Students, staff and other guests attended a lecture by David Jablonski titled “Mass Extinctions and Evolution: What We’ve Learned Since Darwin,” on Feb. 12, Darwin Day.

The lecture in the Earth and Space Sciences building encompassed the goals of the celebration of Charles Darwin’s birthday: to improve scientific literacy and to diminish scientific denialism.

Jablonski, a professor in the Department of the Geophysical Sciences and the Committee on Evolutionary Biology at the University of Chicago, spoke about the importance of understanding evolutionary trends and their application to our modern world.

Using a editorial cartoon from The New York Times that depicted dinosaurs dressed in modern attire with humans as their pets, Jablonski pointed out that land-based fossil records, like those of the dinosaurs, do not help to prove or disprove claims surrounding evolution.

The cartoon raises questions about the driving forces of evolution and why some species survive while others do not. In order to answer these questions, Jablonski said that we need richer fossil records like those of marine bivalves, such as scallops, mussels and oysters, since the creatures are more abundant
and diverse.

“They are actually the perfect evolutionary laboratory for studying the big picture of extinction, unlike the dinosaurs,” Jablonski said.

Marine bivalves have approximately 3,000 genera, or groups of species, which have diverse life habits and survive all depths and latitudes. Jablonski noted that we may have picked up some of these fossils on the beach.

On the other hand, dinosaurs were confined to the area where they were found and have many gaps in their evolutionary lineage, so it is difficult to study the conditions surrounding their existence and eventual extinction.

In order to understand why certain species survived mass extinction, such as the extinction at the end of the Cretaceous period which occurred 65 million years ago, Jablonski studied fossil records of marine bivalves from before and after that mass extinction from a meteor strike.

He noted that before the threat of mass extinction, species with widespread ranges had a greater chance of survival from smaller threats, like a typhoon.

However, Jablonski said that the exquisite adaptation in the hinge structure of reef-like bivalves was lost. Survival was narrowed down to specific properties in a species.

“It happened to be linked to a property, not a geographic range that set them up for extinction when the rock fell out of the sky, and the rules for survival changed,” he said.

Furthermore, he noted that not all survivors of mass extinctions are winners. Some species that survive remain confined to a specific area.

There are a few species that survived the mass extinction at the end of the Cretaceous period, but are confined to the deep sea area in the Indian Ocean. They are at risk of dying out. He termed those species “dead clade walking.”

For today’s world, Jablonski said that although the world is not yet close to another mass extinction, there are pressures on biota. Many species are being affected by high carbon dioxide levels in our oceans and are experiencing a domino effect.

Jablonski said that humans have a moral and scientific obligation to save species that have limited ranges.