Sixty-six million years ago, an asteroid hit the earth with the force of 10 billion atomic bombs and changed the course of evolution.
The clouds darkened and the plants stopped photosynthesizing. The plants died, then the animals that ate them. The food fell. More than 90 percent of all living things became extinct. When the dust settled, theall the dinosaurs except a few birds were extinct.
But this terrible event made human evolution possible. The remaining mammals evolved, including small animals that evolved into living creatures.
Imagine that the asteroid missed, and the dinosaurs survived. Imagine highly evolved raptors planting their flag on the Moon. Dinosaur scientists, finding a relationship, or discussing a fictional world where, mysteriously, mammals took over the Earth.
This may sound like science fiction, but it gets to deep, philosophical questions about evolution. Did humanity just exist by accident, or is the evolution of intelligent users inevitable?
Brains, tools, languages and large social groups make us the largest species on earth. There are 8 billion A wise man on seven continents. By weight, there are more humans than all wild animals.
We have changed half the world to feed ourselves. You can argue that creatures like humans change.
In the 1980s, paleontologist Dale Russell suggested that the carnivorous dinosaur evolved into an intelligent tool-wielding human. This “dinosauroid” had a large brain and large toes that were opposed to vertical movement.
It’s not impossible but it’s impossible. Animal biology limits its evolution. Your starting point determines your ending point.
When you leave college, you probably won’t be a brain surgeon, a lawyer, or a NASA rocket scientist. But you can be an artist, an actor, or an entrepreneur. The paths we take in life open some doors and close others. It is the same with evolution.
Consider the size of the dinosaurs. Beginning in the Jurassic, the sauropod dinosaurs, Brontosaurus and relatives turned into giants 30-50 tonne 30 meters long – ten times the weight of an elephant and the length of a blue whale.
This happened in several groups, including Diplodocidae, Brachiosauridae, Turiasauridae, Mamenchisauridae and Titanosauria.
This happened on different continents, at different times and in different places, from deserts to rainforests. But the other dinosaurs that lived in these places were not very big.
What unites these animals were the so-called sauropods. Something about their body structure – lungs, bare bones with a power-to-weight ratio, metabolism, or all of these things – unlocked their evolutionary potential. It allowed them to grow in a way that wild animals never had before, or since.
Similarly, the carnivorous dinosaurs repeatedly evolved into large, ten-meter-tall, several-ton beasts. Over 100 million years, megalosaurids, allosaurids, carcharodontosaurids, neovenatorids, and finally tyrannosaurs evolved into the largest predators.
Dinosaurs did big bodies well. Big brain not so much. Dinosaurs showed slow brain development over time. Jurassic dinosaurs love it Allosaurus, stegosaurus, and Brachiosaurus he had a small brain.
By the end of the Cretaceous, 80 million years later, tyrannosaurs and duckbills had evolved large brains. But despite its size, it is T. rex the brain still weighed only 400 grams. A Velociraptor the brain weighed 15 grams. The average human brain weighs 1.3 kilograms.
Dinosaurs moved into new areas over time. Small herbivores became more common and birds became more diverse. The long-legged form evolved later, implying a competition for weapons between terrestrial animals and carnivores.
Dinosaurs seem to have had a very tough life. They began to live in herds and changed the top horns to fight and display. Yet dinosaurs often appear to have replicated themselves, replacing large herbivores with small-brained animals.
There is little in the nearly 100 million years of dinosaur history to suggest that they would have done anything very different if the asteroid hadn’t intervened. We would still have very large animals, with long necks, and large animals like tyrannosaurs.
They may have evolved a slightly larger brain, but there is little evidence that they would have been smarter. There is also no doubt that mammals would have driven them from their homes. Dinosaurs ruled their land until it ended, when an asteroid hit.
Mammals, meanwhile, had different obstacles. They have not changed the larger animals of herbivores and carnivores. But again and again he changed the big brain. Large brains (as big or larger than ours) have come from orcas, sperm whales, baleen whales, elephants, leopard seals, and monkeys.
Today, a few dinosaur descendants – birds such as crows and parrots – have complex brains. They can use tools, speak and read. But it is mammals like monkeys, elephants, and dolphins that have evolved the largest brains and the most complex behaviors.
So did the removal of the dinosaurs guarantee that animals will change their minds?
Well, maybe not.
Preliminaries can limit conclusions, but they do not guarantee them. Steve Jobs, Bill Gates, and Mark Zuckerberg all dropped out of college. But if dropping out of school can make you a billionaire, every dropout can be rich. Even starting from the right place, you need luck and luck.
The evolutionary history of primates shows that our evolution was inevitable. In Africa, chimpanzees evolved into great apes and, over 7 million years, gave rise to modern humans. But elsewhere the evolution of primates took very different paths.
When chimpanzees arrived in South America 35 million years ago, they evolved into many species of chimpanzees. And primates arrived in North America at least three times, 55 million years ago, 50 million years ago, and 20 million years ago.
However, they have not turned into a brand that makes nuclear weapons and cell phones. Instead, for reasons we do not understand, it ended.
In Africa, and only in Africa, the evolution of primates took a unique course. Something about the fauna, flora or landscape of Africa triggered the evolution of primates: terrestrial, large-bodied, large-brained, tool-using primates.
Even after the dinosaurs were gone, our evolution required the right combination of luck and chance.
Nicholas R. LongrichSenior Lecturer in Paleontology and Evolutionary Biology, University of Bath
This article is reprinted from The Conversation under a Creative Commons license. Read the first article.
