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 favouring 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 favoured
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.