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1 .listen to part of a lecture in a biology class.
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2 .So let\'s go back to our discussion of how animals defend against predators.
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3 .Here\'s an interesting phenomenon that caught the attention of some researchers.
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4 .Female mule deer aggressively defend their young against predators.
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5 .Not exactly shocking news, but there\'s more.
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6 .They defend the young of other deer too, even ones of a different species.
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7 .And not only that,
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8 .they will even leave their own young alone to do so.
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9 .This is certainly not common behavior among deer
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10 .in other species,
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11 .like the white tailed deer,
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12 .if a mother senses a threat, she will only defend her own young.
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13 .So why is the mule deer\'s behavior so different?
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14 .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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15 .and to study this unusual mule deer behavior,
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16 .they decided to simulate a threat from a predator,
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17 .a coyote.So they recorded distress cries of different baby deer, different fawns.
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18 .Then they placed loudspeakers in places where the adult deer could hear those recorded cries and respond to them,
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19 .and they looked at how well different hypotheses could explain the mule deer\'s behavior.
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20 .The first hypothesis was
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21 .maybe the mule deer were defending the fawns of other deer simply because of confusion,
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22 .what we call a recognition error.
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23 .Maybe they couldn\'t tell the difference between the distress cries of their own fawns and those of others.
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24 .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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25 .or even white tailed deer, including adults
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26 .and a mother. Mule Deer always responded the same way,
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27 .even with her own fawns standing right in front of her.
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28 .But in such cases, how could there be any confusion?
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29 .Obviously the cry was not from her own fawn
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30 .even so she approached the loudspeaker just as aggressively,
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31 .not what you\'d see a whitetail doing,
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32 .but in fact,
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33 .all female mule deer responded aggressively,
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34 .even ones that were not mothers of young fawns.
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35 .So recognition errors may well occur,
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36 .but I think we\'d better look elsewhere for our answer.
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37 .Okay, the second hypothesis, let\'s call this the
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38 .bedded fawn hypothesis,
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39 .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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40 .the researchers reasoned that a mule deer with a bedded fawn might respond more aggressively to any distressed cry
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41 .because her own fawn couldn\'t run away easily.
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42 .She\'d want to keep the area around her offspring secure by standing and fighting.
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43 .But mothers with bedded fawns did not respond more aggressively.
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44 .So the third hypothesis,
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45 .what\'s called reciprocal altruism.
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46 .Now, altruism has a very specific meaning in the world of animal behavior.
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47 .Simply put, it means that the behavior of one animal benefits others
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48 .at potential cost to itself,
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49 .which clearly describes what\'s happening here
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50 .and reciprocal altruism,
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51 .that\'s when animals do favors for each other.
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52 .One animal will do something to help another,
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53 .like share food,
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54 .expecting that it will someday be on the receiving end
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55 .a mother mule deer then might endanger herself to help others,
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56 .so that those others might later on protect her,
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57 .or, in this case, her fawn.
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58 .But theoretically, it only makes sense for her to help individuals that can be relied on to reciprocate,
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59 .to help her out in a similar situation.
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60 .So the rule about reciprocal altruism is
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61 .that an animal has to be able to recognize who is helping
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62 .Remember, though, that a mule deer cannot seem to identify the cry of its own species,
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63 .much less of its own offspring.
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64 .So why do mule deer choose to protect the young of others?
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65 .Or is this the wrong question to ask?
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66 .Maybe they\'re just sort of programmed to react mindlessly to any predatory threat
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67 .without stopping to consider whether it\'s their own offspring or others that they\'re protecting.
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68 .In any case, we\'ll need more evidence to figure out just how altruism is involved here,
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69 .and that will require a good deal more research.
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