Why Did Vertebrates Leave the Sea for the Land?

Our prehistoric aquatic ancestors didn’t simply decide one day to leave the water and live on land. The evolutionary process that led crocodile-like creatures to grow legs took millions of years. By studying fossils, researchers at Northwestern University have concluded that the process actually began with an increase in the size of those ancient animals’ eyes, hypothesizing that seeing prey on land kick-started the anatomical changes. The researchers found that the eyes of aquatic vertebrates nearly tripled in size before the water-to-land transition.

What big eyes you have:

  • “Why did we come up onto land 385 million years ago? We are the first to think that vision might have something to do with it,” said lead researcher Malcolm MacIver.
  • Their hypothesis centers around water dwellers “seeing an unexploited cornucopia of food on land,” which “drove evolution to come up with limbs from fins,” MacIver said.
  • The expanded visual range of seeing through air (instead of water) may have led to larger brains in early terrestrial vertebrates, and the ability to plan, rather than merely reacting, as fish do.
More Info: Northwestern University

Discussion Comments


Wow! Another theory? Will be waiting for someone to detail how the minor/major changes occurred in time for the "big eyed" creatures to take advantage of the "food" on shore. How did they "know" it was even food? And how did these creatures choose to voluntarily "change" their bodies? Would that we humans could do that today without our modern technology.

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