7 months, 1 week ago
When animals evolve, it is very obvious if they can be less and not long, and what organs will shrink and then degenerate in a short period of time. As for why the head can't grow longer, let's first look at the need for the head to have two long. Telling the truth, if you directly bring the benefits of the two heads that you think are long, this answer is much easier. Regardless of the original animal or the back mouth animal, the first organ on the head is the mouth (in fact, there is a head after the mouth, all animals need to eat, but animals that need to exercise can have a head, even if it is not referred to as an organ, "head" At least it is also the title of a sport), is it necessary to have a long mouth? Whether it's filtering or preying, a big mouth is stronger than two small mouths, either with a larger open area or a stronger bite. No animal will need two small mouths instead of one big mouth. We know that animals are heterotrophic, and nothing can be done, but the body cavity of the digestive tract must be there. Go in the mouth, digest and absorb in the middle, and then the anus drains the residue, but the entrance to the real body cavity needs to be split into two? Of course, it is not ruled out that some of the lower animals that have (or have had) fixed filter foods have opened two or more entrances to their body cavity, but most animals do not have such an operation, and one mouth cannot reach that. Just use the limbs to send to the mouth, open two mouths, no. Then there are eyes, ears, noses, and these detector tubes. Is it necessary to have more sets of one head on the other? There is no need, it is enough to grow a head, and how long a head can avoid a dead angle. Finally, is there a need for two brains? Why do the brains need to be on the head? Personally, the original animals are not myelinated than the later advanced vertebrates. At that time, the nerve conduction is slow, and the animal's head is the front part of the movement, spreads all kinds of sensing organs, and is related to the most. The important food, the nerves are also the most dense, so the brain is naturally produced in the head, so that receiving key information is faster, and the response is faster. The brain is also two small and not as big as a big one, let alone two independent big ones. One plus one is less than two. Now these two opinions are different, and it is even more troublesome. So even if for some reason some animals have two mouths, it is a big head with a nose and a head and a small head with only one mouth. It is impossible to have two symmetrical heads. An animal can only have one direction of movement and one decision brain. If you want to say how long the benefits can be spared, this is not true. In fact, the evolution of biology has always been very cruel. It has never been more than a set of organs for the luxury of trauma. It is good to simply grow a system and live to breed. The eyes and ears are all dead. Not enough to grow up two (except the kidney, do not understand that the hairy fish is a kidney to the amphibious class becomes two independent, and I look forward to the explanation of the big sputum, the lungs and other respiratory systems seem to be symmetrical, but it was only one year The amphibious body flattened and squeezed the gradual evolution of the lungs to the sides of the chest. At least the ancestors were not enough. It is better to save the energy to grow these backups, and then live a lot of reproduction, and back up a single individual to be more secure. (ps: the left and right brain, named as left and right only, is originally one, and can not run independently, not to mention the more critical pons cerebellum does not matter) In the cruel natural environment, injury equals death. We know that white blood cells attack diseased cells by type. One organ necrotic lesion cells are cleaned up by white blood cells, and another good one is attacked by no difference. Paul has one eye injured. It is for this reason that blindness is quickly lost. The double-headed or multi-headed creature is slashed by the hero of the squadron, and the whole head is ok. But in the natural environment, there is such a good thing. When a brain is created, it will definitely hang on the body and continue to rot and necrosis. Hundreds of the entire body died of infection, and backup has no meaning at all. And evolution is not omnipotent, some genes are not easy to mutate, why are all terrestrial vertebrate animals with two pairs of limbs? The ancestors of terrestrial animals are finfish with strong fins, while the number of fins in finfish is not necessarily four pairs. But there is no way, only the ancestors of our four pairs of fins successfully landed and escaped the end of the Devonian extinction, so now the land vertebrates are two pairs of forelimbs with two pairs of hind limbs, which can only be degraded and disappeared. By the same token, the insect class has a total of one or two million animals, all of which are six feet, because their ancestors are six feet. Although the insects of many insects and crustaceans are very similar in lifestyle, and the evolution of the insect class seems to be omnipotent, there are even indigo, the devil that can develop abnormally, but no insect can The scorpion spider grows 8 feet. Therefore, even if there are some useful and uncomplicated structures, they can't grow out if they don't grow out. Since the higher-level animals have started to eat in the direction of movement, the two heads are not worth choosing. Even if their offspring have individual needs, they are too difficult. I have been thinking that if a food-borne animal can evolve a structure similar to a spear on a front paw, even if there is no venom gland, the forelimb that is much longer than the carnivorous canine and flexible and powerful will definitely increase the planting. The animal's self-defense ability to prey animals can only seriously damage the hunters when the predators rush over, and at least can greatly reduce the income expectation of hunting, fundamentally changing the appearance of the food chain, making pure hunting species Significantly reduced, the vertebrate circle also began to become mostly omnivores in the arthropod circle. However, vertebrates have landed for hundreds of millions of years. No one has evolved this structure. Instead, it has a lot of short spears on its head. Unfortunately, it is generally not very strong and very clumsy. It has no eggs. As for the conjoined animals with abnormal embryonic division, not to mention the independent species, fear that even the mutant individuals are not counted, the degree of conjoined is not the same, the symbiosis details are very different, they are not discussed, and no individual has a competitive advantage.