White Knights and Genotypes (Part 1of 2)

Everyone knows that life is complex, but what does that really mean? Take the following fact: we can throw away a large fraction of the genes of most organisms (up to 80% in some cases), and they will live and function just fine. In science, when a fact doesn’t seem to make a lot of sense, it’s a good clue that we are dealing with deep complexity.

Andreas Wagner, one of the leaders of the new generation of evolutionary biologists, quotes Lewis Carrol’s Through the Looking Glass in a recent paper about his “White Knight hypothesis”:

“You see,” he went on after a pause, “it’s as well to be provided for everything. That’s the reason the horse has all those anklets round his feet.” “But what are they for?” Alice asked in a tone of great curiosity. “To guard against the bites of sharks,” the Knight replied…

Wagner’s hypothesis is that while we might laugh at the folly of the White Knight, his approach to life is actually used by life itself. In his book, The Arrival of the Fittest, Wagner describes the importance of robustness in our understanding of how life survives, evolves, and creates new functions and features. While a shark bite seems an unlikely problem for a land animal, if by some strange scenario the White Knight’s horse found itself surrounded by sharks, it would probably have a better chance of surviving than any other horse. He is one robust horse!

That is the explanation, Wagner proposes, for the fact that so many organisms harbor genes that are not necessary and are not generally used. A typical bacterium, living happily in your gut, munching on an unlimited supply of the sugars in your diet, has no need of genes that allow it to live on acetone, butane, or glycerol, but it has them. Just in case. Being robust means being able to survive tough challenges, no matter how unlikely – like a sudden loss of sucrose to live on, or being plunged into shark-infested waters. It means being adaptable to unexpected changes in the environment, being able to adjust and survive.

Wagner is working  on one of the long-standing mysteries of evolutionary biology: how do biological innovations arise? The early 20th century biologist Hugo de Vries pointed out that while natural selection can choose which of many variant forms of life (or enzymes, genes, or metabolic pathways) works best, natural selection cannot innovate. It was De Vries who coined the term “arrival of the fittest”, to distinguish innovation from the better understood survival of the fittest.

In several publications over the past decade or so, Wagner and his team have proposed a very exciting answer to this question – one related to the White Knight’s horse. Their hypothesis also resolves the apparent paradox of how robustness and innovation can happen at the same time.

Robustness is conservative; it maintains a homeostasis in the face of external change. This is accomplished by lots of duplication and overlap of critical functions, so that biological processes are immune from damage to any one part. That is one reason that most organisms can do just fine after losing so many of their genes. Innovation, on the other hand, is revolutionary; it implies large-scale change. How can these two opposite impulses be connected? The genius behind Wagner’s answer is the discovery that biological innovation requires robustness, and robustness leads to innovation.

In the next post we will take a closer look at how that works.

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