Regeneration is the ability of a fully differentiated organism to give rise to new individual organisms from its body parts. More complex organisms cannot give rise to new individuals through regeneration because:
(i) their body is highly complicated.
(ii) there are specific organs to do specific functions.
(iii) there is a labour division in the body of complex organisms.
(iv) regeneration is carried out by specialised cells which are not present in complex organisms.