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So we all know that Lemmings are known for following blindly to their death but that is not the reality.

I would like to create the myth in the real world, or rather I would like to know how such a creature could be created via evolution.

  • Creature must be a vertebrate
  • Creature must be at least as large as the average squirrel
  • Creature must follow a leader creature (specialized type)
  • Creature must follow without fear of death (if told to it will in fact run off a cliff)

How would a situation like this come about via evolution and real world science?

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    $\begingroup$ ants. (very large) ants. $\endgroup$ – Henry Taylor Feb 1 '16 at 21:15
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Social insects, like ants and bees seem to fit well to your behaviour description, however, they are too small.

The mammal species that has the most social insect like way of living is the Naked mole rat. They are:

  • Vertebrate, check
  • As large as an average squirrel, check
  • Follows a specialized leader, check
  • No fear of death, well, they look really brave:

naked mole rat

(Go through the list once more and think "humans".)

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  • $\begingroup$ Once again, reality wins the, "how would this weird thing happen in my imaginary world" $\endgroup$ – James Feb 3 '16 at 16:33
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Having intelligence actually makes this one easier. Brainwash individuals to do your bidding and send them out.

Human's have done this for centuries. One of the earlier known cases are the Assassin's (original). They trained to be killers and were sent out to kill targets dying if necessary for the "Old Man on the Mountain".

We still have people doing that. The kamikaze during WWII, where the Japanese pilots made a one way attack on Pearl Harbor for their emperor.

And today we have suicide bombers dying for the promise of 70 virgins and some power hungry nut job.

It's much easier to train an 'intelligent' animal to kill itself for the good of 'all'.

So human's meet all of your requirements.

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  • $\begingroup$ As far as I know the voluntariness of the kamikaze pilots is source of dispute up to this day, so I don't think they make a good example for your case. But the suicide bombers employed by ISIS/Daech or Al Quaeda or others would fit this quite well. $\endgroup$ – fgysin reinstate Monica Feb 2 '16 at 8:05
  • $\begingroup$ I knew someone would suggest humanity... $\endgroup$ – James Feb 3 '16 at 16:30
  • $\begingroup$ I couldn't pass it up. Lemmings, sheep, sheeple... $\endgroup$ – bowlturner Feb 3 '16 at 16:32
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Brain infection

There are a whole host (see what I did there) of mind altering infections in the world. Such as Toxoplasma gondii, which cause mice to actively seek out the smell of cat urine, or Rabies which causes uncontrollable aggression.

Most of these infections bring about these changes to cause the host to conduct behavior that is conducive spreading of the infection.

We could conceivably have an infection that manifests in filling some organ with a huge amount of pathogen, followed by a stage where the host runs uncontrollably. When the poor critter falls off cliff and impacts upon the ground it causes a small cloud of infectious splatter to whiff through the valley.

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  • $\begingroup$ Clever angle I like it $\endgroup$ – James Feb 3 '16 at 16:30
  • $\begingroup$ Or... scavengers will fight and snap over the corpse, each having some. $\endgroup$ – wizzwizz4 Feb 9 '16 at 16:46
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In evolutionary terms, a fear of death is a by-product of being required to reproduce at some time in the future, since those individuals without such a fear of death would be less likely to reproduce.

However, if we were to evolve a species where we have two classes of individual, one reproductive, the other not capable of reproduction, the non-reproductive individuals could evolve behaviours that would be counter-productive for a reproductive individual. This is a fairly typical hive system. The only necessary evolutionary step would be for the non-reproductive individuals to be permanently non-reproductive, since as long as the potential for reproduction in an individual exists, it must have an evolutionary need to survive.

Let us further suppose that this species environment contained many hazards of many different types, including geography, fauna and flora as threats. It may be too difficult to evolve to deal with all of these threats, but if a reproductive individual was accompanied by many non-reproductive individuals, then by observing the fate of these disposable individuals, the reproductive individual could by observation notice and avoid the hazard. Of course, the 'disposable' trap-springer would be disadvantaged, but its sacrifice would have increased the probability of its reproductive sibling successfully reproducing.

Such a creature by necessity would need to be fairly intelligent, enough so that the breeder would be able to recognise that one of the disposables has suffered a mishap. Since the ability to communicate often comes with intelligence, it can be expected that a breeder could direct its related disposables to test the ground ahead for hazards. These would be indicated by audible means, either an "I'm OK!", "There's trouble!", or a death cry that would indicate a particularly dangerous hazard. Note that even if there were hazards capable of eliminating a disposable silently, the lack of the "I'm OK!" calls would be an indicator of a hazard.

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  • $\begingroup$ Behaviors that get individuals killed would need to be sufficiently rare, but the requirements are rates that must balance, not a specific means of enforcing that. Fear (even assuming all fear is fear of death) isn't a logical requirement for that balance. Otherwise, I agree with your analysis. $\endgroup$ – The Nate Feb 4 '16 at 14:56
  • $\begingroup$ Why not make this age based instead of having two different classes of individual? It seems like it would make more evolutionary sense if the members of the species got suicidally brave after x years of being sexually active. That way, all members of the species are still contributing to the gene pool. $\endgroup$ – lucky.hooligan Feb 9 '16 at 17:16
  • $\begingroup$ @lucky.hooligan, because being reproductive leads to self-preservation, which tends to stick around even after becoming non-reproductive. Ask your post-menopausal grandmother if she would want to be something like a human land-mine detector, I'm pretty sure the answer would be "no". $\endgroup$ – Monty Wild Feb 9 '16 at 21:57
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Memetic evolution.

Having a complete species of animals evolve to destroy their own fitness by suicide is very difficult. In such cases, it would be easy for the animals to evolve mutations which stop this behavior, and it would greatly enhance their fitness.

However, it is nevertheless still possible to have a minority of the species act like lemmings, if a meme manages to spread within the population which encourages such behaviour.

An example would be clergy. They are (mostly) self-sterilised by means of a meme (religion), and such groups have existed for thousands of years. They mainly survive by drawing new memetic converts from the general population, while its existing converts die out. It is not implausible for such a system to form in nature, and other possible examples include terrorist suicide bombers who willingly go to their death for their religion or some other memetic cause.

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On a macro level, many animal species act like the made-up lemmings. Most of the time, predators and food supply keep the critters in check:

  1. With lots of food and few predators, the animal reproduces quickly.
  2. As the animal multiplies, they begin consuming the food more rapidly, and predators begin to increase
  3. Eventually, there are more critters than food, and more predators than critters; the critters starve and/or are eaten.
  4. With fewer critters, the predators die off and the food regrows, and the cycle begins again.

But what if there are no predators? Islands often have very small, specialized ecosystems; it's not difficult to imagine an island populated by nothing more vicious than a blue-coated critter with green hair and a long nose. In that case, the only limiting factor is food. But what if the food remains plentiful until a certain point, then almost overnight is gone? Rather than a slow, constant, more/less cycle, the food is almost a binary switch - food today, none tomorrow. This would have a huge impact on the survival of the critters. As their population grows, they come closer and closer to destroying their food source, wiping out the entire population. If their population grows too much, they may wipe out the species entirely.

So, nature installs a switch. The critters are natural introverts; the more time they spend near other similar creatures, the more stress-induced chemicals build up in their brains. As their population booms, more and more critters accumulate chemicals. At first, the chemicals have little effect, but eventually they cause the critters to essentially go insane, their desire to be away from other critters overriding their self-preservation. The critters will begin chasing other creatures in an attempt to drive them away; a stampede of critters begins, sweeping up a large amount of the population, and terminating in the ocean. The more stress chemical acquired, the stronger the desire to chase, and those initiating the chase are most likely to survive.

With a significant portion of the population gone, the rest calm down, and the cycle begins again:

  1. Critters reproduce
  2. Critters overpopulate and begin generating stress chemicals
  3. Super-stressed critters chase the rest into the sea
  4. Surviving critters begin repopulating

I realize this answer doesn't fit the criteria of followers and leaders, but it is how I imagine "suicide lemmings" would act.

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  • $\begingroup$ I don't see where this switch comes from. The critters who naturally evolve a tendency to run off the cliff will die out, while the critters who ignore them and stay alive will pass their genes on. $\endgroup$ – MichaelS Feb 9 '16 at 6:55
  • $\begingroup$ I've edited my answer to explain; critters that have the most stress are most likely to initiate the rush, but are also most likely to survive. $\endgroup$ – ArmanX Feb 9 '16 at 14:37

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