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I recently discovered (via a friend) that relative to size, kiwi's produce the world largest egg. I also found out that when the egg does hatch, the chick is practically an adult in its own sense. This made me wonder, could there be a species that never grows in size? To my knowledge this is rather unlikely, but theoretically it could be possible.

Could a species come into being that does not grow (barring puberty)? How could such a species evolve and what would its evolution be?

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closed as too broad by Aify, John Dallman, Hohmannfan, Green, JDługosz Nov 15 '16 at 23:03

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.

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    $\begingroup$ What do you mean by "does not grow"? The newly born or hatched younglings must by necessity be somewhat smaller than their mother because they are produced by her and some mass must remain with the mother afterwards. If you mean that individuals do not grow after achieving adult-like form then this is not uncommon with holometabolic insects, which have abrupt transitions between larva, pupa and imago forms -- see en.wikipedia.org/wiki/Holometabolism. $\endgroup$ – AlexP Nov 15 '16 at 19:02
  • $\begingroup$ It may be helpful to define what "growing" is allowed and what is not. For example, not repairing damaged tissues would result in extinction. However, not getting larger would probably work - maybe phrase it as "Be born at full size and have the mother just grow during pregnancy" $\endgroup$ – Zxyrra Nov 16 '16 at 0:10
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Physics says no. Our young are smaller than we are because we cannot birth young equal to our own size.

Even your example, the kiwi bird, has an egg 15% of the body weight of the female adult mother.

However, you did say "barring puberty" which means that, really, you could birth a child that's tiny, and it just grows a whole bunch during that time, while for some reason not growing at all prior to that.

This doesn't track in any known biology, even in the example you gave.

I mean, there's some terrible things I can think of, like the baby kills the mom on the way out, because it's so large and takes so many resources to grow, and that the mother would not be able to move at all during most of the pregnancy.

Notice that your example (15% of body weight) is supposed to be a big deal, biologically, so imagine if you upped that considerably.

Maybe you mean something different than how the question is asked? If so perhaps edit it. But, as it stands, this is actually not possible. Insects come the closest to this.

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The geometry of this species is challenging. A female of this species would need to be able to produce an egg inside themselves and that egg would need to be big enough to contain not only a full grown offspring, but also all of the nutrition needed during its gestation.

She'd need to be made out of spandex to even attempt it.

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