Though we know that populations change over time and that different species have many genetic similarities, we still have a lot to learn about how relationships between organisms affect the changes, how populations develop adaptations to survive and reproduce, and the history of life on this planet. Evolutionary biologists help us understand the stories of our past but also provide us with invaluable clues to improving public health and well-being.
Over 150 years ago Charles Darwin proposed a theory about evolution through a means he called "natural selection".
How Does Natural Selection Work?
Natural selection is a mechanism by which populations adapt and evolve. In its essence, it is a simple statement about rates of reproduction and mortality: Those individual organisms who happen to be best suited to an environment survive and reproduce most successfully, producing many similarly well-adapted descendants. After numerous such breeding cycles, the better-adapted dominate. Nature has filtered out poorly suited individuals and the population has evolved.
V.I.S.T.A. Natural selection is a simple mechanism that causes populations of living things to change over time. In fact, it is so simple that it can be broken down into five basic steps, abbreviated here as V.I.S.T.A.:
Variation, Inheritance, Selection, Time and Adaptation.
Variation: Members of any given species are seldom exactly the same, either inside or outside. Organisms can vary in size, coloration, ability to fight off diseases, and countless other traits. Such variation is often the result of random mutations, or "copying errors," that arise when cells divide as new organisms develop.
Inheritance: When organisms reproduce, they pass on their DNA--the set of instructions encoded in living cells for building bodies--to their offspring. And since many traits are encoded in DNA, offspring often inherit the variations of their parents. Now, Charles Darwin didn't know about DNA, but he did understand the basic principle that offspring inherit their traits and characteristics from their parents.
Selection: Environments cannot support unlimited populations. Because resources are limited, more organisms are born than can survive: some individuals will be more successful at finding food, mating or avoiding predators and will have a better chance to thrive, reproduce, and pass on, their DNA. Small variations can influence whether or not an individual lives and reproduces. Differences in color, for instance, aid some individuals in camouflaging themselves from predators. Sharper eyes and claws help an eagle catch its dinner. And brighter coloration improves a male peacock's chances of attracting a mate. This is how "nature selects" the survival of the fittest.
Time and Adaptation: In generation after generation, advantageous traits help some individuals survive and reproduce. And these traits are passed on to greater and greater numbers of offspring. After just a few generations or after thousands, depending on the circumstances, such traits become common in the population. The result is a population that is better suited--better adapted--to some aspect of the environment than it was before.
One of the best websites to learn more about evolution is U.C Berkley's Evolution 101 website.
Play the Natural Selection game! (requires Adobe shockwave)
PBS has a set of quick videos about Darwin and Evolution.
PBS also has an interactive exploration of the geological history of the earth called Deep Time.
Play Bioman's Snurfle Islands evolution game.
Explore natural selection with Biology in Motion's Evolution Lab.
Play Science Channel's Game Who Wants to Live A Million Years?