The scientific Theory of Evolution explains how life forms develop and diversify over generations. Something to understand straight away is that it doesn't claim to explain the development of the universe or how life was first begun. It explains how new varieties of life form emerge from earlier life forms. Even if life on Earth had been initiated by some kind of divine or alien intervention, that wouldn't affect the evidence for evolution, which is accepted by people who believe in one or more gods, as well as those who don't. It's also important to understand what a scientific theory is. Outside science, people often use the word 'theory' to refer to a hunch or unsupported personal opinion. This is not what the word means in science. In science, a theory refers specifically to a well-substantiated explanation which accounts for a body of well-substantiated facts. So whenever we encounter a statement like Evolution is just a theory, not a fact, this tells us that whoever's made the statement is not using the terms correctly.

In science, theories don't get promoted to facts; facts are explained by theories. Because of their explanatory power, theories are the ultimate goal and the ultimate achievement in the sciences of nature. To start with some well-known facts: We know that physical traits of parent life forms are inherited by the next generation and that through the artificial process of selective breeding, many traits can be exaggerated in later generations. This can be achieved fairly simply by mating together individuals that exhibit those traits most strongly and repeating this process with successive generations. Breed only from horses with good competition records, and their offspring will tend to perform well also. Breed only from aggressive dogs, and their offspring will tend to be aggressive. Many who happily acknowledge this kind of artificial selection are the same people who label evolution 'impossible' or 'a fairy tale,' and yet natural selection, one of the major mechanisms that drives evolution, requires no magical suspension or violation of physical laws.

It simply says that traits also emerge - and reproductive opportunities are also limited - because of factors other than human influence. If a greyhound breeder selects only the fastest dogs for breeding stock and in the wild, only the fastest gazelles outrun their predators and survive to reproduce, then both nature and the greyhound breeder are favoring certain individuals for reproducing offspring and passing on their genetic information to the next generation. Before I say more about natural selection, I want to mention another commonly misunderstood term: mutation. Many think that when biologists talk about mutation, they are referring only to dramatic malformations like animals with extra limbs or heads or far-fetched scenarios like dogs producing cats, or even morphing into cats. These are misconceptions. Mutations are simply changes in genetic variation within a population brought about by insertions, deletions, and recombinations of the DNA sequence. But mutation isn't the only cause of variation

because it's not only the DNA sequence that's important to evolution. Epigenetic studies, for example, show that genes can be switched on or off and that this genetic activation or inhibition can be inherited and expressed in later generations. Most variations are neutral and have no impact on an organism's survival, accumulating naturally over successive generations in what's known as 'genetic drift,' the effects of which are far more noticeable in smaller populations. But a variation in colour, for example, could have a major impact. Take this insect. If genetic variation makes some of its offspring less conspicuous to predators, they'll have a greater chance of surviving and reproducing, and in the course of time, the insects with this variation may become more abundant within the population. If the variation makes other offspring MORE conspicuous to predators, they may not survive to reproduce, and the variation may vanish or become suppressed because of natural selection. Many who don't understand evolution

try to discredit it by equating it with 'pure accident', but it's not pure accident that camouflage, hooves, petals, antennae, fins, wings, eyes, and roots have evolved in the natural world. All these physical traits have served specific functions in contributing towards different organisms' reproductive success, and clearly, if the organisms that exhibit these traits manage to reproduce, they perpetuate their genetic information, including the information for the traits, in the next generation. But it's not true that every single trait of a living organism must be advantageous. For example, traits that give no particular advantage can still be favored if they're associated with other traits that do. When it comes to beneficial traits, there's no 'one size fits all'. Bulk may be a great advantage for a walrus wanting to dominate its rivals, but it would be a distinct disadvantage to a spider monkey that's adapted to a life of swinging nimbly through trees.

Again, it's no accident that walruses have evolved to be bulky, and spider monkeys have evolved slender, supple limbs. These physical attributes have helped them operate in their respective environments and ways of life, to survive and compete for reproduction. People who say that evolution is all about impossibly unlikely accidents and blind luck often like to claim that the probability of life forms evolving is the same as the probability of winning the jackpot on a one-arm bandit hundreds of times in a row. But miraculous accidents are the opposite of what evolution is about. If we're going to use the one-arm bandit analogy, then evolution presses the HOLD button on almost all symbols on every pull of the lever. Starting with a word, we only need to change one of its letters to turn it into a new word. Changing one letter from this word results in further new words, and if we carry on repeating the process, we can produce words that differ dramatically from the original.

Dramatic change can be achieved one small step at a time, and this is what happens with evolution, except that with evolution, countless mostly minute changes have accumulated over millions of years. If members of a given species become geographically isolated from each other, each group may end up having to respond to very different environments and predators and adapt to very different ways of gathering food. Any genetic variations will no longer be shared throughout the whole population but only within each group. In this way, genetic drift and natural selection can lead to the emergence of two distinct populations which, after a given period of time, are no longer related closely enough to interbreed. The Theory of Evolution doesn't say that organisms from one species population suddenly produce organisms from another. Dogs don't produce cats. Nor does it say that individual organisms change species. Individual apes don't morph into humans. While we're on the subject of apes and humans, there's a common misunderstanding about our evolutionary relationship with apes.

revealed by the question, If humans evolved from apes, why are there still apes? Firstly, humans didn't evolve from the apes we see today. Humans and modern apes share a common ape-like ancestor different from both modern animals. But secondly, when one life form evolves into another, that doesn't mean the first life form has to stop existing. Take life form A, so well-adapted to its environment that it changes very little from one generation to the next. But then part of the population spreads to a new environment, where it's poorly suited. Different survival pressures now lead generations of this separate population to change dramatically while the changes in the first population remain barely noticeable. After many generations, Population One still exists in more or less its original form alongside the now very different Population Two. It didn't have to die out or change at the same rate. The Theory of Evolution has never demanded the existence

of animals with a crocodile's head and duck's body. Even when there's evidence that one animal evolved directly from another, that doesn't mean the transitional forms must look like whole chunks of each animal stuck together. Evolution doesn't work by combining different species at random, and evolutionary scientists have never hunted for the crocoduck, the jellywolf, or the rhinopus. The Theory of Evolution tells us something very different. Nature doesn't reward just any random combination of features. Even highly specialized animals are being driven to extinction all the time. Nature rewards only whatever is efficient at reproducing itself. The crocoduck, invented to ridicule evolution, has instead become the symbol of bad arguments against evolution. Some people feel that an acceptance of evolution implies or leads inevitably towards the desire for supremacist control over the breeding of human beings. But recognizing facts about nature doesn't mean you have any wish to apply them to social policy and commit gross violations of human rights.

Evolution isn't an endorsement of eugenics any more than accepting the fact that the females of numerous species kill and eat the males after mating is an endorsement of cannibalism. It's simply a recognition of reality. If someone tells you that the Theory of Evolution says any of the following, then they either simply misunderstand it or they're deliberately misrepresenting it and trying to create confusion about science in the hope that this will lead to more support for their position. Either way, attempts to make evolution seem like a fairy tale by both the misinformed and the dishonest will continue to be exposed. The real fairy tale is the claim that evolution has anything whatsoever to do with dogs giving birth to cats, individual animals morphing into other species, or popping into existence through pure accident. If you speak to anyone who knows about and accepts evolution, you'll find that these ideas are as ridiculous to them as they are to the anti-evolutionist. Evolution is both a fact and a theory.

It's a scientifically established fact that life evolved and continues to evolve, and the Theory of Evolution explains how it does so. There are many reasons it's important to understand evolution, not least because evolution is essential to our understanding of biology. And with viruses quickly evolving resistance to our existing defenses, our failure to understand those processes will mean a failure to understand some of the most deadly threats we face. Because of the curiosity and careful, dedicated work of generations of scientists, we now understand, in greater detail than at any other time in our history, answers to some of our biggest questions about life on this planet. They are a key part of the scientific inheritance we are wise to pass on to new generations, who - with an honest, first-rate science education - will in turn no doubt refine our education with their own outstanding insights.