Guy Robinson, Ecological Sleuth
The mammoth, mastodon, glyptodont, stout legged-llama, giant ground sloth, and sabertooth cat are not your average pack of murder victims, yet some scientists have long suspected that they succumbed to foul play. These species were among the megafauna who once roamed the landmass of North America, disappearing at the end of the Pleistocene, some ten to eleven-thousand years ago.
If science is a kind of detective work, then GSAS biology doctoral graduate Guy Robinson has earned his Holmes hat as a kind of ecological sleuth. After all, it’s not many a Sherlock who can read clues from North America’s late Pleistocene period, to discover a villain in the case of approximately 35 genera of vanished megafauna, the large vertebrate mammals who once roamed the continent freely in the era before our most recent ice age.
Their extinction was total enough to raise suspicions among the 19th and mid-20th century archeologists and paleontologists who studied their remains. Was it human overkill, or the result of a dramatic natural change in weather and climactic conditions that caused the massive extinctions of a whole spectrum of burly beasts? Environmental change or aggressive overkill, or perhaps some combination — which was really responsible for the large-scale disappearance of so many species?
The remoteness of the time period in question added to the ambiguities. Even with the help of radiocarbon dating, it was quite difficult for scientists to pinpoint any sequence to events occurring more than ten thousand years before. According to Robinson, the thesis that human civilizations did away with the megafauna was first discussed in the 19th century, but it hadn’t become a formal hypothesis until 40 or 50 years ago. “A chap at the University of Arizona suggested that perhaps humans were responsible for extinctions 10,000 years ago. He laid this out in quite testable form and it’s been debated ever since.”
Paul S. Martin’s 1967 “blitzkrieg” hypothesis has occasioned debate ever since it proposed that the first human beings who crossed the Bering Strait caused the rapid demise of the megafauna. Others argued that it was the end of the most recent North American ice age, when rapid fluctuations in the climate dealt the fatal blow by cutting off the megafauna’s food supply.
“Science is detective work,” Robinson says. “It was pretty challenging, but the idea of being able to find out what happened on a quite contentious question appealed to me.” Robinson’s findings of late have earned him recognition among his fellow scientists and the general press: his work has been written up recently in Science magazine, as well as earning mention in the Boston Globe and the Dallas Morning News. The scientific community is once again buzzing with debate about the overkill hypothesis, a familiar flint for discussion that recently ignited new sparks.
As a student in the GSAS biology program, Robinson had worked with Fordham paleoecologist David Burney in his lab. He plugged in some of the same methods his mentor had used in Madagascar, selecting four sites right in New York State. Robinson notes: “New York has tremendous potential. This region was under ice, but close to its Southernmost limits” Robinson found physical conditions favorable to testing the Martin overkill hypothesis. Digging below the water table, “we had to pump the water out to get a sample of the mud. We sometimes drove a sediment coring device and went down quite deep.”
The soil in many places held just the right neutral PH value to preserve an entire sequence of spores, pollen, and charcoal bits within the fine sediments — allowing Robinson to trace datable clues on the microscopic level. He searched beneath the lakes, bogs and watering holes where megafauna once bathed. The answers he found were written in the earth.
“I don’t deal with direct evidence,” the fossilized or otherwise preserved bones of individual creatures, often found unearthed within cave-beds, “but with proxy evidence. If you find a kill site, it just tells you that this particular animal was killed, but that doesn’t necessarily lead to extinction. Indirect evidence can show a profound change in the population.”
Choosing his sites carefully, Robinson was able to pump and excavate layers of alluvial mud and examine concentrations of fungal spores called “Sporormiella” from the dung of the megafauna. He compared these chronologically with the tiny carbon traces left behind from frequent landscape-level fires (signs of encroaching human activity), thus yielding a time frame of human settlement. A tree pollen analysis helped to determine the dates of large-scale climactic changes. His conclusion: human beings were on the move in the continent about 1,000 years before the most dramatic climate swings.
“In North America,” Robinson notes, “it was probably a combination of the hunting and landscape-level transformation” that did in the megafauna. “But it’s probably not for millennia that we see real agricultural alterations. I think it’s hard to accept that people of Paleolithic times — old stone age people, without metal tools — could have instigated an ecological crisis. It’s a lesson for where we stand now. Although eco-systems can be quite resilient, once they’re put into a state of collapse it’s hard to resist that direction.
“Humans may have showed up [in North America ] at a period of natural vulnerability. But we’ve gone from glacial to interglacial conditions at least 17 times in the last 2 million years. Yet it’s only the last time, when humans showed up, that we lost over 75 percent of our large animal populations. We’re left with one-quarter of what we had. The bison, elk and moose were left. We lost the mammoth, mastodon and wild horse. The horse was a member of the megafauna, and was only reintroduced after Columbus.”
Only under certain soil conditions can one still find the spores and pollen intact from 10,000 years before.
“Pollen analysis is a powerful tool. The factors common in sites in our area offered the right conditions.” These conditions included sediments located below the water-table, and an anoxic environment that virtually prevents the bacterial degradation that would naturally occur if oxygen was available. “A neutral PH preserves a whole sequence of sedimentary spores, pollen and charcoal. And fine sediments are very good. You can read the sequence of sediments from bottom to top,” almost like the pages of an earthen book; the story of North American, written in letters of sediment. “Sometimes pages are missing.”
Robinson feels that studying the ecological catastrophes of long ago can give us meaningful insights into our world now, and the wanton destruction of living species in the still-wild corners of our globe.
Robinson at Fordham
Guy Robinson first came to study at Fordham as an evening student in the Fordham College of Liberal Studies. At that point his school was still known as Ignatius College. He received his bachelor’s degree in biology in 1997. An adult student, originally from England and more recently a resident of Los Angeles, Robinson had worked for some ten years as a carpenter before returning to school.
His undergraduate work at Fordham, while meaningful to him, gave him few clues about where his doctoral research might take him. “I did the standard set of intro courses in biology.”
Robinson chose to do his graduate work at Fordham’s Graduate School of Arts and Sciences, entering the doctoral program at age 42. Once in the program, he discovered Dr. Burney’s lab and became intrigued by the kind of investigations being done.
“Once I decided on ecology, I had to decide what my particular focus would be.” He liked the time and space for exploration that the program afforded. “I settled on a research topic after two years in the program. I appreciated the flexibility. For me, it was an advantage that I could come in without making up my mind. Most other programs expected you to know what you wanted from the outset.”
As a teenager, Robinson had spent time at archeological sites and learned the methodology and care that went into executing a successful dig. Meeting Dr. Burney and studying paleoecology in his classes, Robinson says, “opened up another world. What really grabbed me was looking at deep time. I’d always wanted to do geology and having somebody just lay it all out, even as a sketch, really struck my imagination.
“It’s very humbling in a way. You realize how insignificant your own lifetime is when you think about such long time periods.”