Evolution takes some weird twists and turns to bring animals to their current forms. While evolution is based on random mutations and passing on traits that aid in survival, that does not mean that a particular animal will always be able to adapt to its changing environment.

For example, sometime around 350-400 million years ago, multiple different types of fish found their way out of the water and onto land. From here, they evolved into mammals, reptiles, and amphibians. Then, oddly enough, around 250 million years ago, some of them apparently changed their minds and moved back into the water to become animals like whales and penguins.

So, would it be possible now for a whale, for example, to evolve in such a way that it can once again survive on land? According to a 2023 study done by researchers in Switzerland and Sweden, it may be possible, but it is extraordinarily unlikely.

The team looked at more than 5600 different mammal species to see if their aquatic adaptations are irreversible. They started this by dividing the animals into four groups:

• No Aquatic Adaptations – These are animals that live fully on land, like dogs, cats, elephants, etc.
• Some Aquatic Adaptations with Mobility on Land – These are mammals that have some aquatic adaptations but are still able to move around on land.
• Some Aquatic Adaptations with Limited Mobility on Land – These are mammals that live primarily in the water but can still survive and move on land, though in limited ways.
• Fully Aquatic Mammals – These are mammals that cannot survive on land and would include animals like whales and dolphins.

They looked at these animals and modeled various evolutionary trees to see how different traits evolved over time so that they could estimate how likely it would be for specific traits to emerge.

What they found was that once an animal hits a certain point in its evolution from semi-aquatic to fully aquatic, they cannot return. This is because the traits that have to evolve require complex adjustments, including the ability to retain body heat in the water, increases in size, and a shift toward primarily carnivorous diets.

So, while mammals that have evolved to be fully aquatic are able to thrive in their environments, they are highly unlikely to ever evolve in such a way that would allow them to someday return to land.

Of course, while it is improbable that this would ever happen, evolution does some crazy things, so it can’t be 100% ruled out.

If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?