Birds. Brains. Yeast. Spiders. Societal culture. This medley of topics seems unrelated at first glance. But the research of biologist Carlos Botero inspects each of these subjects and more in his quest to study the ecological and evolutionary causes of fluctuating selection.
The premise of fluctuating selection is that the pressures shaping an organism’s evolution oscillate, not just on glacial timescales but also seasonally. Because of such variation, organisms must choose what ecological strategies to pursue in order to maximize their chances at reproduction. When no information is available, organisms must bet on their survival by choosing between two strategies. Some organisms may choose a conservative approach that minimizes costs. In contrast, others diversify their behavior by “putting their eggs into more than one basket” in hopes of some offspring surviving.
Some organisms literally put their eggs in more than one basket. Botero recently found that this is true for avian “brood parasites” (that is, birds that lay their eggs in other species’ nests rather than expend the resources to raise their own young). In August 2020, he co-authored an article titled Ecological uncertainty favours the diversification of host use in avian brood parasites. In this article, he describes that brood parasites that occupy highly uncertain environments tend to diversify by laying their eggs in the nests of more and more distantly related species of birds. Such active diversification helps spread the risk of failure by accessing hosts with different behaviors and ecological niches.
It may seem curious to humans how host species often do not recognize that one of their children looks totally different. But this perspective is heavily biased toward large brains, which are not always advantageous. Botero also researches the tradeoffs of more complex and capable brains. While large brains allow an organism to flexibly plan and innovate in the presence of severe environmental pressures, small brains enable an organism to devote its resources toward stronger bodies, robust digestive tracts, greater defense, and potentially more reproductive output. The tradeoff, of course, is intelligence. Host birds may not even be able to distinguish between their own children and the vicious parasitic birds that they are feeding.
Why birds? Botero reflects that “they’re cool, and they’re everywhere.” He comes from Colombia, the country with the greatest number of bird species. He’s spent much of his time in the wild just watching them, appreciating their beautiful songs, intricate feathers, eccentric behaviors, and enthralling evolutionary histories.
But Botero does not only study avian evolution. He also investigates the evolution of human behavior and culture, applying his same basic biological questions about environmental pressures to an entirely different species—Homo sapiens—with uniquely complex societal orders and cognitive abilities. One of Botero’s fascinating finds in this field is the correlation between ecological uncertainty and beliefs in moralizing high gods. Specifically, he and his team found that in societies that live in harsher and less predictable habitats, people are more likely to report beliefs in deities that punish behaviors that contradict social expectations (“amoral” behaviors). His study linked these beliefs with the ecological advantages of cooperation, a pattern that has also been reported in birds (as seen in his 2017 paper).
As the climate crisis intensifies, it is critical to understand how life, including humans, adapts to the increasing variability and intensity of environmental pressures. Researchers like Botero are leading this charge, providing a perspective from evolutionary biology that may help us address some of the most pressing environmental issues of the Anthropocene.
Antonson, N.D., Rubenstein, D.R., Hauber, M.E. et al. Ecological uncertainty favours the diversification of host use in avian brood parasites. Nat Commun 11, 4185 (2020). https://doi.org/10.1038/s41467-020-18038-y
Fristoe T, Iwaniuk A, & CA Botero. 2017. Big brains stabilize population dynamics and facilitate colonization of variable habitats in birds. Nature Ecology & Evolution doi: 10.1038/s41559-017-0316-2.
Botero CA, FJ Weissing, J Wright, and DR Rubenstein. 2015. Evolutionary tipping points in the capacity to adapt to environmental change. Proceedings of the National Academy of Sciences, USA. 112(1): 184-189. doi: 10.1073/pnas.140858911
Griesser M, Drobniak SM, Nakagawa S, Botero CA (2017) Family living sets the stage for cooperative breeding and ecological resilience in birds. PLoS Biol 15(6): e2000483. https://doi.org/10.1371/journal.pbio.2000483
Carlos A. Botero, Beth Gardner, Kathryn R. Kirby, Joseph Bulbulia, Michael C. Gavin, Russell D. Gray. The ecology of religious beliefs. Proceedings of the National Academy of Sciences Nov 2014, 111 (47) 16784-16789; DOI: 10.1073/pnas.1408701111