When a baby is being developed inside the womb,

1) how does the baby's body know a finger, or any other part of the body, has been fully developed?

2) following question, how does it "stop" the development of that part? What kind of signals are being communicated here?

3) I have hairy arms. The length of the hair is almost the same length if i don't cut it. If it breaks, it grows back almost the same length. How does the body know the current length and how to stop when it reaches the "target length"? Is it the same "procedure" as the development of parts inside the womb?


closed as too broad by Remi.b, The Last Word, Bryan Krause, David, De Novo Oct 22 '18 at 18:59

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    $\begingroup$ Welcome to Biology.SE. The two first questions are related, the third question is quite different. Please always narrow down your post to a single question. Also, the first two questions are in themselves already quite broad. You might want to read a bit more about developmental biology $\endgroup$ – Remi.b Oct 11 '18 at 17:18
  • $\begingroup$ For the third question, you might want to read related posts; Why does hair grow after trimming but remains at a constant length after a while? and Why can hair grow without limit while eyebrow cannot? $\endgroup$ – Remi.b Oct 11 '18 at 17:21
  • $\begingroup$ I am interested in the "communication part". I chose hair as an example because it regrows. I could have chosen anything that regenerates to the original shape in the body. $\endgroup$ – Carlo Santana Oct 11 '18 at 17:25
  • $\begingroup$ Is there a common "algorithm" the body follow for development and regeneration or is there different once for every scenario? $\endgroup$ – Carlo Santana Oct 11 '18 at 17:26
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    $\begingroup$ Yes, there is some kind of "algorithm". Describing this "algorithm" would require writing a whole book. And in fact many people have been writing books on the development of organisms. This is why the question is too broad in my opinion. Your question sounds to me like the question "Can you explain to me how biology works?" might sound to you. $\endgroup$ – Remi.b Oct 11 '18 at 17:28

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