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listen to part of a lecture in a biology class.

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So let\'s go back to our discussion of how animals defend against predators.

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Here\'s an interesting phenomenon that caught the attention of some researchers.

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Female mule deer aggressively defend their young against predators.

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Not exactly shocking news, but there\'s more.

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They defend the young of other deer too, even ones of a different species.

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And not only that,

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they will even leave their own young alone to do so.

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This is certainly not common behavior among deer

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in other species,

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like the white tailed deer,

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if a mother senses a threat, she will only defend her own young.

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So why is the mule deer\'s behavior so different?

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To find out, the research team conducted an experiment at a cattle ranch where both these species of deer often gather,

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and to study this unusual mule deer behavior,

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they decided to simulate a threat from a predator,

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a coyote.So they recorded distress cries of different baby deer, different fawns.

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Then they placed loudspeakers in places where the adult deer could hear those recorded cries and respond to them,

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and they looked at how well different hypotheses could explain the mule deer\'s behavior.

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The first hypothesis was

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maybe the mule deer were defending the fawns of other deer simply because of confusion,

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what we call a recognition error.

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Maybe they couldn\'t tell the difference between the distress cries of their own fawns and those of others.

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And in fact, mule deer did not seem to distinguish between the cries of their own fawns and cries of other mule deer,

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or even white tailed deer, including adults

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and a mother. Mule Deer always responded the same way,

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even with her own fawns standing right in front of her.

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But in such cases, how could there be any confusion?

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Obviously the cry was not from her own fawn

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even so she approached the loudspeaker just as aggressively,

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not what you\'d see a whitetail doing,

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but in fact,

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all female mule deer responded aggressively,

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even ones that were not mothers of young fawns.

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So recognition errors may well occur,

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but I think we\'d better look elsewhere for our answer.

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Okay, the second hypothesis, let\'s call this the

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bedded fawn hypothesis,

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that because the younger fawns stay in a nest or a burrow, and so they\'re called bedded fawns, as opposed to active fawns,

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the researchers reasoned that a mule deer with a bedded fawn might respond more aggressively to any distressed cry

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because her own fawn couldn\'t run away easily.

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She\'d want to keep the area around her offspring secure by standing and fighting.

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But mothers with bedded fawns did not respond more aggressively.

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So the third hypothesis,

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what\'s called reciprocal altruism.

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Now, altruism has a very specific meaning in the world of animal behavior.

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Simply put, it means that the behavior of one animal benefits others

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at potential cost to itself,

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which clearly describes what\'s happening here

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and reciprocal altruism,

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that\'s when animals do favors for each other.

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One animal will do something to help another,

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like share food,

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expecting that it will someday be on the receiving end

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a mother mule deer then might endanger herself to help others,

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so that those others might later on protect her,

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or, in this case, her fawn.

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But theoretically, it only makes sense for her to help individuals that can be relied on to reciprocate,

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to help her out in a similar situation.

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So the rule about reciprocal altruism is

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that an animal has to be able to recognize who is helping

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Remember, though, that a mule deer cannot seem to identify the cry of its own species,

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much less of its own offspring.

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So why do mule deer choose to protect the young of others?

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Or is this the wrong question to ask?

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Maybe they\'re just sort of programmed to react mindlessly to any predatory threat

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without stopping to consider whether it\'s their own offspring or others that they\'re protecting.

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In any case, we\'ll need more evidence to figure out just how altruism is involved here,

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and that will require a good deal more research.

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