Why can't humans and other animals regrow limbs but other parts of our body can heal such as skin?
I know that a starfish can regrow limbs and many other creatures can. Why can't mammals and birds regrow limbs?
- DixonLv 71 month ago
They are just too complex to grow from a severed surface. Skin and bone can regrow and knit breaks because it is essentially just extending a material by making more of the same. But if you were severed just below the shoulder, the regrowth would need some way to start an elbow, a wrist, fingers all that cartilage and so on and sort out how to join up the veins and nerves etc.
The other things is, that is not how we grow limbs in the first place, ie we don't grow them outward from a surface.
Creatures such as crabs that can regrow limbs (often rather poorly) have a much more simple limb structure, which is an aspect of just being absolutely smaller. And since mammals can't regrow limbs, the evolutionary pressure is to repair the surface injury, ie skin.
- 1 month ago
i'm just gonna' speculate about this … perhaps mammal's genome was not programmed to replace such appendages. bone tissue does grow, however.
for instance, if someone breaks a bone … the doctor then "sets" the bone with a splint or a sturdier brace … over a week or two … you can actually see microscopic filaments joining the two pieces of bone. x-rays can show evidence of this phenomena.