When considering the impacts humans have on the environment, Andrew Whitehead likes to think about the photography of Edward Burtynsky. 

As he stood in front of the crowd gathered for the April Davis Science Café at G Street Wunderbar, Whithead toggled through Burtynsky’s photographs that showed overhead views of the Earth as a space indelibly marked by human hands. Areas mined for minerals in the expanses of Australia, aquaculture facilities off the coast of China, spaces reserved for dryland farming in Spain and even the arterial highways winding through Los Angeles.  

“What I’m trying to communicate with Edward Burtynsky’s photography is just the scale of landscape transformation by human activities in lots of different parts of the globe by lots of different kinds of activities,” said Whitehead, a UC Davis professor of environmental toxicology and chair of the department. 

“But we are also reciprocally shaped by the environment and sometimes that’s a cycle,” he added. “The changes that we impose on the environment come back to affect our own health and wellbeing and our own evolutionary path as a species.” 

Whitehead’s Davis Science Café, an event hosted by Jared Shaw and the Department of Chemistry, explored not only how our actions as a species affect ourselves, but also how they impact the innumerable species we share the Earth with.   

Defining evolution in the Anthropocene 

What is evolution? 

If you ask Whitehead, he’ll tell you that his favorite definition, one that is formula-like in its simplicity, is “Change over time by descent with modification.” 

“I like this definition because almost every word has a really important component to the meaning,” he said. “Life is not static because environmental change is the norm” and “evolution is a process that unfolds across generations.”

But those generation times aren’t temporally equivalent across species. A virus with its short generation time, for example, evolves much more quickly than the much longer-lived elephant.

However, the environmental changes affecting both species, and all the rest covering the globe, are similar. 

With our current epoch being colloquially called the Anthropocene, those environmental changes are, and have been since the Neolithic, increasingly shaped by humans, Whitehead said. We’ve domesticated plant species for agriculture, shaped dog breeds for companionship and, in our more recent past, instigated pesticide resistance in insect species, among other manipulations both intended and unintended.

“We’ve gone from societies of hunter-gatherers that tended to be population sizes of many hundreds to low thousands” to now when “many parts of the globe where humans are living in high density is hundreds of thousands to millions and should-to-shoulder,” Whitehead said.

And our species’ proliferation in both size and density has consequences for the environment.   

Some species thrive, others struggle

In our urbanized environments, some species thrive while others struggle. Coyotes, crows and raccoons are just some of the animals that seem to make do in our cityscapes. But the behavioral adaptations and genetic diversity underlying their urban success is not the norm.  

“There are lots of species that can’t evolve to this change in the environment and are being excluded from altered environments or are driven to extinction,” Whitehead said. 

In his research, Whitehead is trying to figure out what makes the thrivers thrive. 

“These kinds of creatures that…tend to be evolutionary winners, they can evolve very, very quickly because they’ve got massive population sizes, meaning that they have massive genetic gas tanks,” Whitehead said. “Genetic variation is the fuel for evolutionary change.”  

To understand this better, Whitehead conducts research on killifish, a genus of fish that can be found in both pristine and urbanized coastal environments across North America. 

A fisheye’s view of evolution

Whitehead and his colleagues have found that killifish populations living in urbanized environments have evolved a pollution resistance that their counterparts living in pristine environments haven’t.  

“These are really, really polluted urban estuaries where you can find killifish populations that appear to be normal and healthy,” Whitehead said. “When you measure the amount of chemical there, these are lethal environments and there shouldn’t be killifish there.”  

In their work, the researchers have created a database to identify the genetic pathways different killifish populations used to evolve this pollution resistance. How are the similar? How are they different?   

“So why did killifish come up with this solution whereas other vertebrates don’t?” Whitehead said. “We tend to think of fish, such as killifish, as the kind of creatures that relatively small population sizes, and long generation times.”

But killifish have insect-like levels of genetic diversity, according to Whitehead.  

“Killifish tip the scales,” he said. “So is the solution [to pollution] evolution? It has been for killifish.”   

“But this is the exception, not the rule,” he added. “Evolution tends to be the rule for species that we seek to destroy [such as pests and insects]; whereas extinction is the rule for species that we want to preserve, which tend to be vertebrates.” 

Unlike killifish, humans and many other vertebrate species tend to have lower levels of genetic diversity, meaning that we’re more susceptible to negative environmental change. 

“Fortunately, we’ve got cleverness and technology to solve some of the environmental problems that we cause for ourselves and other creatures,” Whitehead said. “Whether we’re thinking about medicine, or we’re thinking about agriculture, or thinking about problems that come from habitat continuity, evolutionary thinking is leading to new ways to solve these problems.”   

The Davis Science Café is held every second Wednesday of the month. Learn more about the Davis Science Café. 

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