The modern synthesis- Evolution as we now know it
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Charles Darwin first outlined his theory of evolution by natural selection in the 1850s – but 40 years later, biologists were still arguing about its merits. At the turn of the 20th century biologists began to recognize the important role that genetics play in evolution, eventually realizing that genes supported Darwin’s views on evolution and leading to what is called the modern synthesis.
Just a few years after Darwin published On the Origin of Species, Gregor Mendel began experimenting on pea plants and exploring the way organisms inherit features from their parents. Mendel was ahead of his time – it wasn’t until the 20th century that biologists took his ideas seriously and the study of genetics began in earnest.
But it was vital that they did. Genetics provided a missing piece in Darwin’s theory – a mechanism through which characteristics could be inherited. Even so, many early geneticists thought their work actually disproved Darwin’s ideas. Genes were discrete chunks of heritable information, and they seemed to imply evolution occurred in abrupt leaps: if a gene for “tallness” emerged, for instance, then a population might evolve rapidly into a new “tall” species. Darwin had insisted that evolution was slow and steady, with new species evolving gradually.
But as geneticists began to probe more deeply they changed their minds. In the 1920s they discovered that a feature like “tallness” is often coded by dozens of genes, not just one. Scientists like Ronald Fisher, J B S Haldane and Sewall Wright began to produce mathematical models to explore how populations might evolve if one or more individuals happened to be born with a beneficial new genetic mutation. They realized that genetic complexity led to a pattern and pace of evolution that was perfectly compatible with Darwin’s concept of natural selection. More than 60 years after the publication of On the Origin of Species, biologists had finally accepted Darwin’s ideas.
One of the key revelations of the modern synthesis was that biological features are often controlled by dozens of genes, not just one. This simple discovery helped explain how discrete, binary genes can build organisms that seem to seamlessly blend features from both parents and evolve gradually into new forms. A computer game character looks blocky when it is drawn on a 12 by 16 pixel grid but super-smooth if it is drawn using thousands of pixels: similarly, an organism – and evolution – has a “smooth” appearance because organisms are often built from thousands of genes, not a mere handful.
The modern synthesis showed how evolution by natural selection works through genetic inheritance.
It represents the moment that biologists agreed about what evolution is and how it occurs.