“A man and a spider had a common ancestor”: biologist Sergei Glagolev said that scientists today know about evolution

Many biologists' claims may seem absurd at first glance. For example, that whales are descendants of hippos. Or that all people living on Earth descended from one ancient woman, which means that we are all relatives. But these theories actually have a scientific basis.

About these and other discoveries told at the forum "Scientists against myths" researcher and teacher Sergei Glagolev. Forum organizers - ANTROPOGENESIS.RU - posted a recording of the lecture on their YouTube channel, and Lifehacker made a summary.

Is it true that there are no remains of extinct and transitional species on Earth?

Evolutionary biologists often argue with creationists. The latter argue that all plants and animals, like man, arose on the planet in the form in which they are now. And that there really was no evolution, and the conclusions of biologists are far-fetched. This means that transitional species - intermediate between ancient and modern animals - could not be.

One of the arguments of creationists sounds like this: if hundreds, if not thousands, of extinct species lived on Earth, then the entire surface of the planet would be strewn with their skeletons. However, we see nothing of the kind. So the evolutionists are wrong.

Indeed, our planet is not littered with the skeletons of rats or bats and mountains of dried insects. But we know for sure that these creatures often die. But almost all organic matter is quickly destroyed, especially if the animal did not have a strong skeleton. The same thing happened with transitional species - most of their remains simply have not survived to this day. Especially if these species were rare and did not exist for long.

However, scientists still find massive skeletons of extinct animals. For example, it turned out that the bones of marine life are well preserved in sedimentary rocks. So the researchers found enough skeletons of sea urchins to see how this species gradually changed.

Scientists have been lucky: they have discovered an almost complete range of gradually changing organisms. And they saw, for example, how a horny outgrowth gradually appeared at the front end of the body in animals, and then increased. The hedgehogs used it for breathing.

In fact, there are many such finds. Exploring the layers of sedimentary rocks, biologists have repeatedly concluded: yes, transitional species did exist in the process of evolution.

Is it true that there can be no transitional steps between modern species

Creationists do not give up and say: but we do not see how right now one species is changing into another. We do not fix any intermediate forms. So they don't exist, and evolution is still a myth.

But here the question arises, what is a species. To find the exact definition, you can observe who the representatives of a particular species consider as their own, and who as strangers.

For example, in nature there are several species of white-headed gulls. They are very similar, and scientists cannot always tell them apart. But the seagulls themselves cope with the classification perfectly. They unmistakably define their own not by appearance, but by characteristic postures. And also by the cries that males make during courtship. As a result, seagulls pair up only with members of their own species, and ignore strangers. And maintain a clear boundary between species.

But animals and birds of other species may behave quite differently. For example, we all know that there are polar and brown bears. These species, according to scientists, appeared more than half a million years ago. No one will confuse a polar bear with a brown one - they definitely differ in appearance and live in different ecosystems.

But it turns out that there is no reproductive isolation between these species. Polar and brown bears interbreed. They give birth to healthy and full of life descendants, who can also actively reproduce. And to determine that white and brown are not one species, but two different ones, we can only use DNA tests.

Now let's turn our attention to people. We know that there are three main races, and there is no reproductive isolation between them. DNA analyzes show us that we have not three species, but one. If evolution had developed differently, and the representatives of three different races would have been isolated from each other, it is possible that the races would have taken shape in three separate species. But now this is not the case, and we conclude that the difference between races is our intraspecific differences.

It is all the more difficult to predict whether the changes that have appeared will be fixed and whether they will lead to the formation of a new species. If they bring it, it means that the current state will turn out to be an interspecies transition. No, it will turn out that all changes will remain within the framework of intraspecific differences.

But scientists no longer doubt that new species can appear not in hundreds of thousands of years, but in just a couple of centuries. For example, like motley flies that live on apples. Biologists know for sure that they appeared only in the 19th century. So the evolution continues.

Are there really no transitions between different types, classes and units?

Creationists continue to insist that evolution is overstated. They say: well, let's not talk about close, very similar species. But between different types and classes there definitely cannot be transitional forms. It's absurd to think that birds evolved from fish! Let's deal with this statement.

Paleontologists clarify: amphibians, or amphibians, originated from fish. Scientists really found about ten transitional forms from one class to another. That is, biologists have no doubts that ancient fish were the ancestors of amphibians.

Between the ancient animal-like lizards and mammals, they also found an almost complete series of transitional forms. If we talk about birds, then scientists have definitely found out that their ancestors were also dinosaurs. Yes, those ancient creatures that did not look like modern birds at all. All transitional forms that were necessary for such a conclusion were discovered by paleontologists.

In addition to paleontology, another science helps to deal with transitional forms. Conclusions about the ancestors of various animals can be verified by molecular biology. Scientists determine which ancient and current inhabitants of the Earth have common elements in DNA, and draw conclusions about their family ties.

For example, it was molecular biologists who proved that whales are close relatives of hippos. Yes, evolution does not necessarily follow the principle “from simple to complex forms” and “from sea to land”. It can also move in the opposite direction. And whales are closer to hippos than, for example, pigs.

Paleontologists have searched for ancient artiodactyls - the ancestors of the current hippos. And indeed they found both the artiodactyls themselves and the transitional forms from them to whales.

But that's not all. Comparative anatomy tells us that all modern species with bilateral symmetry must have had one common ancestor. This is a fairly simple organism, which first extended its mouth. Then it closed in the center of the body. At one end, the mouth opening was delighted, and at the other, the anal opening, and a through intestine turned out. On the sides of the intestine, symmetrically to the axial line, additional segments were formed. And then there was the brain and the rudiments of limbs.

So man and spider did have a common ancestor.

Why do scientists sometimes refute their own hypotheses

Yes, it happens. Sometimes there are discoveries that refute yesterday's hypotheses. And then scientists change their conclusions.

For example, today we are sure that all modern humanity came from one woman. Or from several, but those who were very close relatives to each other. That is, they still had one ancestor.

Of course, the descendants of many other women lived on earth. But over time, each such kind was interrupted. One is earlier, the other is a little later. But one day the family was left without new descendants and died out.

Approximately 150-200 thousand years ago, humanity went through a "bottleneck period" - one of several in its history. At this time, our population has dropped dramatically. According to some reports - up to five thousand individuals, and our species was very close to extinction.

As a result, almost all genetic lines were interrupted. The descendants of only one woman survived and survived to our time. It is she who is “mitochondrial Eve” or “lucky mother”, as scientists call her, and is our common foremother. Biologists have recently determined that she lived about 140-150 thousand years ago, although it was previously believed that she was older.

Let's see what new data will bring us future research. And we will continue to study the evolution of all life on Earth.