Initial Observation

The initial observation is that zebras and some other animals have stripes.

Preliminary Conditions

There are six theories posed to explain why zebras have stripes:

A₁: Camouflage. Stripes protect zebras by blending in with branches or thickets.
A₂: Dazzle. Stripes protect by giving an illusion of motion.
A₃: Cooling. Stripes set up convection patterns to cool the skin.
A₄: Social Interactions. Stripes facilitate social interactions.
A₅: Protection From Flies. Stripes protect by hindering fly bites.
A₆: Stripes have been on horses from the beginning.

Assume all of these theories have merit, satisfying at least half of the criteria for a scientific theory (it will be required to show this starting with the next set of examples). Also, each of the theories could explain the initial observation (as described above).

Data

D₁: There is no correlation between the density of woodlands and having stripes.
D₂: Lions eat lots of zebras.
D₃: The size of social groups is not correlated with stripes.
D₄: Stripes are correlated with regions that have high fly populations (warm regions).
D₅: Flies in zebra zones carry diseases that are lethal to zebras.
D₆: Studies in North America show that flies can cause substantial blood loss and lower milk production.
D₇: There are supporting evidences that since at least Palaeolithic, horses have worn stripes.

Evaluation Chart

	Camouflage	Dazzle	Cooling	Social	Flies	From Beginning
D1	no	yes	yes	yes	yes	yes
D2	no	no	no	no	no	no
D3	yes	yes	yes	no	yes	yes
D4	no	no	yes	no	yes	no
D5	no	no	no	no	yes	no
D6	no	no	no	no	yes	no
D7	no	no	no	no	no	yes

Result

From this data (Camouflage - 1, Dazzle - 2, Cooling - 3, Social - 1, Flies - 5, From Beginning - 3), it would seem that protection from flies best explains why zebras have stripes.