Artificial and Natural Selection
by Ellie Maclin, Demand Media
Natural and artificial selection both involve genetics and the way species survive.
When a population's environment acts on that population such that well-adapted individuals thrive and poorly adapted individuals die out,
that's natural selection. Artificial selection, on the other hand, happens when people take the place of natural processes and breed plants or
animals for particular traits. Natural selection and artificial selection both refer to processes that change traits in living species from one
generation to the next.
THE ROLE OF "FITNESS"
Whether you're talking about natural selection or artificial selection, "fitness" is important in different ways. Fitness describes the ability of
an individual to live successfully in its environment. If most insects in a population are black, but a few are born red, the red ones would be
more fit in an environment of red rocks. The black ones would stand out and be spotted by predatory birds, while the red ones would be
camouflaged and survive. If the red ones lived to breed, but most black ones did not, the trait for red coloring would rapidly spread in that
species' gene pool. Most of the surviving population could be red within a few generations.
NATURAL SELECTION
For natural selection to occur, there must be diversity -- that is, a range of different traits -- within a population. That variation must directly
impact individuals' ability to survive, as in our example of red and black insects above. Those traits must be genetically heritable -- in other
words something a parent can pass on to offspring. In natural selection, the difference in reproductive success based on a particular trait is
driven by natural processes like predators, weather conditions, and environmental constraints. Natural selection is purely situational -- it has
no will or purpose. It's simply "cause and effect" in action.
ARTIFICIAL SELECTION
Artificial selection is imposed by humans on other organisms. People apply selective pressure by choosing to modify particular traits to
achieve a purpose, as in selective breeding for pet traits or increased yield and nutritional value in plant foods. Artificial selection, by
definition, involves will and intent, as humans seek to alter other organisms. Artificially selected traits do not necessarily improve fitness, as
with natural selection, but rather encourage a trait that is fit for the purposes of people. Today, some scientists are taking artificial selection a
step farther with the introduction of genetic modification. Genetic modification takes place at the level of DNA, where -- for example -- a
particular gene can be extracted from an animal species and inserted into a plant species. This is how herbicide-resistant crops were created.
CONCERNS ABOUT ARTIFICIAL SELECTION
As far back as 1908, scientists had concerns about artificial selection practices. While natural selection relies on diversity and keeps the fittest
members of a population in direct contact with the rest of their peers, artificial selection removes the most desirable members from the rest of
the population and encourages standardization to the point where diversity is no longer possible. Because humans have helped purebred dogs
survive and breed, for example, some undesirable traits like narcolepsy and hip dysplasia have become characteristic of particular breeds.
The debate over artificial selection has risen to new levels with concerns over genetically modified crops. The American Academy of
Environmental Medicine has called for a moratorium on GM crops until their safety and efficacy has been ascertained, saying GM foods may
"pose a serious health risk in the areas of toxicology, allergy and immune function, reproductive health, and metabolic, physiologic and
genetic health."