An asteroid hit the Earth with the force of 10 billion bombs, changing the course of evolution.
Plants stopped photosynthesizing when the skies turned dark. Animals fed on the dead plants. There was a collapse in the food chain. Most of the species disappeared. Dinosaurs were extinct when the dust settled.
Human evolution was possible because of this event. There were mammals that would evolve into us.
Dinosaurs survived the asteroid miss. Birds planting a flag on the moon. A hypothetical world in which mammals took over the Earth is one of the topics being discussed.
This might seem like a bad science fiction, but it has some deep questions about evolution. Is the evolution of intelligent tool- users inevitable or just happenstance?
The planet's dominant species is made up of brains, tools, language and social groups. On seven continents, there are 8 billion humans. Humans are more abundant than wild animals.
Half of Earth's land has been modified to give us food. Humans were bound to evolve.
Dale Russell proposed an experiment in which a dinosaur evolved into a tool user. The dinosauroid had opposable thumbs and was big-brained.
It's possible but not certain. The direction of an animal's evolution is dictated by its biology. It limits your endpoints.
You won't be a rocket scientist if you drop out of college. You could be an artist, actor, orentrepreneur. Some doors are opened and some are closed by the paths we take. It's true in evolution as well.
Take the size of dinosaurs into account. Ten times the weight of an elephant and five times the weight of a blue whale, the sauropod dinosaurs evolved into 30 meter giants.
This happened in a number of groups.
At different times, on different continents, and in different climates. Other dinosaurs that lived in these environments did not become supergiants.
The animals were linked because they were sauropods. The evolutionary potential of sauropods was unlocked by their lungs, hollow bones, and metabolism. They were able to grow big in a way that no land animals had before.
The dinosaurs had huge, ten-meter, multi-tonne predatory animals. The giant apex predator evolved over 100 million years ago.
Dinosaurs were able to build large bodies. Big brains aren't that important. Dinosaurs showed a weak trend towards larger brains over time. Dinosaurs had small brains.
The tyrannosaurs and duckbills had larger brains by the late Cretaceous period. The T.rex brain weighed 400 grams. The brain of a velociraptor was 15 grams. A human's brain is 1.3 kilograms in weight.
Over time, dinosaurs entered new niches. Birds diversified and become more common. The evolution of long-legged forms suggested an arms race between predator and prey.
Dinosaurs seem to have had a lot of different social lives. They developed elaborate horns for fighting and display. Dinosaurs are evolving with small brains.
If the asteroid hadn't struck, the dinosaurs would have done nothing differently. We'd probably still have giant, long-necked herbivores and tyrannosaurs.
There isn't much evidence that they would have evolved into geniuses. It's not likely that mammals would have moved them. Dinosaurs monopolised their environments.
Different constraints existed for mammals. They didn't evolve supergiants or carnivores. Big brains are the result of repeated evolution. Chimpanzees, orcas, sperm whales, baleen whales, elephants, leopard seals, and apes have massive brains.
Birds with complex brains are descendants of dinosaurs. They are capable of using tools, talking and counting. Animals like apes, elephants, and dolphins have the biggest brains and most complex behaviors.
The elimination of the dinosaurs might have guaranteed that mammals would evolve intelligence.
Endpoints can be limited, but starting points don't guarantee them. Bill Gates dropped out of college. College dropouts would be rich if they dropped out. You need opportunities and luck to get started.
Our evolution is thought to be anything but inevitable. Modern humans were produced over 7 million years ago in Africa as a result of primate evolution. There were very different paths taken by primate evolution.
35 million years ago, when monkeys first arrived in South America, they evolved into more primate species. At least three separate times, primate reached North America.
They did not evolve into a species that makes nuclear weapons or phones. They went extinct for reasons we don't comprehend.
primate evolution took a different path in Africa. The evolution of apes was driven by something about Africa's fauna, flora or geography.
Our evolution needed the right combination of chance and luck.
Nicholas R. Longrich is a senior lecturer at the University of Bath.
Under a Creative Commons license, this article is re-posted. The original article is worth a read.