Arrival of the Fittest: Solving Evolution's Greatest Puzzle Read Online Free Page B

trillions of cells, each inhabited by billions of molecules whose functions are themselves incredibly complex. And they neglected how all this complexity unfolds from a single fertilized cell, and how genes contribute to this unfolding. By neglecting this complexity, the architects of the modern synthesis effectively ignored its product: the organism itself. They did so knowingly, since they wanted to understand how gene frequencies change over time. In focusing on the genotype, they simplified an organism’s phenotype down to simpler quantities, such as
fitness,
the average number of genes a typical individual transmits to the next generation. (Fitter organisms contribute more genes to the next generation’s gene pool.) What is more, they also assumed that individual genes play a simple role in determining fitness, for example that fitness is the sum total of many small gene effects.
    Don’t get me wrong. It is hard to see how the modern synthesis could not have ignored the organism. The price of understanding is always abstraction, neglecting most of a staggeringly complex world to understand one tiny fragment of it. Take it from another theorist, Albert Einstein, who knew what he was talking about when he said that “everything should be made as simple as possible, but no simpler.” 32 The modern synthesis was just as simple as it needed to be to answer thousands of questions about the evolution of genes and genotypes. Its very success in understanding natural selection in action was built on getting rid of organismal complexity. But whenever a theory is successful, it is also easy to forget its limitations, and this is exactly what happened in the heyday of the modern synthesis, when the grandeur of life’s evolution became redefined and demoted to a “change in allele frequency within a gene pool.” 33 The principal limitation—a high price to pay—was the inability to answer the second great question the
Origin
had left open: Where do innovative phenotypes come from? The modern synthesis could explain how innovations spread, but not how they originate.
    To say that all evolutionists had thrown the organism under the bus, however, would be unfair to a minority of them, those who compared how the complexity of different organisms unfolds in their embryos. But these embryologists, whose forebears had helped Darwin to recognize the common ancestry of all living things, were sidelined by the modern synthesis and its advocates, who had no need for the embryo. In 1932, one year before he would win the Nobel Prize for showing how genes are organized into chromosomes, the fly geneticist Thomas Hunt Morgan would say that it does not matter much “whether you choose an ape or the foetus of an ape as the progenitor of the human race.” 34
    But even though population geneticists ruled in biology’s halls of power, some embryologists in the back rows kept heckling the opinion leaders, pointing out that they were ignoring the very thing they were trying to explain. Their voices got louder toward the end of the twentieth century. That’s when evolutionary developmental biology, or “evo-devo,” emerged as a new research discipline, one that aims to integrate embryonic development, evolution, and genetics. Evo-devo produced fantastic insights into how genes cooperate, like orchestra musicians, to make embryonic development possible.
    So far, though, these insights have not yet added up to a theory rivaling the modern synthesis. And only theory can turn a heap of facts into a tower of knowledge. The culprit is once again the enormous phenotypic complexity of whole organisms. Even today, we struggle to fully understand the phenotype of even the simplest organisms, and hundreds of thousands of biologists laboring over many decades have still not fully understood how genes help shape this phenotype. 35 Where the modern synthesis has a theory without phenotypes, the embryologists have phenotypes without a theory.
    Evo-devo,