Punctuated Equilibrium: What Causes It?

Over the years, as more fossils have been unearthed, one glaring puzzle dominated the discussion.  And that is the absence of evolutionary links between the existing fossils. Not just THE missing link, but LOTS of missing links. One explanation has been "punctuated equilibrium" - which means there are periods of rapid appearances of new species (punctuation) followed by eons of no change (equilibrium). It caused a lot of debate mainly because the proponents,  Niles Eldredge and Stephen Jay Gould, did not provide a satisfactory cause.

But I propose there is a cause. Read on.

The cause of punctuated equilibrium is continental shift? (Read about what causes it here: Cataclysmic Continental Shifts: What Causes Them?)

In short, the fossil record only preserves the animals that are alive at the moment of a cataclysmic continental shift. Because the only life preserved are those that are rapidly buried by the widespread silt-laden floods associated with these periodic catastrophes. This is a record of the animal and plant life that lived at the end of the long periods of calm, where the continents drifted slowly, or remained static.



But then comes a time when the tectonic plates shift violently. The volcanic activity at the plate boundaries darken the skies and poison the seas. The earth's crust buckles, adding height to mountain ranges and creating new valleys.  Continents may sink and ocean floors may rise. The earthquakes, volcanism, toxic rain and widespread flooding kill the majority of our planet's species.

The surviving plants and animals pioneer the new planet and begin to evolve rapidly to fill the now-empty ecological niches. Lifeforms that are born with a mutation that are now better suited for a different niche than their parent stock, diverge from their parents and thrive to pass on that trait in that empty and available niche.

Adaptions work like the image on the left, not the right.

Many new species are born. However, once a niche is dominated by the most efficient species, this sporadic evolution or "punctuated equilibrium" stops.

Why? Because any new individual born with a mutation will die off prematurely because it cannot compete with well-established species in either their parent's niche or another one. Neither the successful or unsuccessful mutations are captured in the fossil record because when they die they are NOT buried rapidly and deeply. All trace of them disappears due to scavenging and decomposition. Fossils are only created during a cataclysm - local or global.

Beaks of the same finch adapted to the food in their niche.

Darwin observed this process of punctuated equilibrium on a small scale among the finches on the Galapagos islands. When the birds arrived on the islands, they had no competition for the various niches, so new species filled them rapidly - whereas the parent stock of finch on the South American mainland remained one species due to the continent already having a plethora of more efficient fauna competing for the niche that a new mutation would vie for.

Gould and Eldridge argued that rapid speciation best occurs in small and isolated populations and THAT is the key to rapid and diverse change. They hypothesized that it is the species as a whole that is the driving force for change, not the random mutation of individuals. What they didn't offer was what changed in the world to create small and isolated populations.

Well now you know.

The aftermath of a cataclysm is the epitome of small and isolated populations, soon to rapidly diversify and fill the many now-empty niches of the new ecosystem. A blank canvas for new lifeforms.