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Take any well-known aggressive/dominant/predatory animal - wolves, big cats, bears, dragons, etc. Now say this animal were to have two heads, each equal in all capacities. What would realistically change from it's single-headed brethren?

I can imagine two possibilities:

1) Two heads would share (and split) the impulses of one body, reducing/sharing the aggression and impulses between them. For example, if a single-headed lion needs to eat a whole gazelle to feel satisfied, each head of a two-headed lion may think it only needs to eat half a gazelle. Two lion heads, each perceiving a fraction of the body's hunger, may be less driven to hunt.

2) Each head would get the full-blown drive of the body - in essence, a two-headed lion wants to hunt and eat two gazelles. This would surely make the multi-headed variety grow larger and become more dangerous, as it consumes and hunts twice as much with (arguably) twice as much drive.

Do either of these options seem more realistic over the other? Are there additional factors I'm not considering?

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    $\begingroup$ Amongst many real-world examples of animal development resulting in viable conjoined animals, two-headed snakes are rare, but can even survive in the wild. en.wikipedia.org/wiki/Polycephaly#Reptiles $\endgroup$ – Neil Slater Oct 21 '14 at 16:31
  • $\begingroup$ I assume the heads are side-by-side, and not located on another part of the animal? I think the positioning of the heads is the biggest issue. $\endgroup$ – Rowanas Oct 21 '14 at 21:56
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In many ways the animal would function the same as it does with a single head, it would eat until full. It would hunt when hungry, sometimes the heads would fight each other but mostly they would get along. The "I'm full" hormones the stomach sends would reach both heads just fine for example.

The main problem though is that the animal is just less well adapted as a predator than a single-headed version of itself. It's less well balanced, it's not as aerodynamic, it finds it harder to pass through small spaces or dodge obstacles. Reflexes are slowed by the two heads having to co-ordinate their actions.

In fact about the only advantage it does have is that one head can keep watch while the other eats or sleeps. For apex predators though that is rarely a requirement and unless for some obscure way it evolved that way animals don't have the intelligence to co-ordinate that sort of activity. Not to mention the fact that the body would still want to all sleep at once even though the heads disagreed.

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  • $\begingroup$ All good points - no way around it, it seems they'd just be inferior unless they had the time to evolve and adapt. Thanks! $\endgroup$ – CodeMoose Oct 23 '14 at 12:51
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I think your first option would be closer to the truth. Both heads would receive the same 'hunger' impulses from the stomach. So it would go hunt, but with two heads eating it's prey, it would fill up it's stomach twice as fast. Both heads would also get the same 'I'm full' impulse from the stomach about the same time. The biggest difference would be in how fast it could consume the same amount of prey.

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