Phyletic Gradualism and Punctuated Equilibrium

Phyletic gradualism is an evolutionary concept that states that evolution generally occurs by smooth, continuous, gradual transformations of whole lineages. It happens slowly over time. It would look more like this. The branches of different species would slowly turn into other ones, slowly branch off to new species as maybe they lived in different areas, as they evolved to eat different things or hunt different creatures, or react to different geological habitats.

It would happen very slowly. It would happen continually. It would happen so slowly you wouldn’t notice it, really. Punctuated equilibrium is a different concept. This evolutionary concept proposes that most species will exhibit very little change. Species will remain in stasis, or equilibrium, until a sudden event disrupts this, causing the species to evolve rapidly or perish. That would look more like this diagram.

In this diagram, any of these straight lines going up would represent equilibrium, or stasis as it is called in the theory. Then, you’ve got these corners. Anywhere there’s a corner, there was some event that caused things to change. These would be your punctuations, your punctuated equilibrium. This is where a rapid change would happen. Some big event caused change to happen, and then the rest of the time you’ve got stasis.

The species are staying the same. Nothing is changing in the world to make them have to evolve. They’re going to just stay the same until something happens. If a meteor were to hit it, would change a certain climate and it would change the area that certain species lived in, so they would have to evolve rapidly or they would perish. Those species would no longer exist.

That’s what happens in some of these lines, where you have ones that go up and then stop and it branches into two new species, or the old one stayed a little bit longer but eventually perished and couldn’t keep up, where these two species kept going after they had evolved at that punctuated stage during that rapid event, that rapid era of change. Phyletic gradualism happens gradually, slowly over time.

Events can happen, but it’s not going to have as big of an impact, because change is constantly slowly happening to species. Punctuated equilibrium says everything stays the same. The species are staying pretty much the same throughout time, except when there’s a big event and there is some rapid change that has to take place for the species to continue, or they must rapidly change and evolve so that they can keep living due to whatever big event happened.

You can remember those by equilibrium, or stasis, that stays the same for a long time and then is punctuated by rapid bursts of change, and gradualism. Phyletic gradualism is going to happen slowly continually gradually over time.