Extinction is evolution

I often enjoy Olivia Judson's science blog on NYTimes.com. She has an actual science background, and gets the science badly wrong far less often than most other reporters of science.

Her most recent post is more in line with what I expect from science journalism. Without recapping her whole argument, she writes, "But if [evolution] has that much potential — how come organisms keep going extinct in nature? In other words, why does evolution keep failing?"

She then goes on to make a big deal about how evolution fails each time a population fails to evolve. But in so doing she fails to admit the distinction between evolution on the one hand and adaptation on the other.

Evolution is genetic change in lineages with time. Adaptation is the process by which the genetic makeup of a population is altered in a way that helps individuals of that population be more successful in their environment. Adaptation is one mechanism, and result of, evolution. It happens to be the best known mechanism, and the one that in the popular imagination defines evolution. But evolution has lots of other mechanisms. Genetic drift for example. Imagine you have a small population of squirrels on an island, some gray, some black. A disease comes through and kills a significant portion of the squirrels, and even though they are all equally susceptible to the disease, through the randomness of epidemiology more grays than black catch it and die. After the disease, the population has a higher proportion of black alleles than before. The population has evolved, because the proportional genetic makeup of the population has changed. But this is not an example of adaptation, because the genetic change was not caused by one version of the color gene conferring a selective advantage over the other. The allele frequencies "drifted" without being pushed by selective considerations. The next time the disease comes though more black squirrels could happen to catch it, and the allele frequencies could drift back.

So adaptation is not the be all and end all of evolution. Much of the evolution that happens is non-adaptive. And another important mechanisms of evolution is extinction. Imagine now that the disease killed not just some, but all of the squirrels on the island. That population is extinct. They are no longer represented in the genetic diversity of squirrels more generally, of rodents more generally, of mammals more generally. The remaining diversity, through the removal of that population, has changed. The extinct population has ceased evolving, but through their removal the larger group is left genetically less diverse. The genetic makeup of the larger lineage has changed, so evolution has occurred. It is also possible that the residual populations are more fit than the pre-epidemic average, because they are resistant to that particular disease. Whether or not this qualifies as adaptation depends on the fine details of the definition of adaptation you prefer. There is no standardly accepted definition, or rather different groups of biologists prefer different definitions. But all evolutionary biologists, save those who have crossed over into journalism, agree that extinction is an example of, not a failure of, evolution.

Global Amphibian Declines call for frog costumes.

There are few, if any, taxa losing species diversity as quickly and thoroughly as the amphibians.

From amphibiaweb.org:

"Amphibians, a unique group of vertebrates containing over 6,200 known species, are threatened worldwide. A recent assessment of the entire group (globalamphibians.org) found that nearly one-third (32%) of the world’s amphibian species are threatened, representing 1,856 species. Amphibians have existed on earth for over 300 million years, yet in just the last two decades there have been an alarming number of extinctions, nearly 168 species are believed to have gone extinct and at least 2,469 (43%) more have populations that are declining. This indicates that the number of extinct and threatened species will probably continue to rise (Stuart et al. 2004)."

And this is almost surely an overly optimistic view. The thousands of species for which we have no data are not considered threatened, and an unknown number of others, likely in the hundreds, has gone extinct without ever being discovered.

Amphibian lineages that have existed for tens of millions of years are ending shockingly quickly. The factors that are killing off these ancient groups are all the works of humanity: pesticides, industrial pollutants, introduced species and diseases, habitat destruction and alteration and rapid climate change. There is no reasonable doubt but that we have driven the rate of amphibian extinction to several thousand times its natural rate. We could barely kill them off more quickly if we tried. Genocide is not too strong a term.

Amphibians are widely seen as indicator species. Healthy ecosystems have healthy amphibians. Indications are poor.

So to help raise (the currently abysmally low) awareness of the scope of amphibian declines, Iris and I have decided to walk Bay to Breakers wearing homemade from costumes. And we hope to organize a group of friends and colleagues to walk with us, similarly garbed. A costume recognizable as an amphibian, or even a shirt with amphibian pictures on it. Perhaps we will hand out informational pamphlets to people who ask what we are about. If you are interested in joining us, please email me.

20,000,000 years of evolution, killed as bycatch

" First human-caused extinction of a cetacean species?"

Abstract from Biology Letters:
"The Yangtze River dolphin or baiji (Lipotes vexillifer), an obligate freshwater odontocete known only from the middle-lower Yangtze River system and neighbouring Qiantang River in eastern China, has long been recognized as one of the world's rarest and most threatened mammal species. The status of the baiji has not been investigated since the late 1990s, when the surviving population was estimated to be as low as 13 individuals. An intensive six-week multi-vessel visual and acoustic survey carried out in November–December 2006, covering the entire historical range of the baiji in the main Yangtze channel, failed to find any evidence that the species survives. We are forced to conclude that the baiji is now likely to be extinct, probably due to unsustainable by-catch in local fisheries. This represents the first global extinction of a large vertebrate for over 50 years, only the fourth disappearance of an entire mammal family since AD 1500, and the first cetacean species to be driven to extinction by human activity. Immediate and extreme measures may be necessary to prevent the extinction of other endangered cetaceans, including the sympatric Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis)." (emphasis mine)

BBC coverage