We’ll start with a quote from the Bruce Lee movie, Enter The Dragon, “When the opponent expands, I contract. When he contracts, I expand.”
Evolution is a lot like that.
Definitions:
The Theory of Evolution: The process by which life changes and adapts itself over long stretches of time. The unifying theory of biology. The most commonly accepted explanation of “biodiversity,” or the reason there are so many different yet seemingly related species on earth.
Evolutionary time: The amount of time it takes for meaningful large scale changes to occur in a species. Often measured in millions, tens of millions, or hundreds of millions of years.
Variation or mutation : Changes in a species’ DNA at each generation. May be harmful, neutral, or beneficial.
Natural Selection: The mechanism by which evolution occurs. Simply, lifeforms who are more capable of surviving and passing on their genes will slowly overcome less capable lifeforms of their own species.
Reproduction: One generation creating the next generation and passing on their traits through DNA.
Genetic Drift: changes in the total number of possible traits due to having two parent’s DNA combined randomly every time two creatures reproduce. It can remove or switch up what genes possibly go to the next generation.
Species: A lifeform where any breeding pair (one male and one female) can produce offspring who can themselves produce offspring. Ex: Horses and donkeys are separate species whose mating produces mules, who can not reproduce further. Mules are therefore not their own species.
The basic process of evolution is very simple: A creature lives, does stuff, and dies. If that stuff included producing a new generation, the potential for evolution to start occurs. It’s children repeat. And so on. Over the next few million to hundred million years each generation’s changes build up over the last creating bigger and bigger changes until the creature would no longer be able to mate and produce virile offspring with it’s ancestors. Over a long enough timeline, it is theorized this process could be responsible for all life on earth.
The Bruce Lee quote comes in with natural selection. When Darwin first theorized about it, Artificial Selection had been used for years to breed better plants and animals (this is why we have so many breeds of dogs and corn has gotten several times larger since europe found it).
Artificial selection works like this: A person decides a trait they want in another creature (say speed and endurance in a race horse). The person then finds two fast horses who can run for a long time and breeds them over and over again. Some of the offspring of those two horses are a little faster or a little slower and can run for a little longer or a little less long. The offspring who can run faster and for longer are bred with other fast high endurance horses. Over time, this has bred some very, very fast horses.
Natural selection is similar, except instead of a person choosing the environment does. Rather than use a complex real world example, let’s go back to the Bruce Lee quote, modified to fit this context better:
“When the environment expands, I contract. When it contracts, I expand.”
So, in an environment where one must react to something expanding by contracting and vicaversa, traits that would help a creature survive would include the ability to recognize if things are expanding or contracting, what the right response to it would be, and expanding/contracting itself. And the speed at which these happen.
Thus, a creature who could change to the conditions of an environment as nesscesary will survive in that environment better than one who can’t adapt as well. This is why large scale climate changes inevitably create massive extinction. One or two generations is usually not enough time to adapt to a radically different environment.
And even after factoring mutation and genetic drift (the main random elements of evolution) the final “survive or die” chances of a species is how well it can adapt to the environment at hand, whatever that may be.
There is much, much more to evolution than this simple overview, here is a short list of possible books you may want to check out to get a better understanding of the subject:
http://www.mit.edu/~ejhanna/sci/evobook.html
