Coincidentally, in earlier England, a novel called Gulliver's Travels tells the story of the giant country. The people in the giant country are burly, more than 20 meters high, which is very scary. Of course, adults and giants are fictional artistic images, but from a biological point of view, nature has created all kinds of creatures. The largest African elephant on land weighs 10 ton, and the blue whale in the sea weighs 150 ton. Why didn't it create a monster like an elephant or a dinosaur? There is no intention to keep the suspense here for the simple reason. Because the laws of nature have strict restrictions on the size of all living things. All animals in nature have the right size. The change of animal body shape will inevitably lead to the change of body shape.

Take the legendary giant as an example. The height of giants is 10 times that of ordinary people. If his figure remains the same, his width and thickness will be 10 times that of ordinary people. So his own weight is 1000 times that of ordinary people, about 80 tons. However, the cross-sectional area of his skeleton is only 100 times that of ordinary people, so the load on the giant skeleton per square centimeter is only 10 times that of ordinary people. Under such a heavy load, the giant will break his leg if he takes one step. Therefore, it is not a great skill for ordinary people to defeat giants.

Gravity is a burden to people, and even more terrible to giants. Normal walking of giants can also cause bone damage or cerebral ischemia. They need high blood pressure and strong blood vessels, because they need to push blood to higher places. In other words, even if the giant didn't fall down because of a fracture, he would die because of a ruptured artery. Now, we humans have to evolve to a larger size at a very slow speed. Although there are few advantages, tall people have some advantages in all aspects of social life. If time is too long, human beings will grow bigger and bigger.

First of all, the so-called giants are at least people. If intelligence and morphology evolve into a species that is too different from ours, it will not work. This limits the upper limit. Imagine that. When humans walk upright, their upper weight limit is much smaller than that of other large animals. The largest dinosaur may have exceeded 90 tons, but the average adult Tyrannosaurus rex weighing 9 tons can't run. An elephant with an average weight of 5 tons can't jump any more. The circus's hind leg upright performance is a kind of torture for elephants. Animals whose hind legs account for nearly half of our height can't resist the persecution of gravity.