The Elements of Evolution (42-10) Evolvability

Evolvability

Evolvable organisms naturally separate themselves from less evolvable organisms simply by becoming increasingly diverse. Evolvable species accumulate over time. Evolvability is inevitable. ~ American computer scientist Kenneth Stanley

Evolution often involves augmenting the capacity to evolve by creating variation genes which may become useful later. Evolvability is especially critical to pathogens in their race to stay one step ahead of their hosts: by having a ready reserve of possibilities to apply depending upon what barrier to entry is encountered.

The bacterium Borrelia burgdorferi – using ticks as transport – causes Lyme disease in mammals. The Lyme bacterium has a single protein essential to establishing a long-term infection. B. burgdorferi keeps in its genome – left unexpressed unless needed – an assortment of genes to alter the expressed protein to overcome a host’s immune defenses.

Adaptive evolvability includes pre-adaptations: innovative by-products of adaptation that may later become employed as needed. Crystallin, which is the transparent light-refracting protein in the cornea and lens of vertebrate eyes, originated as an enzyme. Proto-feathers arose in dinosaurs for mating display, and perhaps insulation, long before birds took them under their wing to fly.

Pre-adaptations exceed adaptations several-fold. ~ Austrian evolutionary biologist Andreas Wagner

A primary driver of adaptation is being able to take advantage of new energy sources. Metabolism exemplifies the need for evolvability.

 Metabolism

Metabolism is one of the most complex biological tasks. The metabolic genotype of an organism encodes a reaction network with hundreds of enzyme-catalyzed chemical reactions needed to consume a food source, even one as simple as a sugar.

A fundamental task in metabolism is to synthesize biomass precursor molecules from a food source as a prelude to digestion. A metabolic network is considered viable if it can synthesize all the precursor molecules it needs from its food.

There are over 5,000 biochemical reactions related to breaking down molecules for food. Any one organism employs only a small fraction of these possibilities to eat. For macrobes, many necessary reactions are performed by gut microbes in concert with host catabolic activity.

Becoming viable on a new food source allows an organism to thrive in the instance that its previous diet becomes less available. This ability often originates as a pre-adaptation.

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The forgoing examples illustrate how the genome acts as a toolkit that is intelligently and creatively employed. Evolvability is itself an integral aspect of adaptation. Pre-adaptation is a key mechanism for evolvability.