66 million years ago, an asteroid hit Earth with the power of 10 billion atomic bombs, an event that completely changed the course of evolution.
The sky was dull and the plants stopped photosynthesis. Plants die, and then the animals that feed on plants also go to extinction. The food chain on Earth has completely collapsed. More than 90% of species have disappeared. When the dust settled, all but a few birds were extinct.
However, this catastrophic event made human evolution possible. The surviving mammals began to flourish, including those that would later evolve into our small proto-mammals.
But imagine if the asteroid hadn't hit Earth, and if the dinosaurs had survived. Imagine again that highly evolved birds of prey planted small flags on the surface of the moon; Dinosaur genius scientists proposed the theory of relativity; Or maybe dinosaur evolutionists are discussing a hypothetical world in which mammals actually take over the planet!
This may sound like bad science fiction, but at its core, there are some profound philosophical questions about evolution: Is the existence of humans accidental, or is the evolution of species that use intelligent tools inevitable?
The evolution of dinosaurs
Brains, tools, language, and large social groups make us the dominant species on Earth. On all seven continents of the world, about 8 billion Homo sapiens live. By weight, humans are heavier than all wild animals combined. We have transformed half of the planet to feed ourselves. You can think that the evolution of creatures like humans is predestined.
In the '80s, paleontologist Dale Russell proposed a thought experiment in which a carnivorous dinosaur evolved into a user of intelligent tools. This "dinosaur man" has a large head, a pair of thumbs, and can walk upright.
This is not entirely impossible, but it is unlikely. The evolutionary direction of an animal is governed by its biological characteristics, in other words, your starting point limits your end. For example, if you drop out of college, you may not be able to become a brain surgeon, lawyer, or astronomer. However, you still have the opportunity to become an artist, actor or entrepreneur. The paths of life open some doors for us and close others, as does evolution.
Giant dinosaurs and mammals. (Photo: Nick Longrich)
Let's talk about the size of the dinosaur. From the Jurassic onwards, sauropods, pterosaurs and similar dinosaurs evolved into behemoths weighing 30-50 tons, up to 30 meters long, 10 times the weight of elephants, and as long as blue whales. This occurred in several groups, including Diplodocus, Brachiosaurus, Turiaosaurus, Mamenxiosaurus, and Titanosaurus. It also occurs on different continents, at different times and in different climatic conditions, from deserts to rainforests. However, some other dinosaurs that also lived in these environments did not become superbeasts.
What these animals have in common is that they are all sauropods. Some of the anatomical features of sauropods, including lungs, hollow bones with a high strength-to-weight ratio, metabolism, or all of them, unleashed their evolutionary potential to grow larger in a way that was "unprecedented among land animals."
Similarly, carnivorous dinosaurs have repeatedly evolved into giant predators that are ten meters long and weigh several tons. Over 100 million years, Spotted Dragon, Allosaurus, Squalosaurus, New Hunters, and finally Tyrannosaurus evolved into giant apex predators.
The ratio of brain to body mass in dinosaurs, mammals, and birds. (Photo: Nick Longrich)
The huge bodies of dinosaurs evolved well, but the brain is another matter. Dinosaurs did show a faint trend, with their brains enlarging slightly over time. Jurassic dinosaurs such as Psomyosaurus, Stegosaurus and Brachiosaurus had small brains. By the late Cretaceous, about 80 million years later, Tyrannosaurus and platypus had evolved larger brains. However, despite its larger size, the brain of Tyrannosaurus rex weighed only 400 grams. The brain of a velociraptor weighs about 15 grams. For comparison, the average weight of a human brain is 1.3 kg.
Over time, dinosaurs entered new ecological niches. Small plant-eating dinosaurs are more common, and birds are more diverse. The long-legged form was later evolved, suggesting that an arms race took place between predators and prey "walking like a fly".
Dinosaurs seem to have emerged with increasingly complex social lives. They began to live a gregarious life and evolved elaborate horns for fighting and display. However, dinosaurs seem to have mostly repeated themselves, with giant plant eaters and carnivores with tiny brains appearing.
Without the "intervention" of asteroids, 100 million years of dinosaur history shows little that they would have fundamentally changed. It is likely that they will still be those long-necked super-giant plant eaters and huge tyrannosaurus-like carnivores. They may have evolved slightly larger brains, but there's little evidence that they evolved into "geniuses."
Mammals, meanwhile, have different limitations. They never evolved those super-giant plant and carnivores, but they evolved brains over and over again. Killer whales, sperm whales, baleen whales, elephants, leopard seals, and apes have all evolved huge brains, some as big as we are, or even larger.
Today, the very few descendants of dinosaurs, birds like crows and parrots, also have relatively complex brains. They know how to use tools, talk and count. But mammals like apes, elephants and dolphins evolved the largest brains and the most complex behaviors.
Is this inevitable?
So, did the extinction of dinosaurs guarantee that mammals evolved intelligence? Perhaps this is not the case either.
The starting point may limit the end, but it also does not guarantee where to go. Steve Jobs, Bill Gates, and Mark Zuckerberg all dropped out of college, but dropping out is not a condition for making one a billionaire "automatically." Even if you start right, it takes chance and luck.
The evolutionary history of primates shows that our evolution was not inevitable. In Africa, primates did evolve great apes with large heads, giving birth to modern humans over a period of 7 million years. But there are other places where primates have evolved down very different paths.
Lion-tamarin, a South American monkey. (Photo: Wikimedia Commons)
When monkeys arrived in South America 35 million years ago, they simply evolved a richer monkey species. Primates have set foot in North America at least three times, 55 million years ago, 50 million years ago and 20 million years ago. However, they have not evolved a species that can make smartphones, but have gone extinct for reasons we don't yet understand.
In Africa, and only in Africa, primate evolution has taken a unique direction. Factors related to the flora and fauna of Africa or the geographical environment drove the development of great apes, which became terrestrial, large, large-headed, tool-wielding primates.
That is, even if the dinosaurs disappeared, our evolution would require chance, plus some luck.
Nicholas Longrich (Senior Lecturer in Paleontology and Evolutionary Biology, University of Bath)
Compiled by Takeko
Original link:
https://theconversation.com/what-if-the-dinosaurs-hadnt-gone-extinct-why-our-world-might-look-very-different-191599
首图：Nick Longrich, Wikimedia Commons, CC BY-SA