Gradualism — Definition & Examples

What Is Gradualism?

Scientists have drafted many theories and created many models to show how evolution occurs. They have also tried to understand how fast the process occurs. Currently, there are two main theories concerning the rate of speciation.

Phyletic gradualism is one theory of evolution that tries to model this rate. It predicts that species are always gradually evolving, changing very slowly over time. There is never a point where a species remains unchanging. That's because the natural world is always changing, and species must keep up in order to survive. Fitter organisms (individuals with traits that allow them to survive and reproduce better) will slowly become more common in a population. Eventually, they will replace organisms with less fit traits entirely.

According to this theory, the species that we see in the present day gradually evolved over millions of years and many generations. However, the process happens so slowly that it's impossible to see the small, gradual changes. Only millions of years later, when all the small changes start to add up, do we see the effects of evolution.

This is in contrast to punctuated equilibrium, which is the second, opposing theory of evolution. This theory says that species mostly stay the same over long periods of time. Every once in a while, we will see short periods of rapid change.

So, which theory is correct? We don't really know, but many scientists agree that it depends on the type of species and each specific ecosystem. Some also say that the real process might be a combination of the two theories.

Rate of Speciation: Gradualism

(Video) Process of Evolution | Gradualism vs. Punctuated Equilibrium vs. Catastrophism

by 2 Minute Classroom

This video compares the two theories that model rate of speciation: gradualism and punctuated equilibrium.

• Gradualism is when small changes happen over time. These changes can add up, resulting in large changes. We can observe this in the fossil record by looking at differences in similar species.

• Punctuated equilibrium is when there is a long period with no change, followed by a huge, quick change. We can also see this in the fossil record because there are often long periods of time before noticeable changes take place.

Catastrophism is a sub-component of punctuated equilibrium. It happens when natural disasters cause sudden changes in an ecosystem. Species then rapidly evolve and adapt to take advantage of available niches.

Both of the two theories above are accepted by scientists as processes for evolution. In fact, what we observe as evolution may really be a combination of both of them.