# Regeneration Abilities among Extant Animals Depend on Their Evolutionary History and Life Cycles

## TL;DR

This paper explains how animals' ability to regenerate body parts depends on their evolutionary history and adaptation to land life.

## Contribution

It proposes new hypotheses linking terrestrial adaptation to the loss of regenerative abilities through epigenetic and genetic changes.

## Key findings

- Animals that evolved from marine ancestors lost regenerative abilities during terrestrial adaptation.
- Terrestrial conditions like dryness and UV exposure hinder regeneration in arthropods and amniotes.
- Nematodes evolved eutely, which prevents regeneration and involves fixed cell numbers.

## Abstract

The present brief manuscript summarizes the main points supporting recently proposed hypotheses explaining the different distributions of regenerative capacity among invertebrates and vertebrates. The new hypotheses are based on the evolution of regeneration from marine animals to the terrestrial animals derived from them. These speculations suggest that animals that were initially capable of broad regeneration in the sea underwent epigenetic modifications during terrestrial adaptation that determined the loss of their regenerative abilities in sub-aerial conditions. These changes derived from the requirements of life on land that include variable dry and UV-exposed conditions. Terrestrial conditions do not allow for organ regeneration, especially in arthropods and amniotes. Nematodes, the other main metazoan group unable of regeneration, instead evolved eutely (a fixed number of body cells), a process which is incompatible with regeneration. All these changes involved gene loss, modification and new gene interactions within the genomes of terrestrial adapting animals that gave rise to sophisticated invertebrates and vertebrates adapted to living on land but with low cellular plasticity.