<p>No, an animal population that subsist solely by consuming its own members is not sustainable.  This is easy to see because there's no external energy input into the population (all energy comes from other members of the same population), yet the individuals will necessarily expend some energy in their metabolism (turning it into heat).  Eventually, if the population cannot find any other food sources, the individuals will die (and be consumed) one by one, until the last one will run out of food and starve.</p>

<p>That said, there <em>are</em> animal populations in nature where <em>some</em> of the individuals may subsist almost entirely on cannibalism.  This is typical of e.g. <a href="http://www.researchgate.net/publication/226857633_Cannibalism_in_teleost_fish" rel="nofollow">fish</a>, which are very tiny when born, grow gradually over their lifetime, and tend to consume prey smaller than themselves.  Thus, in small lakes that happen to host only one species of fish, it's not uncommon for the large adult fish to mostly eat smaller juvenile fish of the same species (which in turn eat plankton and invertebrates, providing an external source of energy to the system).</p>

CC BY-SA 3.0
2015-08-29T20:09:38.280Z
Ps. For an illustrative (and somewhat addictive) demonstration of size-structured cannibalism in a (virtual) population, go play a few games of [agar](http://agar.io/). :-)
Ilmari Karonen
CC BY-SA 3.0
2015-08-29T23:15:02.823Z
That game has already given me an (virtual) eating disorder.
IHaveNoMovieAndIMustScream
CC BY-SA 3.0
2015-08-29T20:04:16.053Z
2015-08-29T20:04:16.053Z
Ilmari Karonen
<p>Bit of a weird one, but here goes. Say there is a human society whose diet is 100% the human flesh of their own members. Would this society be able to maintain replacement population, or even <em>shudder</em> grow? I suppose figuring this out would require daily caloric requirements, caloric value of human flesh, length of gestation, average age and a host of other variables, but is there some economic principle to short-cut to a solution here? Apologies if you've been sick. </p>

CC BY-SA 3.0
2015-08-29T20:05:00.740Z
Anyway, shouldn't this be on [biology.SE]?
Ilmari Karonen
CC BY-SA 3.0
2015-08-29T20:15:52.143Z
I don't believe this question is on-topic here. I don't see how it is related to economics.
cc7768
CC BY-SA 3.0
2015-08-30T07:43:54.023Z
@cc7768 But but but it has math in it, and differential equations... I'm pretty sure we're the only ones using that!
FooBar
<population-economics>
Would a society of cannibals be self-sustaining?
IHaveNoMovieAndIMustScream
# Would a society of cannibals be self-sustaining?

(Asked by: username_0 on 2015-08-29)

Bit of a weird one, but here goes. Say there is a human society whose diet is 100% the human flesh of their own members. Would this society be able to maintain replacement population, or even *shudder* grow? I suppose figuring this out would require daily caloric requirements, caloric value of human flesh, length of gestation, average age and a host of other variables, but is there some economic principle to short-cut to a solution here? Apologies if you've been sick.

**Tags:** population-economics

> **Comments:**
> **username_1**: Anyway, shouldn't this be on [biology.SE]?  
> **username_2**: I don't believe this question is on-topic here. I don't see how it is related to economics.  
> **username_3**: @username_2 But but but it has math in it, and differential equations... I'm pretty sure we're the only ones using that!  

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## 1 answers

### Answer by username_1 on 2015-08-29. Score: 4 | Accepted answer

No, an animal population that subsist solely by consuming its own members is not sustainable. This is easy to see because there's no external energy input into the population (all energy comes from other members of the same population), yet the individuals will necessarily expend some energy in their metabolism (turning it into heat). Eventually, if the population cannot find any other food sources, the individuals will die (and be consumed) one by one, until the last one will run out of food and starve.

That said, there *are* animal populations in nature where *some* of the individuals may subsist almost entirely on cannibalism. This is typical of e.g. [fish](http://www.researchgate.net/publication/226857633_Cannibalism_in_teleost_fish), which are very tiny when born, grow gradually over their lifetime, and tend to consume prey smaller than themselves. Thus, in small lakes that happen to host only one species of fish, it's not uncommon for the large adult fish to mostly eat smaller juvenile fish of the same species (which in turn eat plankton and invertebrates, providing an external source of energy to the system).

> **Comments:**
> **username_1**: Ps. For an illustrative (and somewhat addictive) demonstration of size-structured cannibalism in a (virtual) population, go play a few games of [agar](http://agar.io/). :-)  
> **username_0**: That game has already given me an (virtual) eating disorder.  

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