In the middle of the 19th century, scientists hypothesized that in intrauterine development, a child goes through all stages of the evolution of a species. From a fertilized egg, it gradually turns into an intestinal hydra, then into a fish with gills, then an animal with a tail, and finally becomes a man.
It has long been proven that this hypothesis is, to put it mildly, inaccurate, but the phrase "ontogenesis (the individual development of an organism - primarily intrauterine) repeats phylogeny (the historical development of a group of organisms)" is so firmly entrenched in the minds of the masses that some are still believe.
It all began in 1866, when the German materialist biologist Ernst Haeckel, who studied radiolarians, jellyfish and lime sponges, decided to find proof of Darwin's theory. Having studied the uneven-aged embryos of humans and animals, he found similarities between them. The tail and gills of a human embryo are no accident, Haeckel thought. It's not for nothing that Darwin believes that we are descended from animals. But what if each living creature in its own development briefly and quickly repeats the development of its species?
The churchmen did not like Haeckel's idea, but they liked his fellow scientists - it was renamed the biogenetic law. But, unfortunately, it was not possible to prove the law in its original formulation. What was considered indisputable at first glance turned out to be mistaken on closer examination.
At present, embryologists have revised the Haeckel-Müller-Baer law, but the myths associated with it are still alive. We will debunk them.
Are there gills?
It would seem that the gills of the embryo are indisputable proof of our place on the tree of evolution. But modern embryologists and anatomists have discovered a curiosity: Haeckel made a mistake - he described only the appearance of embryos, without going into details of their structure. What Haeckel took for gills turned out to be just folds of tissue in the human embryo - the predecessors of the head and neck.
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Since then, these folds are called (by tradition) gill arches. Although it is more correct to call them visceral from the English word "visceral" - "internal", because internal organs are formed from them. Gill slits, as in cold-blooded animals, do not form in human embryos.
What about the tail?
In all the pictures, the embryos are shown as tailed. It turned out that human embryos have more vertebrae than adults. If we have 33-34 of them (sometimes 4 or 5 coccygeal ones), then 38 of them are laid in the mother's womb. The rest are reduced.
But the long "tail" of the embryo is not only those "extra" vertebrae. It's just that the axial skeleton, like the nervous system, grows more slowly than other organs and tissues, and therefore several large sizes are laid at once in comparison with the entire tiny organism. So it turns out that the spine is long and the head is big.
Fluffy babies
Sometimes in newborns you can see fluff on the body - lanugo. Then it disappears (usually lanugo appears at 28 weeks of pregnancy, and disappears by 40). Maybe this is the legacy of monkeys - our shaggy ancestors? But nothing happens in the body just like that. An underdeveloped fluff performs a protective function. As the proverb says, "I would have known where I have to fall - I would have put straw." Babies are "laid with straw" by nature itself: what if you have to be born earlier by 2-3 weeks, and the thermoregulation system is not yet ready for cold air. So the little fluff will come in handy.
Are our smaller brothers really our brothers?
Now the opinion of embryologists is unambiguous: from the very beginning, the human embryo is a person, and not someone else. Of course, we are not difficult to compare with other animals: we consist of cells, breathe oxygen, have a head and 4 limbs, and Darwin's theory is still recognized as official.
By studying embryos, scientists compare different species to determine their evolutionary relationship. But now they do this not by external signs, like Haeckel, but by genes that manifest themselves in the same places of the embryo. For example, genes that synthesize proteins of the nervous tissue are activated at the head end - the brain will be here. In the same way, you can compare the genes and proteins of the liver, kidneys and all other organs and tissues in order to understand from which groups of germ cells that is formed.
Funny world history
Educators-psychologists did not resist the temptation to use Haeckel's biogenetic law. So at the end of the 19th century, G. Hall's theory of recapitulation appeared - the concept of mental development, which considers the formation of individual consciousness as an abbreviated reproduction (repetition) of the historical stages in the development of consciousness of the human race. That is, after birth, the baby, having already passed the "stages of the animal world" by that time, must begin to go through the stages of civilization development. And what are we seeing?
First, he learns to walk and makes inarticulate sounds - like some prehistoric man. Then he plays in the sandbox, launches paper boats - neither give nor take, reproduces ancient Egypt and Phenicia. Over time he masters the simplest mechanics, writing - as if in antiquity or the Middle Ages.
Achievements are becoming more difficult every year. And it must take many years before, through the efforts of many teachers, the child … goes to college.
We cannot say who is right: those who say that our ancestors are monkeys, or who claim that man was created by a higher power in the form in which he is now. We do not set ourselves such global goals. But now we can say with confidence: the human embryo at all stages of development, from conception to birth, is not a tadpole or a fish, but a future person.
Tatiana Ryabinkina