ENST: Trapdoors in the Fitness Landscape

A commonly-used metaphor for
Darwinian fitness collapses
into a flat field of sinkholes

Holey landscape! Here goes another Darwinian assumption, falling into a trapdoor and out of sight.

Trapdoors in the Fitness Landscape
Scientists Revive Worries About an Evolutionary Metaphor
by David Coppedge
Evolution News & Science Today, January 4, 2024

Sewall Wright concocted one of those metaphors in science that lingers long past its “best by” date. In 1932, he coined the term “the fitness landscape.” He envisioned a mythical land of peaks and valleys, with the peaks indicating higher fitness, and valleys populated by evolving organisms starting out on their journeys toward progressively higher fitness levels. Impelled by the struggle for existence, organisms would climb higher till reaching a peak. One difficulty with this picture appeared soon after the metaphor gained popularity: to get to a higher peak, an organism would have to climb down, lowering its fitness on the way to a neighboring peak. Some workarounds were concocted, but the evocative metaphor lent itself to 3-D graphs and formulas of positive selection, giving evolutionary biologists hopes of empirical rigor as they measured their research organism’s progress up the landscape.

Illustration of a staircase to the summit of Mt. Improbable, supposedly allowing an organism to reach a steep fitness summit by slow and gradual steps. (Credit: Illustra Media, Darwin’s Dilemma.)

Stability of the Landscape

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Unwarranted assumptions are the bugaboo of clever models like this. One is the stability of the landscape. Does the hypothetical landscape undulate over time, such that a peak at one epoch becomes a valley in another? After all, the dynamic environment is oblivious to the needs of organisms. How quickly does a given habitat change? How can evolutionists be sure that fitness for a savannah does not become a detriment if the population finds itself in a habitat undergoing desertification? For reasons like this, Mustonen and Lässig in 2009 dubbed it a fitness “seascape” instead of a landscape.

Another of Wright’s assumptions was that the fitness landscape follows Gaussian curves consisting of smooth lines without discontinuities. Even if some of those Gaussian curves rose steeply like a cliff, Darwin defenders like Richard Dawkins could get their organisms up to the summit of Mount Improbable by envisioning a gradual staircase from another direction, allowing natural selection to maintain Darwin’s narrative of the accumulation of small, incremental steps.

But what if the Gaussian assumption is wrong? What if, instead, the structure of the landscape is like a block of Swiss cheese, flat and riddled with holes that a blind watchmaker cannot foresee?….

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Darwin falls through a trapdoor in his fitness landscape.