Sexual Selection: Mates, Relatives, and Animal Strategy

Science · Animals of the World · ages 12-13

Name ______________________ Date ____________

Which of these is the best example of a trait shaped by sexual selection?
- A cheetah's fast running speed
- A peacock's colorful, oversized tail feathers
- A camel's ability to store fat for the desert
What is sexual selection?
- Traits favored because they help an animal attract mates
- Traits favored because they help an animal escape predators
- Traits that appear randomly and don't affect survival at all
Worker bees can spread their genes even without having their own offspring, by protecting relatives that share those genes.
Circle one: True False
Over many generations, peahens kept picking males with slightly longer tails. What is most likely to happen to tail length over time?
- It keeps growing longer, even past what helps the bird survive
- It shrinks back down to the most practical length
- It stays exactly the same every generation
A meerkat stands guard and risks being caught by an eagle so the rest of the group can hide. Which idea best explains why this behavior can still spread the meerkat's genes?
- The meerkat is trying to escape competition from its own group
- The meerkat wants to attract a mate by acting brave
- Kin selection: protecting close relatives protects shared genes
The chart shows average points per game in a hawk-dove contest. Based on the chart, why doesn't constant fighting (hawk vs hawk) win out?
- Fighting always gives the highest score no matter what
- All-out fighting causes injuries that lower the average score
- Sharing calmly (dove vs dove) always loses to fighting
Hamilton's rule says a behavior is favored when relatedness times benefit is greater than cost (r x B > C). A meerkat is related to its group by 0.5. Guarding gives the group a benefit of 10 points, at a cost of 4 points to the meerkat. What is r x B?
Answer: ______________
A student says: 'Animals can't really play or feel emotions, that's just what it looks like to us.' What would a cognitive ethologist say?
- Only humans can ever be studied scientifically for emotion
- The student is completely correct, animals behave like simple robots
- There is real evidence, like brain activity and consistent behavior patterns, that many animals do show play and emotion

Answer key

For grown-ups. Fold this page away before handing over the rest.

Sexual Selection: Mates, Relatives, and Animal Strategy W1-mt_YNrrNE23dZ-s1

A peacock's colorful, oversized tail feathers · A peacock's tail doesn't help it survive better, it helps it attract mates, which is sexual selection at work.
Traits favored because they help an animal attract mates · Sexual selection favors traits that help an animal attract mates, separate from traits that just help it survive.
True · A worker bee shares genes with her sisters and the queen, so protecting them protects copies of her own genes too.
It keeps growing longer, even past what helps the bird survive · Since peahens keep favoring longer tails, the trait and the preference for it reinforce each other in a runaway spiral.
Kin selection: protecting close relatives protects shared genes · Meerkats share genes with their group, so Hamilton's rule says the risk is worth it when enough relatives are protected.
All-out fighting causes injuries that lower the average score · Hawk vs hawk contests often end in injury, which drags the average score down even though hawks look tougher.
5 · 0.5 x 10 = 5, and since 5 is greater than the cost of 4, Hamilton's rule predicts guarding will be favored.
There is real evidence, like brain activity and consistent behavior patterns, that many animals do show play and emotion · Ethologists look for real evidence, like brain patterns or repeated behavior, instead of assuming animals can't feel or think.