Watch Emma Hammarlund's mini lecture here
Could you describe the journey from forming your contrarian theory, to working with cancer researchers, and finally to what we now know thanks to your research?
Oh, that is a long story! A good microbiologist pointed out to me that geologists are in a particularly tricky field, since it is hard to go back into the lab and test hypotheses.
Around that same time, conflicting observations were being made regarding the “oxygen story” surrounding the Cambrian explosion. That, along with her comment, made me want to go back into the lab and study the formation and diversification of multicellularity – that is – complex life, and therefore, animal life.
I ended up choosing cancer tumours as a model, although I shall admit it is an ugly and incorrect model of multicellularity, but it had to do. It was something I could study in a lab environment.
My first observation was that cancer cells do not care at all about oxygen. It was very humbling to realize that most processes in our body occur in a relatively low oxygen environment. For example, stem cells and tissue renewal may be particularly sensitive to oxygen. This was a new conundrum that I got very interested to explore. I’ve learned and keep learning a tremendous amount from the cancer field.
It is surprising is that we may have been looking for an explanation in the entirely wrong place for decades.
Would you say your findings upend the prevailing theory that the Cambrian explosion was due to an oxygen-rich environment?
Considering the nature of science, I wouldn’t think that idea goes away so easily. Partly because it’s such an engrained hypothesis, that we think we can understand. We have all experienced the importance of oxygen when diving too deep or losing our breath during training.
And we as observers apparently are more attached to rationales that we understand, than those that remain hard to understand. However, there are other lines of evidence also pointing towards a view where other factors than higher oxygen would be the answer. So yes, slowly the field is building on a new mountain of observations and data that may tell a different story.
We, as observers, apparently are more attached to rationales that we understand, than those that remain hard to understand.
What did you find in your latest study?
We found that daily swings of oxygen concentrations, from high in the day to low at night, would likely have prevailed in the environments were early animals would have liked to be, eat and colonize. This means that the daily swings would have exposed early colonizers to physiological stress. And this physiological stress could have worked as a filter or selective pressure to those that could cope with daily oxygen fluctuations.
We also found that mechanisms to cope with oxygen fluctuations has a cost, but that this cost is worth it if the fluctuations are regular. In regularly fluctuating conditions, animals with costly but more potent mechanisms to cope with this stress would be ‘winners’.
Most other biological revolutions are thought to be triggered by a crisis. For example, the extinction of dinosaurs gave rise to mammals. It was a phase of destruction and creativity.
Was this surprising?
Good question. I would say that that three things were suprising:
It is surprising is that we may have been looking for an explanation in the entirely wrong place for decades. We’ve been searching for changes in the atmosphere, where we know changes are slow and stretch over millions of years. It’s hard for selection and ecology to work on such time scales. Down at the sandy warm seabed, however, our models show that daily swings would be so severe that animals would have had to adapt to it.
At the same time, we have previously ignored what may have happened on a daily basis in Earth’s history. It’s hard to track, but with computer models it is possible.
Finally, we’ve been thinking that oxygen was ‘good’ and triggered the Cambrian explosion. This despite the fact that most other biological revolutions are thought to be triggered by a crisis. For example - the extinction of dinosaurs gave rise to mammals. It was a phase of destruction and creativity. Interestingly, our work now also invokes environmental stress for the Cambrian explosion. When you think about it, it does make some sense!