How does regeneration occur in animals?
Regeneration is the biological rebuilding of damaged or lost cells, tissues or body parts.
Biological mechanism and evolutionary explanation
After wound closure, stem cells or reprogrammed descendants of mature cells may proliferate and differentiate. Axolotls can replace limbs, sea stars arms and planarians large body regions, but capacity and mechanism differ. Nerves, vessels, muscle and skeleton must reconnect in the right positions. Biological traits do not arise because organisms consciously need them. Heritable variation and natural selection can change the frequency of traits affecting reproduction over generations. Similar outcomes may evolve through different mechanisms, and costs and benefits depend on context.
Examples, limits and research methods
Regeneration is not unlimited; age, injury location, infection, energy and species matter. A detached sea-star arm does not produce a new individual in every species or circumstance. Research offers clues for medicine, but another species' ability cannot simply be transferred to humans. Researchers combine comparative anatomy, behavioral observation, experiments, genetics and monitoring. One striking example is not treated as a universal rule, and alternative explanations are tested. Animal welfare, permits and minimal disturbance are part of study design.