Oh, the allure of a misleading headline. When I saw this story on BBC news, “Mammoths had ‘anti-freeze blood’, gene study finds,” I thought for a moment that scientists had discovered those Ice Age behemoths had secreted some glycerol-like compound into their tissues to prevent freezing. Such a finding would have been genuinely astounding because, as far as I know, that trick is seen only among certain polar fish and overwintering insects; it would have been a first among mammals.
In reality, the surprise is not that the mammoths’ blood resisted freezing but rather that it cleverly continued to do what blood vitally must do: transport oxygen to needy tissues, even at low temperatures. Kevin L. Campbell of the University of Manitoba and his colleagues reached this conclusion through a nifty piece of paleogenomic molecular biology, as they reported in Nature Genetics. Their technique’s fascinating potential to help biologists learn about the physiologies of extinct creatures has already drawn considerable attention, but the mechanism of the hardiness of the mammoths’ blood also helps to highlight a common way in which evolution innovates.
Mammoths display obvious features that must have helped them stay warm in the brutal subzero temperatures of the Pleistocene ice ages, such as long, shaggy coats and small ears. They may well also have had less obvious ones, too, like the arrangement of blood vessels in the legs of caribou that allows countercurrent exchange to minimize the loss of body heat from their legs while they stand in snow. Nevertheless, Campbell had wondered about whether the mammoths’ blood might have been adapted, too, because of hemoglobin releases oxygen into tissues only sluggishly at low temperatures.
Human hemoglobin. By Richard Wheeler (Zephyris) 2007.
By extracting the hemoglobin gene from DNA in well-preserved mammoth remains and inserting it into bacteria, Campbell and Alan Cooper of the University of Adelaide were able to replicate samples of the mammoth’s hemoglobin. And sure enough, in subsequent tests, the resurrected hemoglobin proved to release oxygen much more consistently across a wide range of temperatures—even glacially low ones.
Perhaps it sounds surprising that something so fundamental to mammalian physiology as its hemoglobin chemistry would be subject to evolutionary revision. Surely the mammoths might have survived the cold just as well by evolving more hair or thicker insulation. Yet hemoglobin chemistry is actually a feature particularly well suited to modification—and that has been modified many times throughout evolutionary history. The key is that the genes making the globin proteins have leant themselves to frequent duplication throughout evolutionary history, which opens up the opportunity of variation among the copies and specialization in their activities. Read more
"Chiroptera" from Ernst Haeckel's Kunstformen der Natur, 1904
A recent discovery about the evolutionary origins of bats relates, at least indirectly, to a problem causing the extinction of many bat species throughout North America.
As they reported in the Proceedings of the National Academy of Sciences, Ya-Ping Zhang of the Kunming Institute of Zoology and colleagues have found evidence that mitochondrial genes in bats, which are responsible for their metabolic use of energy, have been under heavy selection pressure since early in their evolutionary history. Such a conclusion makes considerable sense on its face because bats’ way of life is highly energy intensive.
Nevertheless, the finding also helps to sketch in some of the mysteries of the evolution of bats. Bats are hard to look at in fossil record because they don’t fossilize well; they suddenly appeared in Eocene strata from about 50 million years ago looking fairly much as they do now, which left cryptic some of the steps up to that point.
Over the past decade, several discoveries have helped to firm up the view that the ancestors of bats spent their lives leaping and hopping through vegetation before they could fly; that the evolution of their wings seemed associated with key changes in certain genes for digits; that their ability to echolocate seems to have emerged after their capacity for flight; that the larger bats called Megachiroptera are indeed descendants of the smaller Microchiroptera and not the convergently evolved cousins of primates. The place of the metabolic changes in that scheme, though, were largely speculative. The demands on bats’ mitochondria could have emerged only once they started flying, but instead it seems that their ancestors made a living as an extra hyperkinetic group of insectivores leaping through the trees and shrubs.
All that energy expenditure comes at some cost to the bats, however. Most obviously, they need to eat colossal numbers of insects to satisfy their energy needs. During the cold winter months when insects become more sparse, bat species that don’t migrate to warmer climes must overwinter in caves, suspended in a state of torpor with their metabolisms at a crawl.
Smack your heads in shame, my fellow intellectual snobs of the Northeastern elite. We’re used to sneering at the creationist follies playing out in Kentucky, Pennsylvania, Texas and elsewhere—benighted hellholes where they wouldn’t know a decent bagel, a proper chowder or the correct pronunciation of “Worcester” if it were served up alongside their customary daily ration of cheese grits. But now the same buffoonery is occurring in (bless my nutmeg!) Connecticut.
In short, the administration of the Weston Intermediate School has twice rejected a proposal for students in the third, fourth and fifth grade Talented and Gifted program to study the work of Charles Darwin. Such a plan seems to be completely in keeping with Connecticut’s standards for science education. Mark Ribbens, the principal who first denied the plan, apparently left the school earlier this year, but a subsequent resubmission for the curriculum fared no better.
Brandon Keim at Wired Science has more details, but I’m struck by the proposition (which may not originate with Brandon) that this antievolution development in Weston is somehow different in kind from what we’ve seen before:
Evolution education is under attack in Weston, Connecticut, but not from the usual direction.
Nobody is promoting intelligent design in the curriculum, or asking schools to teach evolution’s “strengths and weaknesses.” There’s just an administration afraid that teaching third graders too much about Charles Darwin will cause trouble.
How does this genuinely differ in essence from the reasons usually given by evolution’s opponents in education? No matter whether they attack evolution’s merits directly or insist that intelligent design should be taught as a valid alternative, the antievolutionists nearly always say that “forcing” evolution on students would intrude on parents’ rights to raise their children as they see fit. In other words, they are saying not to create controversy and upset the parents. And just as seems to be the case here in Connecticut, the antievolutionists often make these arguments preemptively, long before any actual outrage from parents appears.