The migration of vertebrates from water to the land-air environment was a turning point in the history of the biosphere. But this evolutionary leap had serious side effects: In reptiles, birds, and mammals, it led to the loss of the ability to regenerate lost body parts. In a new paper, biologists examined the genetic and evolutionary aspects of land development and found that the sharp decline in regeneration became a kind of “punishment” for animals to adapt to a different environment.

For most of its history, life on Earth was essentially just “aquatic life.” The situation began to change only at the beginning of the Paleozoic era, with the appearance on land of the first primitive plants – descendants of green algae, fungi and invertebrates such as scorpions.

Chordates, or rather animals with a backbone, came to land much later, when there was a certain company there. The first traces of vertebrates on land were left by “fish-pods” such as tiktaalik, which were a transitional link between fish and amphibians.

Later vertebrates became the largest animals of the land-aerial environment and an important component of their ecosystems. From amphibian precursors (or amphibians) came reptiles, followed by mammals and birds. However, the dominance of vertebrates on land has been a loss for them: they regenerate much worse than Anamnias (lower vertebrates) and many invertebrates.

Indeed, fish and amphibians can easily and fairly quickly regrow if they lose a large part of their body, for example if someone bites them. For example, the axolotl can regenerate limbs, the heart, and even the brain after amputation.

Reptiles, and especially birds and mammals, are a completely different matter. There are only a few exceptions, including intentional shedding, such as lizards that can regenerate their tail after loss. Other terrestrial vertebrates (amniotes) cannot even regain a lost finger. Their self-healing ability is limited due to wound healing and “regrowth” of certain organs, such as the liver.

Scientists from the Institute of Biomedical Sciences of the Russian Academy of Sciences and the Russian National Institute of Medical Sciences are authors of a new publication in the journal. Biology Reviews – He decided to find out how the loss of regenerative abilities is associated with a change in the living environment. Researchers hypothesized that dry land sharply decreased due to the emergence in vertebrates of new features that were more important for its development: immune complications, keratinization of the skin surface, transition to warm-bloodedness (homothermia), as well as an increase in body size.

Evolutionary rearrangement affected the genomes of animals: they lost many genes and regulatory regions of DNA (enhancers) that helped their ancestors. Currently, such restrictions are recorded in the genomes of higher vertebrates, including humans.

Scientists stated that animals learned to renew their bodies long before they lost the necessary genes. There are about 150 of them in total – fish and amphibians need them for the early stage of regeneration that begins immediately after injury. Unlike genes introduced later, early regeneration genes did not affect the embryonic development of the organism, so their elimination did not lead to lethal consequences for the animals.

The new paper also suggests that the most promising way to regenerate a limb in humans is to first create an embryonic embryo. It can be obtained from induced stem cells using tissue engineering. In the future, such a “form” should turn into a full-fledged arm or leg.