Scientists Explain Evolution Can Take Millions of Years — But Here’s Why Some Species Haven’t Changed at All

The modern human species, Homo sapiens, has only existed for an estimated 200,000 to 300,000 years. However, hominins, which include our direct ancestors, and ancient extinct relatives like Neanderthals, have been evolving for millions of years. This idea is probably why when people think of evolution, they imagine slow, steady changes over countless years.

The concept might be true, but that is not nearly the full story. There are some species on this planet that look like they never changed at all, and thus were dubbed the title, “living fossils”. Crocodiles seem to still be physically the same as they were when the dinosaurs roamed the Earth, or Coelacanths, who are currently swimming the seas with fins that evolved longer than any mammals have existed.

But have they really stopped evolving? After millions of years in existence, with no visible changes at all, why do these creatures appear to be frozen in time? The answer lies in how we understand evolution, and why, sometimes, no change is not bad at all.

The Public Perception of “Living Fossils”

Many people believe that species like crocodiles simply stopped evolving and are “living fossils”, and at first glance, this idea sounds right. After all, the crocodiles of today still look a lot like their ancestors. The same story goes to the coelacanth, which was once thought to be an extinct species for millions of years and was even displayed in museums, only for it to be rediscovered with the same features.

However, the very idea of “living fossils” is a misconception and scientifically misleading. While the term was coined by Charles Darwin himself, it is very oversimplified and fails to communicate the complexity of ongoing evolutionary processes. This is because all living organisms, even those that are dubbed “living fossils,” are still evolving at a genetic and molecular level that the eyes could not perceive.

So, in other words, the truth is much more complex. These species are still evolving, only at a slower or subtler rate. Externally, their bodies may have still looked the same after millions of years, mainly because natural selection has not pushed for any more major changes due to their species’ success at survival and reproduction.

Read more: Wikipedia

Crocodiles Show Us Evolutionary Equilibrium

Crocodiles - Myth of the Living Fossils

Crocodiles are a great example of evolution and the concept of “living fossils”, which, as stated, was scientifically misleading. Fossils show that crocodylomorphs, crocodiles’ ancestors and lineage, were once very diverse, both internally and externally. There are some that ran with long legs on land, others swam in the oceans with their flippers, and a few more variations.

But the point is, over millions of years, a certain body type wins out, which is the semi-aquatic reptile predator. This is an external body that was so successful in surviving and thriving in their environments that crocodiles look like they barely changed for over 80 million years.

In reality, their genes have continued to shift and have undergone several evolutionary changes, and even diversifications to multiple other species, like alligators. So, they are not a flawless symbol of evolution; they have just become so successful that no major shift that could make them look really different in our eyes has needed to happen.

Other Masters of Stasis — Coelacanths, Gars, and Horseshoe Crabs

Let’s explore a few more species that were dubbed the scientifically misleading term of “living fossils”. First, there is the coelacanth, which experts thought was extinct, but they found one in 1983, which completely changed its history in our books.

It has a feature that survived for 400 million years, its fins that move like a limb. But, since it lived underwater, in the deep sea caves and thrived there, the species remained stable with little pressure to change drastically.

Another is the horseshoe crabs, which have ancient blue blood and an armored shell. A species that survived five different major extinction events on Earth. For over 300 million years, it seems to have never changed at all, but externally, why would it? It is already pretty good at survival and reproduction.

Read more: WIRED

Why Stasis Happens — and Why It’s Not Really “No Evolution”

The Species That Broke Evolution?

Evolutionary stasis and no evolution at all are completely different ideas. The species we mentioned, along with all the others dubbed as “living fossils,” are just in stasis, and here are the reasons why.

They have stable environments that have not changed much at all. Examples include the deep ocean or tidal flats, where coelacanths and horseshoe crabs exist. Without much challenge in an environment, the pressure to change is not as high.

Species like crocodiles and sharks have already found the best and optimal body plans. It is so efficient that major changes could affect their success, and result in the opposite direction instead. There is a phenomenon called punctuated equilibrium, which describes that a species could have periods where it did not change much for a very long period of time, but when exposed to new environments, it can quickly change.

Slow genetic change is also normal for some species, like the Gars, which means that they accumulate mutations over time slower than others, making them look like they never change at all.

So, in other words, these creatures that are called “living fossils” may look very ancient, but evolution has not stopped for them. It just slowed or shifted in ways we could not directly observe with our own set of eyes.

Author's Final Thoughts

Evolution could take millions of years, but it does not always mean that after a specific amount of time, a species will have changed so drastically compared to its ancestors. Because sometimes, the best way to survive is to stay as similar as possible to the best versions of yourselves, such as the case for crocodiles, coelacanths, and horseshoe crabs. In other words, staying relatively stable is also an evolutionary strategy that could be successful.

Read next: People Wonder If Humans Could One Day Turn Into Fossil Fuels — Here’s What Scientists Think Would Happen