Before, people believed that life forms were fixed, such as sheep, their past and future could only be sheep.
However, Darwin broke this tradition, and he believed that creatures can create countless most beautiful forms of life through evolution. The idea of
is very groundbreaking, because it is difficult to imagine how evolution changes life forms based on the time scale of human life span, but as more and more data accumulates, Darwin's idea does not seem to be very correct.
For example, the crabs we serve on the table, biologists have observed that this life form has appeared on Earth at least 5 times. These species in classification have eventually moved to the same form.
actually has many such examples in nature. Evolution happens all the time. It may indeed be as Darwin imagined that countless species can be created and appeared, but the forms of these species exist seem to have a limit, and not many.
© Hans Hillewaert
Five types of crabs
Crabs belong to a crustacean, and a more accurate classification is veritable. From the literal perspective, they are an animal group with 10 legs.
Decapitate is the most abundant species among crustacean , which may have more than 9,000, but they generally have only two forms:
One is like a lobster, with a thick and developed muscle abdomen (when it is served on the table, this part is the main part). This structure allows them to eject back quickly with a light shot, thus escaping from predators;
The other is like a crab, with a compressed flat abdomen, and then a shell is covered on it, which allows them to hide in the narrow cracks of stones for protection.
Because this structure of crabs does not require a strong and concentrated muscle structure, crabs are not as easy as shrimps.
There are now five types of "crabs", the most common type is the real crab that is almost invisible on the abdomen. There are about 4,700 species in the world.
The crabs we are familiar with basically belong to this category, such as river crabs, hairy crabs, shuttle crabs, , etc. These crabs have existed in this form for a long time, and their ancestors and their ancestors have basically looked like this.
However, some real crabs are now developing "backward" and gradually straightening their abdomen.
Another type of "crab" is a fake crab that belongs to the different tail under the order, which is also called the tilted tail under the order. The characteristic of these fake crabs is that their tails are asymmetric, and their ancestors look more like prawns.
Milk crab
There are four different "crabs" in the order of the order under the different tail, namely Miank crab (long-haired crab), porcelain crab (small crab with only four pairs of feet), stone crab ( king crab , etc.), and Australian hermit crab.
These five "crabs" have roughly the same shape. Their compact bodies are more defensive and can move to both sides faster, but they all evolve independently.
Porcelain crab
In other words, "crabs" are not a real group of biological groups, They are a collection of branches on the decapoda tree, but they evolve to make each other look the same .
The same end: evolution has been shaping similar lives
In nature, "crabs" are not the only ones like this, most creatures are like this - they come from different groups of organisms, but eventually they all go to similar forms.
is more distant with birds and their distant relatives.
If we were put in the Jurassic, although the animals and plants of that era were very different in classification from now, at least one thing we may not be too unfamiliar with is that we can see "birds" parked on the branches.
Although paleontology now has different opinions on the evolution of birds (new birds), one thing is basically certain, that is, all birds today evolved from those feathered ground dinosaurs.
Little Thunder Dragon ©Fred Wierum
However, in the era of dinosaurs, some dinosaurs have used their feathers to decorate their wings and fly into the sky, enjoying the ecological niche that birds should have now, such as the small theropod dinosaur discovered in Liaoning - Little Thunder Dragon.
Unfortunately, models restored through fossils may be very different from the original appearance of animals, and it is difficult for us to judge whether the same thing is really happening constantly.
The good news is that there is another good example to prove this, that is, our biological population - mammals.
There are now two major types of mammals living on the earth, namely placental animals (including us) and marsupial ( kangaroo , etc.), both of which evolved from common ancestors about 100 million years ago.
However, now marsupials live mainly in Oceania and the Americas, while placental animals live in more places, this isolation leads to two almost independent "evolutionary experiments".
As of now, the result is that both marsupials and placenta have evolved " mole ", "mouse", " anteater ", "flying rat", "cat", and "wolf".
Although these animals come from completely different branches, the physical details they get are surprisingly similar. The reason for this situation in
is actually very simple. In one term, it is to explain it in convergent evolution - organisms have evolved similar body structures in order to adapt to similar environments.
However, it is a bit surprising that convergence evolution actually occurs in smaller units, from the similarity of a single organ to the similarity of a molecular level.
For example, our eyes may be the most interesting organ in the human body. It completes a photo-taking function through lens, iris , retina and other structures, but the octopus far away in the deep ocean also gets an eye similar to us and has a photo-taking function.
If more generally speaking, the eyes may have evolved independently for 40 times in different animal groups, even box jellyfish without brains, with lens-shaped eyes at the bottom of its four tentacles.
Of course, except for the eyes, structures such as jaws, teeth, ears, fins, legs, wings, etc. are constantly evolving independently in the entire animal tree of life.
Recently, scientists have also found that this situation also occurs at the molecular level. Opsin molecules in our eyes convert photon into chemical energy, allowing humans to see that this is very similar to opsin molecules in box jellyfish, while the two evolve completely parallel without any "reference and reference".
Last
We often say that the emergence of humans on Earth is purely accidental, but it is not difficult to find from this convergent evolution that humans may not be unique at all.
at least "get" some of the most critical factors of human beings - such as curiosity, language, use of tools, learning... etc., are common in the animal world.
In fact, if this question is thought in a larger direction, then we even have reason to believe that aliens (if life evolved elsewhere in the universe) will not be too strange to us.
