Why can some animals regenerate limbs but humans cannot?
All organisms, including humans, have the ability to regenerate something in the body. But the process is much more developed in lower organisms such as plants, protists — unicellular organisms such as bacteria, algae, and fungi and many invertebrate animals such as earthworms and starfish. These organisms can grow new heads, tails, and other body parts when injured. Scientists don’t know why mammals don’t have the same ability to grow new limbs. But they think it is because mammals have more complex biological structures; limb regeneration would require sophisticated controls to ensure that limbs and organs don’t grow out of control. Humans, for example, are already equipped with safety mechanisms to ensure that individual cells don’t grow uncontrollably. But these mechanisms wear down as a person ages and cancer is often the result. Nevertheless, mammals do regenerate skin, muscle, and blood. Scientists are just beginning to learn about other types of cells, such as those in the bra
