As powerful as Darwin's theory was, it had at least one major flaw. Not really a flaw; more like a gap. In order for natural selection to work, parents had to be able to pass their features on to their offspring. While it seemed obvious that this did happen, in Darwin's day there was no explanation known for heredity.
Actually, that's not quite true. The basis of the solution to the problem of heredity was actually proposed and published in 1865, by a mathematician and Augustinian monk named Gregor Mendel. While this was six years too late for the original Origin of Species, it was in plenty of time to influence later editions of Darwin's great book.
Unfortunately, Mendel's statistically based explanation went completely over the heads of those to whom it should have been most interesting, and his ideas were lost until 1900. Mendel is one of the few true examples of that old canard, the "man before his time."
Darwin never knew about Mendel's work, though he actually owned the journal in which Mendel's paper was published. Evidence strongly indicates that Darwin never read it. Too bad; it could have answered a number of Darwin's questions, though it would undoubtedly have introduced a few new ones.
Darwin died before Mendel's concepts were rediscovered. So did Mendel, for that matter a little intellectual tragedy. But these two huge innovations evolutionary theory and genetic theory met head on in the early part of the 20th century.
Wait a minute! Didn't I just say that Mendel's ideas were the only thing missing from Darwin's theory? Not quite. In the early days of the 20th century it actually seemed like these two great theories were opposed to each other. Here's where the problems came from.
The new science of genetics demonstrated clearly that traits were passed from parents to child each offspring received a combination of traits from the two parents. But what the geneticists were saying was that the traits that parents possessed were mixed and matched, new combinations were created, but that the genetic factors themselves genes remained unchanged through the generations. In other words, any new appearances were not the result of new genetic information, they were the product of reshuffling old genes.
This was not good news to the Darwinists. For evolution to work, it must be possible for new traits to arise that had never been possessed by the species before.
So that was the difficulty. The Mendelists said traits didn't change, they just got shuffled into new combinations. The Darwinists insisted that it must be possible for totally new traits to arise. During the first few years of the century, this conflict created a real schism in the ranks of biologists.
Of course, no complex concept is born fully fledged they all develop
and grow as we learn more and more. This has certainly been true of the
concept of evolution, and it was also true for our understanding of heredity.
In the second decade of the 20th century, some geneticists began to devote
more and more time to the study of mutations. Mutations are permanent
changes in genes. Initially, geneticists thought that all mutations were
harmful; as they learned more, they saw that this was not true. So genes
could change and the changes often caused no change other
than an increase in diversity, and sometimes actually produced improvements.
Eventually, the two sides in this artificial division of the science of biology hammered out their differences, and produced a new and improved version of the theory of evolution which incorporated modern concepts of genetics and finally filled the only significant hole in Darwin's original theory. This modernized version of the theory of evolution is called the New Synthesis, or Neo-Darwinism.
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Updated 25 September 2004