GoKawiilElla Watkins-Dulaney for Asimov Press.
By Ulkar Aghayeva
From the late 1980s through the early 2000s, a famous debate played out between the evolutionary biologists Stephen Jay Gould and Simon Conway Morris on the nature of the evolutionary process.
Gould viewed evolution as radically contingent: if “the tape of life” were to be rerun, he argued, even small environmental changes would result in widely divergent outcomes. The likelihood that any major biological innovation, such as multicellularity, photosynthesis, or intelligent life, could evolve again would be vanishingly small, since each of these innovations depended on a combination of rare events. The crux of Gould’s idea was that “no important and sufficiently specific evolutionary outcomes are robustly replicable.”
Conway Morris agreed that historical contingencies are pervasive in evolution; however, in his view:
…contingency is inevitable, but unremarkable. It need not provoke discussion, because it matters not. There are not an unlimited number of ways of doing something. For all its exuberance, the forms of life are restricted and channeled.
In other words, if we imagine life forms having emerged as solutions to problems in a global search space, there are only a limited number of good solutions given existing environmental constraints. Biology is beholden to the laws of physics and chemistry, which limit which solutions are feasible, let alone optimal.
This is why, as species evolve under similar selective pressures toward greater fitness, they acquire similar characteristics. Indeed, even though evolution is contingent at a local level (such as a specific protein sequence or the shape of a flower), it is remarkably predictable at a global level (such as the very existence of proteins and flowers across many species).
Convergent evolution reflects, then, a widespread predictability of life’s design solutions. Similar biological forms and functions often emerge independently in unrelated lineages. For example, ice growth-inhibiting antifreeze proteins evolved independently in Arctic and Antarctic fishes. Although arising at opposite ends of the globe, these proteins converged at both the sequence and structural level: at both locations, they contain a repeating tripeptide motif of glycine–alanine (or proline)–threonine, with the last amino acid fused to a sugar. The severe constraint of survival in freezing seawater pushed these phylogenetically distant fishes to evolve similar molecular solutions.
Similarly, C4 photosynthesis has been documented in more than 60 different plant lineages, including maize, sugarcane, and papyrus. This convergent evolution involves not just a single protein, but a complex mixture of biochemical and structural adaptations that together enable a more efficient use of carbon dioxide.
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