Sixty-six million years ago, a asteroid hit the earth with the force of 10 billion atomic bombs and changed the course of evolution.
the the sky darkened and the plants stopped photosynthesising. The plants died, then the animals that fed on them. The food chain collapsed. On 90 percent of all species Gone When the dust settled, everything dinosaurs except a bunch of birds it had been extinguished.
But this cataclysmic event made human evolution possible. Surviving mammals flourished, including small proto-primates that would become us.
Imagine if the asteroid had missed and the dinosaurs survived. Imagine highly evolved raptors planting their flag on Moon. Dinosaur scientists, discovering relativity, or discussing a hypothetical world in which, unbelievably, mammals took over the Earth.
This may sound like bad science fiction, but it addresses some deep philosophical questions about evolution. Is humanity here by chance, or is the evolution of smart tool users inevitable?
Brains, tools, language, and large social groups make us the dominant species on the planet. there are 8 billion Homo sapiens on seven continents. By weight there more human than all wild animals.
we have modified half of the earth’s land to feed us It could be argued that creatures like humans were forced to evolve.
In the 1980s, paleontologists dale russell proposed a thought experiment in which a carnivorous dinosaur evolved to become a clever tool user. This “dinosauroid” had a large brain with opposable thumbs and walked upright.
It’s not impossible, but it’s unlikely. An animal’s biology constrains the direction of its evolution. Your starting point limits your ending points.
If you drop out of college, you probably won’t be a neurosurgeon, lawyer, or NASA rocket scientist. But you could be an artist, actor or businessman. The paths we take in life open some doors and close others. That is also true in evolution.
Consider the size of the dinosaurs. From the Jurassic, sauropod dinosaurs, brontosaurus and relatives became giants of 30-50 tons up to 30 meters long, ten times the weight of an elephant and as long as a blue whale.
This happened in multiple groups, including DiplodocidsBrachiosauridae, Turiasauridae, Mamenchisauridae Y titanosaur.
This happened on different continents, at different times, and in different climates, from deserts to tropical jungles. But other dinosaurs that lived in these environments did not become supergiants.
The common thread that united these animals was that they were sauropods. Something about the anatomy of sauropods. lungshollow bones with a high strength-to-weight ratiometabolism or All of these things – unlocked its evolutionary potential. It allowed them to grow in a way that no land animal had ever done before, or has since.
Similarly, carnivorous dinosaurs repeatedly evolved huge thirty-foot, multi-ton predators. more than 100 million years, megalosaurs, allosaurids, carcharodontosaurus, neovenatorides, and finally tyrannosaurs evolved giant apex predators.
Dinosaurs did big bodies well. big brains Not that much. Dinosaurs showed a weak trend toward increasing brain size over time. Like the dinosaurs of the Jurassic allosaurus, stegosaurus, Y brachiosaurus had small brains.
At the end of the Cretaceous, 80 million years later, tyrannosaurs and the duckbills had developed larger brains. But despite its size, the t rex brain still weighed only 400 grams. A velociraptor brain weighed 15 grams. The average human brain weighs 1.3 kilograms.
Dinosaurs entered new niches over time. Small herbivores became more common, and birds diversified. Long-legged forms evolved later, suggesting an arms race between fast-legged predators and their prey.
Dinosaurs seem to have had increasingly complex social lives. they began to live in herds and evolved elaborate horns for fighting and display. However, dinosaurs mostly seem to repeat themselves, evolving as giant herbivores and small-brained carnivores.
There is little about 100 million years of dinosaur history to suggest that they would have done anything radically different had the asteroid not intervened. We’d probably still have those long-necked supergiant herbivores and huge tyrannosaur-like predators.
They may have developed slightly larger brains, but there is little evidence that they became geniuses. Nor is it likely that mammals have displaced them. Dinosaurs monopolized their environments until the end, when the asteroid hit.
Mammals, for their part, had different limitations. They never evolved as supergiant herbivores and carnivores. But repeatedly they developed big brains. Massive brains (as big or bigger than ours) evolved in orcas, sperm whales, baleen whales, elephants, leopard seals, and apes.
Today, some descendants of dinosaurs, birds such as crows and parrots, have complex brains. can use instruments, speak and count. But it is mammals like apes, elephants, and dolphins that have evolved the largest brains and most complex behaviors.
So did eliminating the dinosaurs guarantee that mammals would develop intelligence?
Well, maybe not.
Starting points can limit ending points, but they don’t guarantee them either. Steve Jobs, Bill Gates and Mark Zuckerberg they all dropped out of college. But if dropping out automatically made you a billionaire, everyone who dropped out of college would be rich. Even starting in the right place, you need opportunities and luck.
The evolutionary history of primates suggests that our evolution was anything but inevitable. In Africa, primates evolved into big-brained apes, and throughout 7 million yearsproduced modern humans. But elsewhere, primate evolution took very different paths.
When monkeys reached south america 35 million years ago they evolved into more species of monkeys. And primates made it to North America on at least three separate occasions, 55 million years ago, 50 million years agoY 20 million years ago.
However, they did not become a species that makes nuclear weapons and smartphones. Instead, for reasons we don’t understand, they went extinct.
In Africa, and only in Africa, primate evolution took a unique direction. Something about the fauna, flora or geography of Africa fueled the evolution of apes: terrestrial, corpulent, big brain, Tools use primates
Even with the demise of the dinosaurs, our evolution needed the right combination of chance and luck.
Nicholas R. LongrichAssociate Professor of Paleontology and Evolutionary Biology, bath university
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