Why is there a big difference in human appearance and very little difference between animals of the

Although there are no actual measurements, just a closer look at a group of cats, dogs, horses, cows, etc., we can see that almost every individual, when they are straightened, has a higher degree of symmetry than humans on the left and right sides, despite the slight differences. For example, it's almost impossible to find a cat with a clear asymmetry between left and right.

When we observe actual human beings, or human beings (except celebrities) in newspapers, magazines, television, and the Internet, we will find that for most people, even if the body is straightened, whether it is the face or other parts of the body, the left and right sides are generally obviously asymmetrical. Of course, there are people with a high degree of symmetry, but they are not in the majority.

When we look at a group of cats and other animals, we will also find that the similarity in appearance (only considering the outline, not the color) between different individuals of the same group of cats is very high, and there are very few that look particularly ugly. On the other hand, human beings have a lot of differences in appearance between different individuals, including those who are particularly regular and beautiful, those who are average-looking, and those who are very asymmetrical and ugly.

How can this be explained? There could be a number of reasons for this. For example, racial mixing may be one of the reasons for the phenomenon of (2) (discreteness) above.

But point (1) (asymmetry) is difficult to explain by racial mixing. The main thing I want to discuss in this article is another interpretation, which is evolution.

Interpretation. We know that the evolutionary process is roughly composed of two parts, namely "random variation" and "directional selection". Variation is random and not directional, whereas natural selection is directional.

1. External factors. Diets and lifestyle habits vary greatly between people, but not among animals. Especially in human captivity, the diet is basically completely homogeneous. Wild animals.

The living conditions are strange, and if you are often hungry and full, the difference in body size will be greater. But how can this "difference" be measured? In the case of variance, it may be difficult to obtain data on wild animals, so it is difficult to say whether there is a big difference in human or animal size.

2. Internal factors. The genetic diversity of humans is very large, compared to the genetic diversity of animals selected by humans, because only stable inheritance can obtain a fixed breed. For example, white-feathered chickens that have been selected and bred for many generations.

It's almost the same. But-

3. Questions about the problem. What are the boundaries of species? The scientific community does not yet have a particularly precise definition, and reproductive isolation is generally regarded as one of the hard criteria for species distinction.

If you look at it this way, there is no reproductive isolation between the various subspecies of dogs, so they are all the same species, but the size difference between different dogs is probably greater than that of people, think of Tibetan mastiffs and Chihuahuas.

Because the number of human genes is very huge, it is much more than some other animals, and they do not have some specific genes between animals, so there is no way to make a big difference.

Because the living environment of human beings in different regions is changeable, and the living environment of animals is single, and the places where humans live are cold in some places and hot in some places, the direction of evolution is different, so the difference will be great.

I don't think it's that the difference in appearance between animals is too small, but because we generally don't care about the details of animals, some are covered by fur, some are covered by skin color, and if you look closely, in addition to the overall outline, many others are different.

Because we are human, we are more sensitive to differences between people and less sensitive to differences between animals.

Because human genes are diverse, while animals are not genetically diverse. So everyone looks different.

In fact, animals all look exactly the same, but they are actually different, and the same is true for humans, what they see in their eyes is the same, and we may look different because of the difference in the structure of our eyes.

It's different kinds of people, bones and flesh are different, the shape of the bones is much worse, and some people will have fewer bones, and the performance is not the same.

Animals look absolutely different, if you have a group of livestock at home, raising dozens of hundreds of cows, you see for yourself, in addition to the difference in color, each of their cows has great differences in eyes, ears, nose, and even nose, they are not cloned, they are definitely different,It's just that we humans don't look closely, even if they all look the same, aren't they all cows?

These animals are generally distinguished by their ears and noses, because each animal has some differences in taste.

Animals often distinguish each other by their own language and by their specific smells.

They identify each other by smelling their smells. Many animals socialize through their sense of smell.

Due to the size of the human body and the habit of walking upright, the differences between human appearances are much greater than those of the same species. Because of the size of the body and the habit of walking upright, the differences between people are magnified.

We can assume that in such a scene, with a railing as the boundary, behind the railing is a horse standing, and in front of the railing stands a baby goat, do you think that the appearance of the two is very different? The answer is yes. Little goats and big horses may have a lot of similarities in some aspects of appearance, but because the size difference between the two is too big, people automatically ignore these similarities when they compare, which leads to people always intuitively feeling that the difference between the two is very large.

In the same way, because the size of human beings is generally larger than that of animals, we may not find many differences in small things, but we can find many differences in large things. That's why we find a lot of differences in two very different people. For example, the height of a human being can make the difference between two people very large, but these heights fall within the normal range of human beings.

The reason why human beings look very different in appearance has a lot to do with people walking upright. Walking upright will make people see the person's appearance more intuitively, so the difference between two people will be obvious. In the animal kingdom, which is generally on all fours, they don't often walk upright without training, so it's difficult to discern the differences between two animals of the same kind.

It is precisely because of the influence of human body size, coupled with the habit of walking upright that human beings have developed to walk, which makes the differences between people gradually magnified. As animals of the same kind, their small size, coupled with their habit of moving on all fours, cleverly conceals the difference between them. That's why human beings are always more different in appearance than animals of the same species.

Because genes are different. Animals reproduce in the same type, while humans are more advanced and reproduce through genetic inheritance, so there are big differences.

The races of the same animals are almost the same, and in the eyes of animals, they are actually different, and humans look different because humans know more about themselves.

Because human genes are strong, human genes are strong, so they can combine different appearances.