In chapter 7 of The Design Matrix, I have a section entitled, “Unpredictably Predictable.” The basic argument is summarized in the last sentence of that chapter:
Even though evolution is supposed to be inherently unpredictable, as we can see, it has occurred within a very predictable biological matrix.
Evolution is not some random “free-for-all” where anything that just happens to work will eventually be selected for. Evolution is a biological process that is constrained and thus channeled by the composition and arrangement of life’s machinery.
I then spell out one aspect of this evolution in a section entitled, “Designed to Redesign.” Here I talk about the essential role that gene duplication plays in the function we call “evolution”:
It is a beautiful solution for a front-loading designer. In one process, we both propagate the original design and set things up to unpack secondary designs without erasing the original design. Stability and change, all in one package. As an added bonus, the infl uence of contingency is dampened. It does not matter if some or many gene duplication events drift off in unintended fashion (most will merely tweak the original function or decay away). Th e beauty of gene duplication is that it explores sequence space while retaining and propagating the original sequence. As long as the original sequence is essentially retained somewhere, someplace, evolution gets to “try again” over and over and over in its rigged search for some future design. In other words, if a designer wanted a secondary design to unpack itself in an animal cell, duplication of the original sequence is bound to happen in all cells, including animal cells. When it eventually occurs in an animal cell, the stage is set to unpack the secondary design. If it fails, we need only wait until the next round of duplication and mutation occurs. It is the intelligent use of chance.
Over five years later, a paper has appeared in the journal Science that adds even more plausibility to my perspective. Enjoy:
Evolution, often perceived as a series of random changes, might in fact be driven by a simple and repeated genetic solution to an environmental pressure that a broad range of species happen to share, according to new research.
Princeton University research published in the journal Science suggests that knowledge of a species’ genes — and how certain external conditions affect the proteins encoded by those genes — could be used to determine a predictable evolutionary pattern driven by outside factors…… “Is evolution predictable? To a surprising extent the answer is yes,” said senior researcher Peter Andolfatto, an assistant professor in Princeton’s Department of Ecology and Evolutionary Biology and the Lewis-Sigler Institute for Integrative Genomics.
The researchers carried out a survey of DNA sequences from 29 distantly related insect species, the largest sample of organisms yet examined for a single evolutionary trait. Fourteen of these species have evolved a nearly identical characteristic due to one external influence — they feed on plants that produce cardenolides, a class of steroid-like cardiotoxins that are a natural defense for plants such as milkweed and dogbane.
“It shows that a common molecular mechanism is used by many different insects to defend themselves against the toxins in their food, suggesting that perhaps the number of potential mechanisms for achieving this goal is very limited,” he said. “That many different insects independently evolved the same molecular tricks to defend themselves against the same toxin suggests that studying a small number of well-chosen model organisms can teach us a lot about other species. Yes, evolution is predictable to a certain degree.”
The researchers found that the genes of cardenolide-resistant insects incorporated various mutations that allowed it to resist the toxin. During the evolutionary timeframe examined, the sodium-potassium pump of insects feeding on dogbane and milkweed underwent 33 mutations at sites known to affect sensitivity to cardenolides. These mutations often involved similar or identical amino-acid changes that reduced susceptibility to the toxin. On the other hand, the sodium-potassium pump mutated just once in insects that do not feed on these plants.
Significantly, the researchers found that multiple gene duplications occurred in the ancestors of several of the resistant species. These insects essentially wound up with one conventional sodium-potassium pump protein and one “experimental” version, Andolfatto said. In these insects, the newer, hardier versions of the sodium-potassium pump are mostly expressed in gut tissue where they are likely needed most.
“These gene duplications are an elegant solution to the problem of adapting to environmental changes,” Andolfatto said. “In species with these duplicates, the organism is free to experiment with one copy while keeping the other constant, avoiding the risk that the new version of the protein will not perform its primary job as well.”
The researchers’ findings unify the generally separate ideas of what predominately drives genetic evolution: protein evolution, the evolution of the elements that control protein expression or gene duplication. This study shows that all three mechanisms can be used to solve the same evolutionary problem, Andolfatto said.