Human tail is like tech debt
You won’t see any appendage on newborns, because tails are removed by the end of embryonic development. “Why develop a tail in the first place”, you may wonder. My answer: Genetic mutations of adding apoptosis (“programmed cell death”) is safer than those of removing the tail-generating step.
In my answ er above, “safer” means “more likely to pass the filtering effect of natural selection”. Over the past 375 million years when we evolved from fishes (Elpistostege or Tiktaalik, to name a few possibilities), there are likely times that the tail-generating genes has been knocked out completely. Unfortunately, these intermediate species went extinct.
As paleobiologist Lauren Sallan stated, “it would be very difficult to get rid of [the tails] entirely without causing other problems.”
The same goes in software engineering. Old components can be hard to remove, because higher-level features may be built on them. Think about the great effort it took Facebook to replace their server-rendered PHP website with React.
