Basic stage

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Representative and main characteristics of fossil origin

Cultural development

Early ape-man

From 2 million years ago to 6.5438+0.75 million years ago, Homo habilis (Oduwe Gorge Valley, Tanzania) had a brain capacity of 637 ml and walked upright. His thumb and four other fingers can be clenched, but his movements are not accurate. Gravel can be made into a kitchen knife, and this stone culture is called Oduwe culture. Capable people live entirely by nature.

Late ape-man

1.75 million years ago to 200,000 ~ 300,000 years ago Yuanmou (Shangnabang Village, Yuanmou, Yunnan Province, China)

Beijingers (Zhoukoudian, Fangshan District, Beijing, China)

Javanese (West Java, Indonesia) has a brain capacity of 1 059 mL, can walk upright on two feet like modern people, and can build a variety of stone tools with flexible hands. Can make all kinds of stone tools, exquisite processing, stone culture has made great progress. It can live in groups of dozens of people with fire, and has certain ability to cope with natural changes.

Early homo sapiens

Maba people from 200,000 to 300,000 years ago (Maba Township, Qujiang County, Guangdong Province, China)

The brain capacity of Neanderthals (Neanderthal Valley, Germany) is 1 350 mL, which is close to that of modern people, and some primitive features (protruding mouth, developed eyebrows and ridges, etc.). ) is preserved in the constitution. Can make tools, can hunt large beasts, master artificial fire technology, and further improve the ability to conquer nature.

Late homo sapiens

Caveman from 50,000 years ago to/kloc-0,000 years ago (Zhoukoudian, Fangshan District, China)

The brain capacity of Kroma farmers (rural Kroma people) is basically the same as that of modern people, reaching 1 400 mL, and their posture is similar to that of modern people. Can make complex tools, such as stone tools, bones and horns, can make exquisite and unique works of art and decorations, can sew clothes, set up tents, and can carry out large-scale hunting activities. May start a matriarchal social life.

Two. There are too many stories about life on earth, and the most incredible story is about how we got our legs. Scientists believe that a long time ago, a fish landed on land, grew feet and began to walk. This is one of the most important events in the history of life-because that kind of fish is our ancestor. But how and why do fish have feet? For more than a century, even the best scientists have been unable to answer this question. They do have a guide, that is, the founder of evolution-Charles Darwin. Darwin said the answer was in that pile of rocks. Somewhere, you can find some fossils, which can explain everything. So paleontologists travel all over the world just to find them. Unfortunately, such ancient fossils are rare.

The story of quadrupeds

The longer scientists look for it, the more they realize that an important fossil is missing, which has become a big challenge to the whole theory of evolution. And the story about how we got our feet becomes the pursuit of "the ultimate lost fossil". As early as 150 years ago, this continuous pursuit began because of a simple observation: a large group of seemingly unrelated animals are actually related-they all have limbs, so they are collectively called quadrupeds.

Man is a quadruped because he has two hands and two feet. Cats, dogs and horses are obviously quadrupeds. In fact, all mammals are quadrupeds. Birds, frogs, lizards, even snakes without feet, and whales that seem to have no feet are also quadrupeds. All quadrupeds, no matter how different they look, have basically the same structure under the epidermis. Scientists are also puzzled by this fact. Dinosaurs have thorns, people have thorns, and quadrupeds have thorns; There is also the pelvic bone connecting the weight of the spine support; They all have breasts to protect their hearts and lungs. All quadrupeds breathe air through their nostrils. The top of their limbs is composed of a bone, and there are a pair of bones extending to their hands or feet below, which never seem to exceed five fingers or toes. Not only for dinosaurs and people, but also for whales. There are five fingers under the whale's flippers.

This similarity makes scientists believe that all quadrupeds must have come from a common ancestor. To prove this, they think only two kinds of fossils are needed. First of all, you need to walk on land, and it is a quadruped with five toes on each foot; Secondly, we need the fish with the earliest feet. It was this fish that became the first quadruped to walk ashore. Find the fossils of these two animals, compare them, find out their differences, and you can know why fish have feet.

There is an important clue that can guide scientists to explore, that is, this evolution probably happened in Devonian 400 million years ago. However, the Devonian period is so old that even the stones of that era are hard to find, let alone any fossils. But scientists know that before Devonian, there were no walking animals on land, but after Devonian, there were walking animals everywhere on land, so the evolution of limbs must have happened at that time.

Textbooks say that Devonian is really a hot and unbearable period, and almost no living things can survive on land, even plants are no exception. At that time, the land was really a barren and empty wilderness with no vitality. In other words, at that time, most creatures on the earth could only stay in the water. This is the age of fish, and one of the fossils, the earliest fish with feet, is the second fossil that scientists need to look for. It can be said that people are also fish, and it is precisely evolved from fish.

Did you find your ancestors?

It seems not difficult to find the fossil of that fish. By the end of19th century, scientists focused on a fish, that is, Devonian round fin.

The fin of the round fin has a unique bone structure, which seems to be the predecessor of human thighs and arms. In particular, one kind of round fin, the extinct palm fin fish, has leg bones, but lacks feet and toes. Therefore, scientists believe that this fish is the ancestor of all of us, and we have no ancestors with limbs.

At the beginning of the 20th century, some scholars put forward a theory to explain why this fish evolved legs and began to walk. That cruel Devonian sun must be the source of drought. Those fish that used to live freely were suddenly trapped in the increasingly dry pond and faced with death. In order to survive, some palm fin fish have to escape from puddles and look for deep water. So, just like the jumping fish now, the palm fin fish drags its fins and barely "walks" onto the land. Some began to evolve on land, fins became limbs, five fingers and five toes grew, and they began to walk.

In this way, they became quadrupeds and became our ancestors. They grow limbs because only in this way can they do what we all do: walk on land. The "pond dried up" theory seems to explain everything-why we grow limbs and what animals we evolved from. In order to prove this theory, we only need to find the earliest quadruped on the earth-the animal that evolved as soon as the fish landed, which is the first fossil mentioned above. If this animal has only five fingers and five toes, as scientists predict, then it is finished. To this end, many scientists have been trying to find this mysterious animal fossil for many years, but failed to find it.

If you want to see Devonian rocks exposed from the ground, you can only go to one of the few places in the world, one of which is Greenland. So in the 1930s, a group of Swedish scientists visited here many times, and their task was to find the first animal with legs. Among this group of experts, Eric Jarvik, who was taciturn and opinionated and disliked in the whole paleontology world, found what people dreamed of-the earliest animals with legs and feet (not fins). Jarvik called it ichthyosaur.

Since 1859 after Darwin, people have been looking for this significant animal, and now they have finally found it, which of course rejoices the whole paleontology community. What Jarvik has to do now is to reconstruct the anatomical structure of this strange animal as much as possible. Of course, all this will take a long time. Although Jarvik is an excellent anatomist, he started his work from 1948, but he didn't finish the basic analysis until 1996. During this period, he completed two papers, which confirmed the current theory. Jarvik said that ichthyosaur was indeed a quadruped that walked on land. It has five fingers and five toes. Thus, the mystery of why we have hands and feet has been solved: when the palm fin fish struggled to land with its fins, it evolved into the earliest quadruped-ichthyosaur. This is completely consistent with the scientists' prediction.

However, it was immediately pointed out that there was a big loophole in Jarvik's statement, and ichthyosaurs probably didn't evolve directly from palm fin fish, because the difference between them was too great. Fishbone is a fully formed quadruped, that is, it has a chest, a pelvis connected to the spine, and fingers and toes on its limbs. Palm fin fish is still a kind of fish. Although it has primitive leg bones, it does not show many other characteristics of evolution to quadrupeds. This means that an "intermediate animal" must be found, which can show that the transition from fish to quadruped did happen. Therefore, this "intermediate animal" should not only be able to walk, but also be an animal that is half like a fish and half like a quadruped. "Intermediate animal" is what Darwin called "transitional form". "Transitional forms" are the core of evolutionary theory, because they show that one animal can mutate into another. When the environmental conditions change dramatically, there will be a "transitional form" in the process of evolution. Animals that can't adapt to the new environment will become extinct, but accidental mutation is often the key to ensure their survival. As a group of eccentric mutant animals struggle to survive in the new environment, most of them will soon become extinct, and only a few will become "transitional animals", that is, "intermediate animals" half like old animals and half like new animals, while new animals will completely abandon their old lifestyles. Fossils in "transitional form" have thus become the most important fossils in the evolution of all species.

However, "transitional form" is also the rarest animal species. It is not difficult to see from their nature that they are not only few in number, but also live in a very short transitional period. When a brand-new animal evolves, the "transitional form" disappears completely. In fact, for many years, only one animal was considered as a "transitional form"-Archaeopteryx, which was considered by some scientists as a feathered dinosaur, marking the transition from dinosaur to bird. It is speculated that the "transitional form" will soon be replaced by its own, more developed offspring. This "transitional episode" is quite short in the evolutionary history of life, and the number of species participating in the transition and the number of individuals of each species seem to be relatively small.

The trouble is, if we can't find the "transitional form" between palm fin fish and fish stone fish, we can't fully explain why we grow legs and feet.

If science can't explain exactly how fish evolved into quadrupeds, creationists will make sense. A creationist who works as a museum curator in the west said: There are many more fossils now than in Darwin's time, right? There are nearly 257 different kinds of fossils in our museum alone. If the theory of evolution is correct, there must be some fossils of "intermediate animals", but why not? On the contrary, every animal seems to be shaped, with no ancestors and no "transitional form". On this basis, creationists insist that the world was created in six days according to God's will, and all animals were of course created by God, so the so-called "evolution" does not exist at all. Scientists also believe that although the number of "transitional forms" is small, the survival time is short, and the chances of becoming fossils are few, if even one such fossil can not be found, the challenge of creationism to science will continue. Therefore, paleontologists are determined to find a "transitional form" between fish and our earliest ancestors.