Some kinds of things, like wings, or eyes, have evolved multiple times in many lineages. Other kinds of things, like human language, have only evolved once. From this, it’s tempting to say that certain kinds of adaptations are more possible than others.
But, what is a possibility, exactly? Commonly, we talk about possibilities as things which might happen, but haven’t yet. Yet it’s a bit misleading to talk about possibilities as “things” because they don’t actually exist in the physical world. Possibilities are just potentials. But still, possibilities have a huge effect on the sorts of living forms that actually do come into physical existence.
In his book Investigations, Stuart Kauffman talks about evolution as a process of exploring the adjacent possible. What this means is that as life evolves, its forms explore the immediate possibilities that are available to them, and transform them into actualities.
Evolution doesn’t proceed in straight lines. Living forms wander around the space of possibilities they were born into, and sometimes multiple lineages will stumble upon the same possibility independently, often from completely different directions.
A great example of this can be seen in the evolution of the columbine flower, from the genus Aquilegia.
The Aquilegia genus evolved in Eurasia, where it was primarily pollinated by bees. But when some members of the group migrated to the Americas, they quickly discovered a new pollination possibility: hummingbirds. Some Aquilegia species changed colors from blue to red and evolved longer nectar spurs to accommodate the hummingbird beaks. Once this hummingbird friendly phenotype had evolved, a new possibility emerged: hawkmoth pollination. Some flower lineages changed again from red to yellow, and evolved even longer nectar spurs.
This hawkmoth pollination syndrome only became a possibility after the hummingbird possibility had been actualized. But this wasn’t a linear sequence, like a row of dominoes. Several lineages independently converged on both the hummingbird and hawkmoth pollination syndromes, while many more lineages never discovered the possibility.
This example isn’t simply a case of convergent evolution. It shows that certain kinds of possibilities emerge over and over during the history of life, but they are only accessible by following particular paths.
For more about the amazing history of Aquilegia evolution, check out this lecture that Molly Edwards of Science IRL gave for the EvoS Seminar Series.
The EvoS Seminar Series (and this article) tries to provide a chain of content between science and narrative. We post articles, live lectures, and explainer videos which all present the same ideas from different perspectives and different levels of complexity.
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