Anyone surprised by recent news of orcas attacking boats might be relieved to know that scientists have determined these massive mammals have evolved to the point where they can never migrate back to land. The same applies to all whales and dolphins, and, in fact, all "fully aquatic" mammals, reports Live Science, citing a study in the Proceedings of the Royal Society B. The unusual hypothetical requires a big-picture backdrop: The first life began in the oceans, and the first creatures crawled out of the ocean onto land between 350 million and 400 million years ago, per Phys.org. About 100 million years later, some of those land creatures ventured back into the sea and eventually "evolved the means to live there."
For this study, researchers looked into whether they might evolve back into land animals and concluded the answer is no—at least for those that are now in the "fully aquatic" camp, such as whales, per a post at Interesting Engineering. It seems they "passed an evolutionary threshold that marks the point of no return to terrestrial life," as Live Science puts it. One factor: Generally speaking, when land animals went back into the sea, they grew much larger, the better to retain heat in the cold depths of the ocean. This isn't a new idea—Belgian paleontologist Louis Dollo theorized in the 19th century that evolution probably doesn't do take-backs, stating that once an animal line loses a complex trait, like walking on land, it's probably not coming back. (More discoveries stories.)
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