Philosopher: To explain the causes of cultural phenomena, a social scientist needs data about several societies: one cannot be sure, for example, that a given political structure is brought about only by certain ecological or climatic factors unless one knows that there are no similarly structured societies not subject to those factors, and no societies that, though subject to those factors, are not so structured.
Conclusion
In order to determine the causes of cultural phenomena, you need to have data from multiple societies.
Evidence
If you didn't have data from lots of societies, you wouldn't be able to look at how strongly correlated certain ecological / climatic factors are with certain structural features of society.
(The more data points you have, the more you can see whether certain structures co-varied with certain climatic/ecological factors)
Evaluate
They're asking us about the first sentence, which is the main conclusion. Both the colon that proceeds it and the "for example" show us that it's being supported.
The support is just a complicated way of saying,
Goal
Look for something that sounds like Main Conclusion.