Nature versus nurture? Add ‘noise’ to the debate.

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https://www.quantamagazine.org/nature-ve...-20200323/

EXCERPT: In the 1990s, an army of clones invaded Germany. Within a decade, they had spread to Italy, Croatia, Slovakia, Hungary, Sweden, France, Japan and Madagascar — wreaking havoc in rivers and lakes, rice paddies and swamps; in waters warm and cold, acidic and basic. The culprits: six-inch-long, lobster-like creatures called marbled crayfish.

Scientists suspect that sometime around 1995, a genetic mutation allowed a pet crayfish to reproduce asexually, giving rise to a new, all-female species that could make clones of itself from its unfertilized eggs. Deliberately or accidentally, some of these mutants were released from aquariums into the wild, where they rapidly multiplied into the millions, threatening native waterways species and ecosystems.

But their success is strange. “All marbled crayfish which exist today derive from a single animal,” said Günter Vogt, a biologist at Heidelberg University. “They are all genetically identical.” Ordinarily, the absence of genetic diversity makes a population exceedingly vulnerable to the vagaries of its environment. Yet the marbled crayfish have managed to thrive around the globe.

A closer look reveals that the crayfishes’ uniformity is only genome-deep. According to studies conducted by Vogt and others in the mid-2000s, these aquatic clones actually vary quite a bit in their color, size, behavior and longevity. Which means that something other than their genes is inspiring that diversity.

Common sense tells us that if it’s not nature, it’s nurture: environmental influences that interact with an animal’s genome to generate different outcomes for various traits. But that’s not the whole story. New research on crayfish and scores of other organisms is revealing an important role for a third, often-overlooked source of variation and diversity — a surprising foundation for what makes us unique that begins in the first days of an embryo’s development: random, intrinsic noise.

[...] within an individual organism, asymmetries arise between the left and right sides of the face, the body and the brain. Research is making it ever clearer that these differences can’t all be written off as unexplained environmental effects.

Which leaves noise — the random tremors and fluctuations that characterize any biological process. “Noise is inevitable,” said Andreas Wagner, an evolutionary biologist at the University of Zurich, “an inevitable byproduct of life.”

What makes noise inescapable, Mitchell explained, is that any organism is far too complex for genes to delineate, exhaustively and single-handedly, exactly how to build it. The wiring of the brain alone has to arise with relatively little instruction.

“The genome is not a blueprint,” Mitchell said. “It doesn’t encode some specific outcome. It only encodes some biochemical rules, some cellular algorithms by which the developing embryo will self-organize.” Molecules bounce around and interact in a cell, binding and pulling apart and diffusing at random. The processes that make proteins and turn genes on and off are subject to this “molecular jitter in the system,” as Mitchell calls it — which leads to some degree of randomness in how many protein molecules are made, how they assemble and fold, and how they fulfill their function and help cells make decisions.

As a result, it’s perfectly natural that development, the complex process that turns a single cell into an entire organism, would be “a bit messy,” Mitchell said... (MORE - details)
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