Mexican Cave Scorpions Put a Dent in Dollo's Law

Monday, March 15 10:26 am

Typhochactas mitchelli is among the smallest known scorpions and part of the Typhlochactidae family of cave scorpions, endemic to Mexico. Like all scorpions, it fluoresces in long-wave ultraviolet light as this image of its ventral side highlights. Credit: V. Vignoli

Blind scorpions that live in the stygian depths of caves are throwing light on a long-held assumption, showing that specialized adaptations aren’t always an evolutionary dead-end. Looking at the phylogenetic relationships among species of the scorpion family Typhlochactidae, endemic to Mexico, Associate Curator Lorenzo Prendini and colleagues found that species currently living closer to the surface (under stones and in leaf litter) evolved independently on more than one occasion from specialized deep-cave ancestors adapted to life further below the surface (in caves). This finding puts a dent in both Cope’s Law of the unspecialized, which assumes that novel evolutionary traits tend to originate from a generalized member of an ancestral taxon, and Dollo’s Law of evolutionary irreversibility, which theorizes that specialized evolutionary traits are unlikely to reverse.

Scorpions are predatory, venomous, nocturnal arachnids related to spiders, mites, and other arthropods. About 2,000 species are distributed throughout the world, but only 23 species found in ten different families are adapted to a permanent life in caves. One of these families is the Typhlochactidae, comprising four genera and nine species.

“Scorpions have been around for 450 million years, and their biology is obviously flexible,” says Prendini. “This unique group of eyeless Mexican scorpions may have started re-colonizing niches closer to the surface from the deep caves of Mexico after their surface-living ancestors were wiped out by the nearby Chicxuluxb impact along with non-avian dinosaurs, ammonites, and other species.”

Alacran tartarus, also in the family Typhlochactidae, has been found at the greatest depth of all scorpions, at 750 to 920 meters below the surface in the Sistema Huautla, Oaxaca, Mexico. Credit: P. Sprouse and A. Gluesenkamp

After Darwin at AMNH: Ian Tattersall

Thursday, February 04 5:26 pm

Curator Ian Tattersall on Darwin’s Thoughts About the Fossil Evidence for Human Evolution

Scientists at the American Museum of Natural History continue to celebrate the 200th anniversary of Charles Darwin’s birth and the 1859 publication of On the Origin of Species with a collection of vignettes describing expeditions and ideas with links to Darwin’s seminal work.

Below is an excerpt of a longer piece that Ian Tattersall wrote for Evolution: Education and Outreach in 2009.

Charles Darwin was curiously unforthcoming on the subject of human evolution as viewed through the fossil record, to the point of being virtually silent. He was, of course, most famously reticent on the matter in On the Origin of Species, … [and] this is true even of his 1871 book The Descent of Man, and Selection in Relation to Sex in which Darwin finally forced himself to confront the implications of his theory for the origin of humankind [but in which he barely managed even a passing reference to the Neanderthal fossil that by then was the subject of extensive scientific speculation.]

There were…many reasons why Darwin should have been disposed in The Descent of Man to shrink from any substantive discussion of whether extinct human relatives might actually be represented in fossil form. The fossil and antiquarian records were awash with fakes; any discussion of human ancestry was rife with social and political pitfalls; and anyway, by his own close colleague’s testimony, the record contained nothing that could have any relevance to ancient and now-extinct human precursors. Add to that Darwin’s innate suspicion of the distorting effects of incompleteness in the fossil record, and he may have felt that a large degree of discretion on the matter was mandatory.

The Feldhofer skullcap--the Neanderthal type specimen-- was discovered in a limestone cave in 1857 and is one of a handful of fossils that Darwin could have been aware of while writing The Origin of Species. The image includes an associated zygomaticomaxillary fragment that was discovered in the miners’ dump almost a century and a half later, in 1997. Credit: AMNH

None of this means, of course, that The Descent of Man has not exerted an immense influence on the sciences of human origins over the last century and a half. Just as it is easy for English speakers to forget how much they owe to William Shakespeare for the language they use daily, we tend to lose sight of the fact that much received wisdom in paleoanthropology has come down to us direct from Darwin. Darwin it was who proposed a mechanism for the structural continuity of human beings with the rest of the living world and who gave a detailed argument for human descent from an “ape-like progenitor.” It was Darwin who documented beyond doubt, in The Descent of Man, that all living humans belong to a unitary species with a single origin—which we now know, on the basis of evidence of which Darwin could never have dreamed, to have been around 200,000 years ago. He also had the inspired hunch that our species originated in the continent of Africa—and again, this guess has been amply substantiated by later science. Darwin’s perceptions on the behaviors of other primates and how they relate to the way humans behave were remarkably astute, particularly given the highly anecdotal nature of what was then known. Read more »

Previous Museum Podcasts

Thursday, May 14 3:41 pm

Michael Pollan: In Defense of Food

Starting with his best-seller, The Botany of Desire: A Plant’s Eye View of the World, Michael Pollan has uncovered hidden aspects of the industrialized American diet. In his newest book, he encourages us to take control of our eating habits with a simple resolution, “Eat food. Not too much. Mostly plants.” Michael Pollan discusses ways of doing this with Peter Hoffman, chef and owner of Savoy. Recorded on May 14, 2009.

Download | RSS | iTunes (55 mins, 53 MB)

Global Kitchen: Climate Change and Coffee

Todd Carmichael, La Colombe Torrefaction; Coffee Roasters & Blenders; and Danner Friedman, Rainforest Alliance, discuss growing coffee amid the realities of climate change. Learn how the coffee you purchase can help protect against deforestation, one of the leading causes of carbon dioxide emissions. A coffee cupping introduces several coffee varietals (plant strains) grown under different environmental conditions, from slash-and-burn farms to rainforests. Recorded on February 3, 2009.

Download | RSS | iTunes (1hr 16 mins, 70 MB)

Is God a Mathematician?

For centuries, mathematical theories have proven uncannily accurate at describing—and predicting—the physical world. What is it that gives mathematics such power? Mario Livio attempts to answer this question in his new book Is God A Mathematician?. Spanning such fields as cosmology, physics, and cognitive science, Dr. Livio offers an accessible and lively account of the lives and thoughts of some of the greatest mathematicians and scientists in history, from Archimedes to Galileo, Descartes to Gödel, and on up to today. Recorded on January 12, 2009.

Download | RSS | iTunes (1hr 5 mins, 60 MB)

From the Field: Evolution: What the Fossils Say and Why it Matters

Donald R. Prothero vividly illustrates how the fossil record is now one of the strongest lines of evidence for evolution. Tackling subjects ranging from flood geology and rock dating to neo- Darwinism and macroevolution, he takes us on a grand tour that sheds light on such subjects as invertebrate transitions, the reign of the dinosaurs, and the leap from chimpanzee to human. Donald R. Prothero is Professor of Geology at Occidental College and author of the new book Evolution: What Fossils Say and Why it Matters. Recorded on January 8, 2009.

Download | RSS | iTunes (1hr 14mins, 74 MB)

The How and Why of Climate Change and What It Means for the Future

In this talk, Edmond A. Mathez presents the scientific evidence for climate change, describes some of the possible impacts, and explores potential solutions. Dr. Mathez is curator of the exhibition, Climate Change: The Threat to Life and A New Energy Future and author of the new book, Climate Change: The Science of Global Warming and Our Energy Future. Recorded on January 6, 2009.

Download | RSS | iTunes (1hr 10mins, 65 MB)