Evolution in One Page:
There is evidence that the species of plants and animals that we see on Earth today
are different than the ones that were here in the past. The change that happened to
those species is called evolution. The actual definition is the change in gene
frequency in a population over time. That means that, in the future, if a gene is more
or less common than it is today, that’s evolution.
If the gene frequency has changed so much that the new individuals can no longer
breed with the original individuals we say that a new species has evolved. Evolution
may have proceeded gradually and steadily (gradualism), but it may also have gone
long periods with no change and then had occasional sudden changes, (punctuated
equilibrium, extinction of the dinosaurs is an example of this kind).
Over the years there have been several theories advanced to explain the evolution
we observe. One famous theory thought up by a scientist named Lamarck, is the
Inheritance of Acquired Characteristics. This theory is now considered wrong. It said
that if an animal or plant that gets a new trait during its life, that trait could pass it
along to its offspring. For example, if a mother learned to read Latin, her baby would
be born with that knowledge. Or if a man lifted weights, his baby would be born
stronger. Or if a giraffe stretched his neck to reach high leaves, his baby would be
born with a longer neck. We know now that only things that change your genes can
be passed on (and lifting weights does not change your genes).
The theory we accept today is Natural Selection, first stated by Charles Darwin. This
theory is explained in 3 short statements:
 All species have more offspring than could possibly survive. This produces
challenges to survival from competition and changing environments.
 Due to natural variability in genes, some offspring are better able to meet
these challenges and they live to reproduce more offspring with those genes.
This is sometimes called “survival of the fittest.”
 The next generation therefore, will have a higher frequency of those genes
The variation in genes mentioned above, comes from things like sexual
reproduction’s independent assortment of chromosomes and random mutations,
which damage the genes (mutations are mostly caused by environmental factors like
chemicals and radiation.) Most mutations cause an offspring to die immediately, but
some mutations may not only be harmless, they could be actually helpful for survival.
For example, an animal like a dog cannot grasp a branch with a paw. But if he had a
chromosome mutation, that caused one toe to be accidentally on backwards, that toe
could act like a thumb and allow the paw to grasp the branch and maybe to even
climb a tree. This good mutation is called an adaptation, a change that allows the
dog to survive better by being able to pursue squirrels etc. This adaptation would be
passed on to the offspring, since it was in the genes. Remember, if it changes the
gene frequency, its called evolution.