adapted to resist the disease.

So that Darwinian lesson was kind of lost in the terror and horror that this particular interaction of parasite and prey evokes. But the lesson is still there.

The third speaker was easily the most charismatic and he had a very charismatic subject -- top-of-the-pyramid predators. These are in many cases some of the most beautiful animals out there and their activities are some of the most dramatic in nature. In particular, the focus was on the re-introduction of grey wolves into Yellowstone National Park and the surrounding areas. Gray wolves had been eliminated from that ecosystem in the 1930's, but in the late 1990's, about thirty wolves were captured in British Columbia and re-introduced into the Yellowstone. They've done well there, although in the five or six generations since introduction, many of their descendants have developed black fur instead of gray. No one is quite sure why.

More interesting than that, though, was the big concept that the speaker -- the curator of a natural history museum in Cody, Wyoming -- took the lesson to. In the midst of some spectacular photographs of the Yellowstone area, he was able to show that the re-introduction of these top-level predators had effected a cascade of changes in the area. The wolves mainly prey on elk, which expands the availability of grazing land for moose (who, unfortunately, are still feeling the effects of the great fires of 1988). The elk population has done just fine, producing larger specimens. The elk have learned to be more vigilant while grazing themselves, and have adopted social patterns of posting sentries while the herd is feeding. They have also avoided certain areas where they feel more vulnerable, and in those areas, aspen and willow trees are returning -- previously, those sorts of trees had not been doing well for fifty years or so in the park. Now, the elk are avoiding the stands of young aspen because aspen grow in areas that wolves like to hunt, and not eating them while they are still saplings. So, aspen are returning to Yellowstone and that is good for different species of bird. The return of willow trees is also good for beaver, who have returned to use this renewed building material. But the big losers have been the coyotes -- they have had to give up a lot of territory to the wolves and have been the victims of wolf attacks. The wolves attack the coyotes not for food but rather to eliminate competition, and coyotes have abandoned their behavior of hunting live prey and are making their living by scavenging and living closer to human areas (which wolves try to avoid).

Now, a lot of this adaptation is behaviorial. But the point is that nature adapts very quickly to the change. And some of the adaptations do produce physical changes -- the bigger elk, the darkening of the wolves' fur. The species that are best-equipped to adapt to the new environmental factor (the presence of the predators) thrive, like the beavers and the aspen. Ohters who have more difficulty adapting dwindle in numbers, like the coyotes.

The last speaker discussed his trip to Madagascar and his observations of lemurs on the world's fourth-largest island. He was, unfortunately, not a very charismatic speaker, but he could have made the most compelling case for evolution and its study of all of them. The raw materials were certainly there.

What it boiled down to was that the fossil evidence suggests that a single raft of lemurs somehow made it from the mainland of Africa to Madagascar about 40 million years ago. Genetic markers in modern-day lemurs indicate that every lemur on the island has a single common ancestor -- there may only have been one female on that raft. Since then, lemurs have flourished on Madagascar (unlike on the mainland where they were displaced by monkeys and are now largely extinct). Madagascarian lemurs come in a wide variety of shapes and sizes. There are mouse lemurs, giant lemurs, furry ones, long-tailed ones, short-tailed ones, ones with bat-like skin flaps, ones with long claws, short claws, big eyes and little eyes, and the list goes on and on. These cute little critters have adapted to all sorts of ecological niches and developed into at least forty different species.

The story goes that Darwin very much wanted to land on Madagascar on the return voyage of the HMS Beagle, but was overruled by the captain. The professor made the case that had Darwin been able to observe lemurs (and other animals) on Madagascar, he would have found them an even better study in adaptation by natural selection in the lemurs than he did with the finches and tortoises in the Galapagos.

The science was fascinating. The speakers were of varying quality, but that's what you get sometimes. Mainly, the engagement with scientists and their work was the profit -- and the pleasure. You can do things like this too. Universities and museums all over the world are doing a variety of special presentations and exhibits and such to celebrate Darwin. The 150th anniversary of the publication of Origin of Species was a few months ago, and his 200th birthday will be in Februrary of 2009. I encourage all of you Readers to find these events in your area and learn more.

2 comments:

Orange Phantom said...

Just a thing I noticed concerning evolution..
all of the examples you gave related to adaptation. Fur turning from grey to black is not evolution. The different species of lemurs are still and will always be lemurs. Speciation is very common, and not to be confused with evolution.

Transplanted Lawyer said...

No. Speciation is evolution. For that matter, so is adaptation. Adaptation is how evolution works.

At least you now concede that speciation does occur, which is more than you've done in the past. So we are making some progress.