What Would Evolution Look Like If Dinosaurs Hadn’t Gone Extinct?


One fateful day when an asteroid hit the Earth sixty-six million years ago, it extinct nearly all living species, leaving only a few species of birds. But what if that defining moment had never happened? If dinosaurs had persisted to live to this day, what would the world look like, and would mammals have grown into intelligent human beings?

It is difficult to visualize highly intelligent raptors and triceratops creating the lightbulb, becoming CEOs, or creating political and social societies.

However, the hypothetical scenario in which dinosaurs didn’t go extinct forces us to take a philosophical look at evolution – are humans here by dumb luck, or is the evolution of intelligent beings inevitable?

To answer this question, let’s first explore whether dinosaurs could have evolved into a high-thinking species. In the 1980s, paleontologist Dale Russell envisioned a scenario in which a carnivorous dinosaur became intelligent with a big brain, opposable thumbs, and could walk upright.

This “dinosauroid” is not inconceivable but it is unlikely due to the biology of dinosaurs. Most notably, an animal’s starting point determines its evolutionary endpoint. This phenomenon is apparent in how dinosaurs’ bodies and brains evolved during their time on Earth.

Beginning in the Jurassic Period, sauropod dinosaurs, Brontosaurus grew to be 33–55 tons and nearly 100 feet in length. This evolution occurred in multiple dinosaur groups during different time periods on different continents with a wide variety of climates. But other groups in these same areas didn’t become supergiants.

The giant dinosaurs were all sauropods, and the theory is that parts of the sauropod anatomy – lungs, hollow bones with a high strength-to-weight ratio, metabolism, or a combination of features – enabled them to evolve into the largest land animals ever.

While dinosaurs successfully evolved in body size, Jurassic groups like Allosaurus, Stegosaurus, and Brachiosaurus, had small brains. There are notable exceptions. By the late Cretaceous Period, tyrannosaurs and duckbills evolved larger brains, and some dinosaurs further adapted by becoming smaller, growing longer legs, and interacting strategically in social situations.

Despite these gains, the brains of evolving giant herbivores and carnivores remained small, suggesting that given millions more years on Earth, dinosaurs would probably never have become intellectual beings. And given their enormous size, mammals would likely never have displaced them.

On the other end of the spectrum, evolving mammals were constrained by their smaller size. However, mammals’ brains grew bigger with time, suggesting that the extinction of dinosaurs guaranteed that mammals would develop intelligence and dominance. But alas, primate evolutionary history is not that simple.

Primates in Africa did progress into big-brained apes and over a period of 7 million years, became modern humans. But primates in other parts of the world evolved differently. The monkeys that reached South America 35 million years ago just evolved into more monkey species. Three separate primate groups in North America eventually went extinct.

What about Africa – flora, fauna, geography, climate – allowed humans to flourish there? Despite extensive research, a definitive answer continues to evade us. As unsatisfying as it may be, evidence indicates that once all dinosaurs disappeared, human evolution was a product of luck and chance.

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