Extinctions: Interview with Andrew Knoll Part II

An Interview with Andy Knoll

Part II: The Role of Extinction in Evolution




Why aren’t extinction events/evolutionary perturbations seen as progressive changes?

“I don’t think over the next hundred years we’re going to have the kind of effect on this planet that a meteorite hitting 65 million years ago did.” -Andy Knoll
Image Credit: NASA

I think if we look at the history of the planet, perturbation certainly has had short-term bad consequences for diversity. This perturbation causes clusters of extinction to occur in short periods of time. But, by removing the organisms that dominated the landscapes before the perturbation, you open up the possibility that the survivors will have new sets of characteristics that weren’t there before. So in that sense, perturbation is a driving force in evolutionary history. I would say that on the time scale of our planets’ history, physical perturbation has played just as important an evolutionary role as genetics has. So, the central fact of our planet, as far as biology is concerned, is that it’s dynamic and always changing and biology changes in concert with that. Whether that leads to progress…

Progress is a very loaded term for people who study the philosophy of biology. It certainly leads to change, and there have been long-term changes that have a directional arrow associated with them. Whether or not that’s progress or just change I think depends on the philosophy of the individual.

Are we on the verge of a major extinction event?

No, I don’t think we’re on the verge of a mass extinction. People talk about the sixth great extinction – there have been about five moments in the history of this planet where as much as ninety percent of the diversity has disappeared in a very short time period. Those have been evolutionary turning points in the history of animals and plants. But I don’t think over the next hundred years we’re going to have the kind of effect on this planet that a meteorite hitting 65 million years ago did.

Andy Knoll and Norman Myers (above) agree that we should not compare today’s extinctions to those that occurred in the past.
Image Credit: Jane Scherr

On the other hand, there have been many more intervals in the history of our planet where a smaller percentage of the biota has changed, where ten or twenty percent of the species disappeared. That’s certainly possible, and for certain groups of organisms like birds, large mammals, and certain types of plants, there could be extinctions that will make the future a very different place from the past. When we talk about what’s happening now, I don’t think we want to suggest that we’re going the way of a Cretaceous mass extinction. That’s not to minimize what we are doing. If the next hundred years plays out the way it might, the changes that we visit on the planet would certainly be visible to a geologist looking back 100 million years from now.

In terms of recovery, what are the lessons we can learn from past extinction events?

We do have some historical record of how the biota recovers after mass extinctions. There’s good news and bad news. The good news is that in the aftermath of every major extinction in the past, biology has recovered. There have been survivors and they have expanded and diversified to essentially rebuild ecosystems.

There’s two kinds of bad news. The first bad news is that the timescale of recovery takes millions of years. So, you might gain comfort by saying ‘well, you know, if we lose all the big animals in Africa, they’ll come back.’ They might, but they won’t come back on the timescale that would be remotely imaginable by any historical scale that we know. Your great great great great great great grandchildren won’t witness that recovery – it’ll be long after they’re dead.

The other bad news that Norman Myers and I talk about in our paper has been addressed less well than it should be, which is: there’s no reason to believe that past extinctions are the right scenario for thinking about today’s extinctions. When the meteorite hit the Earth 65 million years ago and killed the dinosaurs and less evocative creatures, there was a short-term perturbation. Immediately after that, or very soon after that, the environment started to heal. That is, the perturbation went away, some sort of physical normalcy was restored to the planet, and then biology rediversified. That’s been true of most of the mass extinctions: the perturbation was short and recovery began soon after. But in the present case, the perturbation is us. The perturbation arrives and then it stays. So, I’m not sure how closely we can take the lessons from the past and use them to predict the future. In terms of any human future that we can envision, we don’t have a perturbation that goes away, but instead we change the nature of the world we’re living in. Then only through some sort of active management program can we retain or rebuild biological diversity, or learn to live without it.

Related Web Pages

Biodiversity interview with Andrew Knoll, professor of evolutionary biology at Harvard University (original video)

Astrobiology at Harvard:




Genetic engineering:


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