The rule is to reduce energy flow. It appears that there are limitations of energy distribution in all forms of life. Most life forms have a unique trait that requires a higher amount of energy to utilize it. For example, the human brain is expensive to run, the same is true for a cheetah that can run at high speeds to catch its prey, the eagle that has excellent vision and can see its prey from a long distance in detail, and on and on. No one species "has it all" in high energy features.
By re use in designs or altering it is much cheaper than building from scratch. We follow this same logic in manufacturing. If there are new features that are viewed as started from scratch I would think that there was no other alternative.
The fact that creatures appear to built just good enough not perfect indicates to me an energy limitation is in place. In insects it is the complete opposite in that some of them appear to be overly engineered perhaps because of their small size.
Edited by barbara, : No reason given.