You must describe how each of your hypotheses explain the reduced amount of hair; i.e., what causes an increase in fitness for individuals with less hair than others.
Now you have 4 hypotheses (+ a non-selective one if we are being complete) for a total of 5. Create an experiment, observation or comparative study to test one of these hypotheses. Clearly describe your study subjects and conditions, the data that you will collect (i.e., what values are measured), and which observable patterns would support your hypothesis and which would not.
Hypothesis 1: Humans are hairless because of male preference for less and less hairy females
Hypothesis 2: Humans are hairless because of thermoregulation on the African savannah
Hypothesis 5: There is no selective reason as to why humans are hairless.
So need to create hypothesis 3 and 4. For one of these two hypothesis (that you created for relative hairlessness of humans) create an experiment, observation or comparative study to test hypothesis. As said by instructions.
