Arrival of the Fittest
This important book by Andreas Wagner dives into the mechanics of evolution beyond what we all know (random genetic changes combined with natural selection lead to innovation). It answers the following questions: Isn’t a mutation much more likely to destroy an organism than it is to benefit it? And therefore, are even evolutionary timescales sufficient to bring about positive changes?
This omits an important third possibility: that the mutation is neither harmful nor beneficial. When you think mutations, don’t think about a birth defect. Proteins, the all-purpose machinery of life, can survive about two thirds of random amino acid changes without changing their function. They are “robust”, in biological terms.
This kind of genetic diversity will accumulate even in asexual populations. And it has an important effect: it makes more beneficial mutations accessible to the population. Random walks across the neutral parts of the mathematical space of possible genetic sequences – what Wagner calls genotype networks – can lead to life’s next innovation.
Microbes are masters of this kind of innovation. They can walk across genotype networks much faster than humans can, since they reproduce so rapidly. They can pass these innovations along through horizontal gene transfer. And in many cases, they themselves become incorporated into larger organisms.
Once that happens, they may lose their original versatility, which is no longer required. Wagner cites the example of bacteria that have entered a symbiotic relationship with aphids (plant lice). These bacteria live inside protected structures called bacteriocytes and have lost much of their genetic complexity. Thus, it would be hopeless to expect them to magically adapt to dramatically different circumstances: they would just die, like humans deprived of oxygen. Life’s robustness is itself an adaptation to the environment in which evolution operates.
Wagner explains these concepts in the context of the evolution of metabolism, gene regulatory networks, and proteins, using the latest scientific knowledge. He makes a compelling case that all life follows beautiful mathematical rules that go beyond natural selection and random change, and that those very laws make evolutionary innovation inevitable, provided there is (the name of the first chapter), “world enough, and time”.
As he makes clear repeatedly, these insights do not take away from Charles Darwin’s remarkable discoveries, or from the modern evolutionary synthesis of the 20th century. They sharpen our understanding of how evolution works. My only criticism of this fine book is that it itself does not provide more of a synthesis of these ideas with other concepts, like symbiogenesis or the evolution of sexual selection. Instead, it provides compelling evidence for the importance of genotype networks for what Wagner calls “innovability”. I consider it (and the research behind it) a step along the way to a 21st century synthesis.