After Darwin at AMNH: David Hurst Thomas
Thursday, January 28 4:29 pm
Curator David Hurst Thomas Tests Darwin in Archaeological Sites
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.
Part of the St. Catherines archaeology team shucking oysters to determine the amount of energy (in calories) that people can retrieve in relation to the amount of energy spent collecting and processing. Credit: Lorann S.A. Pendleton.
Deer, clams, oysters, alligators: if you walked the length of St. Catherines Island off of Georgia, what would you pop into your mouth? David Hurst Thomas, curator in the Division of Anthropology at the Museum, uses optimal foraging theory to interpret the remains of thousands of meals left behind in archaeological sites across the island.
Optimal foraging theory puts an evolutionary spin on what people chose to eat. The assumption that individuals decide what to consume in a way that maximizes the total energy return and minimizes the energy they must spend to search for, collect, and prepare food items in their environment. This approach is known as the “diet breadth model,” a series of testable hypotheses about what an efficient forager will pick (and not pick) from the array of available food.
“Darwinian evolutionary ecology allows us to frame some concrete expectations about what a forager should choose to gather,” says Thomas. “Suppose someone dropped a pot of coins. Some would be selective, picking up only silver dollars, and others would rush to pick up everything. The diet breadth model allows us to distinguish between these strategies in archaeological sites.”
Thomas and his team have spent more than 30 years excavating different archaeological sites throughout the island’s 14,000-plus acres. Recently, the team conducted a series of foraging experiments that, as Thomas puts it, “hook theory to dirt archaeology” by mapping the most efficient strategies for harvesting the available foodstuffs. They harvested oysters, dug up clams, butchered diamondback terrapins, and drank periwinkle soup. For each food type, the archaeologists recorded the length of time and amount of energy expended for collecting and processing. These data were then compared to the amount of available energy gained from food to answer a key question: if I invest one hour in foraging, what is the energetic return on that investment? The result, expressed as kilocalories per hour, allows researchers to compare different food types.
The experiments showed that one of the highest-ranking food items on the island was white-tailed deer. If a forager spends an hour finding, pursuing, butchering, and cooking a deer, the return rate would be about 12,000 to 20,000 kilocalories per hour. This means that deer are akin to the silver dollar in a pile of change. Archaeological sites throughout the island confirm venison’s importance in the aboriginal diet since thousands of deer bones have been found. The American alligator likewise has an extremely high energetic return. Experiments conducted in commercial alligator farms in Florida demonstrate an energetic return of about 22,000 kilocalories per hour. But alligator bones are rare in the archaeological sites, suggesting that perhaps alligators were rarer before European contact or that, in this case, the experimental data or the optimal foraging model does not hold.
The rate of return plummets, though, when people dig in the marshes for animal protein. The common eastern oyster (Crassostrea virginica) provides only about 1,000 to 1,700 kilocalories per hour, and tiny marsh periwinkles (Littorina irrorata) are hardly worth the effort to harvest and prepare with a return of between 26 and 135 kilocalories per hour. But archaeological sites show that both resources were consumed in huge quantities, denoting the shifts in diet breadth through time and underscoring the point that efficient foragers can and do change their strategies to fit the circumstances at hand. For example, as population increases, high-ranking food items like deer will likely be overhunted and perhaps driven to extinction. It also might be that different age groups and genders use different foraging strategies.
“The Darwinian paradigm is like an atlas, showing the various roads available for somebody setting out on a driving trip. But the driver gets to choose whether the trip should be quick, scenic, or traffic-free,” says Thomas. “Archaeologists use human behavioral ecology to map the options and understand the fitness benefits, making sense of the ancient stuff we find.”
For additional information, please see “Native American Landscapes of St. Catherines Island, Georgia” (Anthropological Papers of the American Museum of Natural History, 2008).
 Elliot Blair excavating at the Mission Pueblo on St. Catherines Island in 2005. Credit: Anna Semon. |
 Dr. Jason Sherman and Molly Trauten digging test pits in North Pasture, St. Catherines Island in 2005. Credit Anna Semon. |
When the HMS Beagle sailed from England just after Christmas of 1831, Darwin was on board as the ship’s naturalist and geologist. Over the next five years, he made scientific observations and collections in Cape Verde, tropical Brazil, Tierra del Fuego, the pampas of Argentina, Andean Chile, marsupial-dominated Australia, Mauritius, the tip of Africa, and, of course, the Galápagos Islands that so influenced his thinking about evolution.
Darwin’s observations on this voyage must have been central in his thoughts as he walked the sand path around a thicket in Kent, where he spent the next decades crafting On the Origin of Species by Means of Natural Selection, the foundation of evolutionary biology.
The After Darwin at AMNH series explores links between the scientific research work being done at AMNH today and Darwin’s influential work.
Charles Darwin’s route aboard the HMS Beagle from 1831 to 1836. AMNH/David Rumsey Map Collection (www.davidrumsey.com)
