Theories don’t last in science. A scientific theory is a model that explains, based on the existing evidence, how some aspect of the universe works. When new evidence is discovered it can blow the existing theories apart and help build an entirely new one. A classic example is Newtonian mechanics. Sir Isaac Newton was the first person to develop a theory of gravity, one that’s still taught in physics lessons today.
The only problem with Newton’s theory is that it’s wrong. It still describes gravity accurately enough that NASA could use it to put a lander on the moon, but nevertheless it’s wrong. In the early 20th century it was replaced by Einstein’s theories of special and general relativity. These are a more accurate model of how physics works at a large scale – but they clash badly with quantum mechanics, a theory which describes how physics works at a small scale. Sooner or later a new theory will unify them and the old ones will fade away.
Charles Darwin’s theory of evolution by natural selection has not faded away, and isn’t likely to, for a very simple reason: Darwin was right. That’s not to say his original theory was perfect, because it wasn’t. There were large gaps in it, because 19th century science just wasn’t capable of finding some key pieces of evidence. There are many minor errors in the deductions he made from the evidence he did have. There are even raging debates about the level evolution happens at – does it occur at the level of individual organisms, as Darwin assumed, or among groups as advocated by V.C. Wynne-Edwards and Karl Lorenz? The group selection idea began to fade away in the 1960s but a decade later a new argument erupted, in the shape of the gene-level view popularized by Richard Dawkins.
Some opponents of evolution point at these scientific debates as evidence that Darwinian evolution is flawed, “a theory in crisis”. Actually they’re nothing of the kind. Biologists might argue about whether natural selection – the engine of evolution – acts on animals, genes or populations, but they’re all firmly united on one vital point – natural selection acts.
Almost as soon as Darwin set his complete theory down on paper it began to change. He was responsible for many of these changes himself; Origin of Species went through six editions in his lifetime, each one refining and adding to the original model. The biggest change came decades after his death, in the 1930s, when the one yawning gap in the theory was filled.
Darwin knew that living things could inherit characteristics from their parents, but he didn’t know how. The answer came from a Moravian scientist, Gregor Mendel, who had died in 1884 – only two years after Darwin himself. Mendel had studied the inheritance of characteristics in peas, and beginning in 1918 his work was expanded into the new field of population genetics. This was then progressively unified with Darwin’s work by Dobzhansky, Mayr, Ford and others; the end result was what Julian Huxley – the grandson of Darwin’s friend Thomas – named “the modern synthesis” in 1942.
Seven decades later even more gaps have been filled in. Scientists have discovered and studied DNA, the raw material of genetics. The roles of mutation, geographical separation and symbiosis have all been examined and discussed. The theory of evolution has expanded and developed to take in ideas that, in Darwin’s time, were beyond comprehension. But its keystone – the single component without which it would all fall apart – is the principle of natural selection.
It’s impossible to overstate the importance of natural selection. Take away that single insight and almost nothing in modern biology makes sense. Darwin’s understanding of natural selection has led to huge advances in artificial selection, and now in genetic engineering: his work gives us the tools to develop new crop varieties or beneficial bacteria, using methods that he couldn’t even have imagined. The alarming problem of antibiotic resistance – the growing ability of many bacteria to survive treatment with antibiotics – has a Darwinian explanation. It’s not clear if there’s an effective solution, but all the potential ones are underpinned by Darwin’s idea.
Coping with resistant bacteria isn’t the only medical use of natural selection. Selective breeding of blind Mexican cave fish has managed to produce offspring that can see; this has helped researchers identify the genes responsible for vision. In the future some kinds of blindness could be reversed by targeted gene therapies, and the research that makes it possible has its origins in the study at Down House.
Natural selection has even been pushed beyond the world of biology altogether. “Evolution strategies” have been used to solve problems in engineering, electronics and software design, by running through computer-modeled solutions that are allowed to randomly “mutate”. In many fields this approach is faster and cheaper than traditional methods, especially for debugging software.
Modern biology is cutting-edge science, using the latest technology to observe living things in the wild or study them down to the genetic level, but it’s all based on a single theory. That theory is evolution, and the heart of it is one incredibly powerful idea; natural selection. Darwin’s theory has developed beyond his wildest dreams in the last century and a half, to become the foundation of everything we know about living things – including ourselves. It’s hard to imagine how a theory could be more important, and the unifying insight that ties it all together belongs to Charles Darwin.