Sixty-six million years in the past, an asteroid hit the Earth with the power of 10 billion atomic bombs and altered the course of evolution. The skies darkened and crops stopped photosynthesizing. The crops died, then the animals that consumed them. The meals chain collapsed. Over 90 p.c of all species vanished. When the mud settled, all dinosaurs besides a handful of birds had gone extinct.

However this catastrophic occasion made human evolution potential. The surviving mammals flourished, together with little proto-primates that may evolve into us.

Think about the asteroid had missed, and dinosaurs survived. Image highly-evolved raptors planting their flag on the moon. Dinosaur scientists, discovering relativity, or discussing a hypothetical world during which, extremely, mammals took over the Earth.

This would possibly sound like unhealthy science fiction, nevertheless it will get at some deep philosophical questions on evolution. Is humanity simply right here by probability, or is the evolution of clever tool-users inevitable?

Brains, instruments, language, and large social teams make us the planet’s dominant species. There are eight billion Homo sapiens on seven continents. By weight, there are extra people than all wild animals.

We’ve modified half of Earth’s land to feed ourselves. You possibly can argue creatures like people have been sure to evolve.

Within the Nineteen Eighties, palaeontologist Dale Russell proposed a thought experiment during which a carnivorous dinosaur advanced into an clever instrument consumer. This “dinosauroid” was big-brained with opposable thumbs and walked upright.

It’s not inconceivable nevertheless it’s unlikely. The biology of an animal constrains the path of its evolution. Your start line limits your endpoints.

If you happen to drop out of faculty, you most likely gained’t be a mind surgeon, lawyer, or Nasa rocket scientist. However you is perhaps an artist, actor, or entrepreneur. The paths we absorb life open some doorways and shut others. That’s additionally true in evolution.

Large dinosaurs and mammals via time. Credit score: Nick Longrich

Contemplate the scale of dinosaurs. Starting within the Jurassic, sauropod dinosaurs, Brontosaurus, and kin advanced into 30-50 ton giants as much as 30 meters lengthy—ten instances the burden of an elephant and so long as a blue whale. This occurred in a number of teams, together with Diplodocidae, Brachiosauridae, Turiasauridae, Mamenchisauridae, and Titanosauria.

This occurred on totally different continents, at totally different instances, and in numerous climates, from deserts to rainforests. However different dinosaurs residing in these environments didn’t develop into supergiants.

The widespread thread linking these animals was that they have been sauropods. One thing about sauropod anatomy—lungs, hole bones with a excessive strength-to-weight ratio, metabolism, or all these items—unlocked their evolutionary potential. It allow them to develop huge in a method that no land animals had ever earlier than, or have since.

Likewise, the carnivorous dinosaurs repeatedly advanced enormous, ten-meter, multi-ton predators. Over 100 million years, megalosaurids, allosaurids, carcharodontosaurids, neovenatorids, and eventually tyrannosaurs advanced big apex predators.

Mind measurement versus physique mass for dinosaurs, mammals, and birds. Credit score: Nick Longrich

Dinosaurs did huge our bodies nicely. Huge brains not a lot. Dinosaurs did present a weak development in direction of elevated mind measurement over time. Jurassic dinosaurs like Allosaurus, Stegosaurus, and Brachiosaurus had small brains.

By the late Cretaceous, 80 million years later, tyrannosaurs and duckbills had advanced bigger brains. However regardless of its measurement, the T. rex mind nonetheless weighed simply 400 grams. A Velociraptor mind weighed 15 grams. The typical human mind weighs 1.3 kilograms.

Dinosaurs did enter new niches over time. Small herbivores turned extra widespread and birds diversified. Lengthy-legged varieties advanced in a while, suggesting an arms race between fleet-footed predators and their prey.

Dinosaurs appear to have had more and more advanced social lives. They began residing in herds and advanced elaborate horns for preventing and show. But dinosaurs principally appear to repeat themselves, evolving big herbivores and carnivores with small brains.

There’s little about 100 million years of dinosaur historical past to trace they’d have carried out something radically totally different if the asteroid hadn’t intervened. We’d doubtless nonetheless have these supergiant, long-necked herbivores and big tyrannosaur-like predators.

They could have advanced barely greater brains, however there’s little proof they’d have advanced into geniuses. Neither is it doubtless that mammals would have displaced them. Dinosaurs monopolized their environments to the very finish, when the asteroid hit.

Mammals, in the meantime, had totally different constraints. They by no means advanced supergiant herbivores and carnivores. However they repeatedly advanced huge brains. Huge brains (as giant or bigger than ours) advanced in orcas, sperm whales, baleen whales, elephants, leopard seals, and apes.

At present, just a few dinosaur descendants—birds like crows and parrots—have advanced brains. They’ll use instruments, speak, and rely. Nevertheless it’s mammals like apes, elephants, and dolphins that advanced the most important brains and most advanced behaviors.

So did eliminating the dinosaurs assure mammals would evolve intelligence?

Nicely, perhaps not.

Beginning factors could restrict endpoints, however they don’t assure them both. Steve Jobs, Invoice Gates, and Mark Zuckerberg all dropped out of faculty. But when dropping out routinely made you a multibillionaire, each faculty dropout could be wealthy. Even beginning in the correct place, you want alternatives and luck.

The evolutionary historical past of primates suggests our evolution was something however inevitable. In Africa, primates did evolve into big-brained apes and, over 7 million years, produced trendy people. However elsewhere primate evolution took very totally different paths.

When monkeys reached South America 35 million years in the past, they only advanced into extra monkey species. And primates reached North America not less than three separate instances, 55 million years in the past, 50 million years in the past, and 20 million years in the past. But they didn’t evolve right into a species who make nuclear weapons and smartphones. As an alternative, for causes we don’t perceive, they went extinct.

In Africa, and Africa alone, primate evolution took a singular path. One thing about Africa’s fauna, flora, or geography drove the evolution of apes: terrestrial, big-bodied, big-brained, tool-using primates. Even with the dinosaurs gone, our evolution wanted the correct mixture of alternative and luck.The Conversation

This text is republished from The Dialog beneath a Artistic Commons license. Learn the authentic article.

Picture Credit score: Enrique from Pixabay

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