After Darwin at AMNH: Rob DeSalle

Monday, December 14 10:19 am

Curator Rob DeSalle Explains the Limitations of Genetic Ancestry Tests

This year, scientists at the American Museum of Natural History are celebrating 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.

An annotated academic poster from a conference held at AMNH in 1932 shows the inheritance of two genetic sequences commonly used in ancestry testing. On top of Charles Darwin’s pedigree, DeSalle plotted mitochondrial DNA in red and Y-chromosome in blue. Darwin is outlined by a blue square. - AMNH

When Henry Louis Gates Jr., Harvard University professor and host of the PBS series African American Lives, learned that his Y-chromosome—a gene popularly used to trace male ancestry—“goes back to Europe,” he joked that he was having an identity crisis. And in his best-selling book The Seven Daughters of Eve geneticist Brian Sykes suggests that 95% of all Europeans are descended from just seven Stone Age women. He used mitochondrial DNA, inherited directly from mothers and employed by companies for ancestry testing of the maternal ancestry, for this work.

These are dramatic moments, but they are based in part on misleading assumptions, according to geneticists like Rob DeSalle, Curator in the Sackler Institute for Comparative Genomics at the Museum. “Ancestry testing is pushed as simple and straight-forward,” he says. “But it is not. Often the verbal history passed down in families is more accurate than ancestry DNA testing done now.”

DeSalle, along with Museum colleague Ian Tattersall, turned to the family history of the most famous of evolutionary thinkers to illustrate their point. By simply mapping basic inheritance onto Charles Darwin’s pedigree, it is easy to see how quickly a specific Y-chromosome or sequence of mitochondrial DNA (mtDNA) can be lost in a lineage. Darwin’s Y-chromosome, for example, is probably found in only two of his living descendents. Only three of his four sons reproduced and one of these sons only had daughters. Ultimately, the number of male descendents of Darwin’s two sons who had male offspring dwindled to a very small number. There are many direct male descendents of Charles Darwin living today, but most of them do not have his Y chromosome. Read more »

After Darwin at AMNH: John Flynn

Friday, November 20 3:51 pm

Fossil Hunting Among Volcanoes With Paleontologist John Flynn

This year, scientists at the American Museum of Natural History are celebrating 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.

It was during a siesta in the woods that Charles Darwin, exploring the Chilean coast more than three years into his voyage on the H.M.S. Beagle, was shaken by one of the strongest earthquakes known to the local inhabitants. On that February day in 1835, Darwin not only witnessed “the most awful spectacle I ever beheld… [with] not one house left habitable,” as he wrote to his sister Caroline, but he also had an epiphany:

The most remarkable effect of this earthquake was the permanent elevation of the land… [which revealed] mussel-shells still adhering to the rocks, ten feet above high-water mark.… At Valparaiso… similar shells are found at the height of 1,300 feet: it is hardly possible to doubt that this great elevation has been effected by successive small uprisings.

Chilecebus, a reconstruction of which is shown above, is one of the fossils that John Flynn and colleagues have uncovered in the Chilean Andes (Illustration by Velizar Simeonovski, courtesy of John J. Flynn)

While sailing across the Atlantic and past Tierra del Fuego, Darwin had been reading Charles Lyell’s Principles of Geology, in which Lyell laid out the case that massive geological change is based on the slow accumulation of minute changes over time. It was through this lens that Darwin observed the volatile, shifting landscapes that partly informed his theory of evolution.

We now know that the active geology of Chile—the earthquakes, volcanoes, and formation of the Andes Mountains themselves—is caused by the squeezing of the Pacific Ocean plate under South America and back into the Earth’s interior. Paleontologist John Flynn and colleagues André Wyss, Reynaldo Charrier, and Darin Croft have traversed this geology over the last 20 years to learn more about both the history of the Andes and the unusual extinct fauna that lived on this former island continent. Mountain uplift drives fossil beds to the surface, weathering exposes fossil teeth and bone, and volcanic debris dates their time frames.

“We were first drawn to Chile because amateur naturalists found whale bones at 6,000 feet in the 1980s,” says Flynn. “Since then, we’ve uncovered a remarkable mammalian menagerie that explains some of the diversity seen today and also helps us understand more of the uplift history of this 5,000-mile-long mountain chain that forms a spine along then entire western edge of South America.” Read more »

After Darwin at AMNH: Mark Siddall

Wednesday, November 04 4:43 pm

De-Leeching Ankles on a Desolate Coast with Mark Siddall, Curator of Invertebrate Zoology

This year, scientists at the American Museum of Natural History are celebrating 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.

The Island of Chiloé may protect part of the Chilean coast from the winds of the Pacific Ocean, but it offers little refuge for the travelling naturalist.

Americobdella valdiviana exposed by turning over a rock - © M. Siddall

When Charles Darwin rode with his team across the island on January 22, 1835 he recalled a beautiful day and “trees…in full flower [that] perfumed the air.” Yet even this lovely vista “could hardly dissipate the effects of the gloomy dampness of the forest. Moreover, the many dead trunks that stand like skeletons never fail to give to these primeval woods a character of solemnity.”

More than 160 years later, Mark Siddall and his graduate student Liz Borda made a similar excursion to what is now the Parque Nacional de Chiloé. As they tramped through dense stands of old-growth Nothofagus and Fitzroya trees in intense wind and

driving rain, they found they shared Darwin’s observation that if they “could forget the gloom and ceaseless rain of winter, Chiloé might pass for a charming island.”

The project that brought Siddall and Borda to Chile shared something else with Darwin, too. “Our purpose in Southern Chile was to rediscover two species of leeches, Americobdella valdiviana and Mesobdella gemmata, that I thought were critical to understanding the evolution of this group,” says Siddall. “Transitional forms—species that have characteristics of two distinct but evolutionarily related groups—are central to Darwin’s theories.”

Read more »