I remember that I once attended a seminar in which the speaker talked about the heart rate of different kinds of butterflies. Normally, the heart rate of the adult butterfly will be more complex than the heart rate when it is in the larvae form. However, there are some species that have complex heart rates even when they are in the larvae form, and there are others that have simple heart rates even when they are in butterfly form.

So if we are talking about the butterflies' heart, we can say that some species' heart are younger than their real age, while others are older than their real age. What is the name of this phenomenon?

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    $\begingroup$ I'm very confused about what you are asking. Your title is about "being younger than usual" and your question seems to be about either the rate of heartbeat or the complexity of heartbeat. I would suggest posing a clearer question. $\endgroup$ – akaDrHouse Oct 24 '15 at 16:55
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    $\begingroup$ I'm not sure about a general biological context, but an old word for looking younger than one's years is neanimorphic. A search on pubmed found zero results for this, so it is probably not the term you are looking for. $\endgroup$ – akaDrHouse Oct 24 '15 at 17:18
  • $\begingroup$ Well looking younger or having features of a youngling is called neoteny but I don't think you are referring to that. $\endgroup$ – WYSIWYG Oct 26 '15 at 6:27
  • $\begingroup$ @WYSIWYG yes, that's the word I'm looking for. May I ask why you don't think I'm referring to it? $\endgroup$ – Ooker Mar 18 '20 at 8:18


Neoteny (/niˈɒtəni/), also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal. Neoteny is found in modern humans. In progenesis (also called paedogenesis), sexual development is accelerated.

Both neoteny and progenesis result in paedomorphism (or paedomorphosis), a type of heterochrony. Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.

Both neoteny and progenesis cause the retention in adults of traits previously seen only in the young. Such retention is important in evolutionary biology, domestication and evolutionary developmental biology.


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