Before jumping onto the two contradictory concepts of the rate of evolution viz., phyletic gradualism and punctuated equilibrium, let’s talk about transitional fossils first. To put into simple words, these are remnants of an organism that came in between a known version of a species and the current species. However there are missing transitional fossil forms too, which are gaps in the fossil records between any animal and its supposed evolutionary ancestor.
Allegedly, transitional fossils would be evidence for phyletic gradualism as they show intermediate forms of a species and how they changed and accumulated adaptations at a slow pace.
Unfortunately, since the fossil record is incomplete, there are many missing transitional fossils that could silence the concept of phyletic gradualism and possibly supports the model of punctuated equilibrium which states that instead of a gradual change, there are periods of rapid change, followed by periods of relative stasis.
Punctuated equilibrium is based on the idea that we cannot see changes in a species, so there must be very long periods of no changes of species. That is the equilibrium part of punctuated equilibrium. However, we do know that species do change, so there has to be a period of time where those changes occur. Punctuated equilibrium asserts these changes over a relatively short amount of time “punctuating” the long periods of equilibrium.
Strangely enough, the fossil record is also cited as evidence for punctuated equilibrium even though it is also given as evidence for gradualism. Proponents of punctuated equilibrium point out that there are many what are considered “missing links” in the fossil record. If punctuated equilibrium is the correct model for the rate of evolution, those links never really existed to begin with, so that removes the issue of missing links in evolution.
At this time, neither hypothesis is considered more correct than the other. More evidence will be needed before either gradualism or punctuated equilibrium will be declared the actual mechanism for the rate of evolution.
deptt of zoology
university of rajasthan