Choosing similar friends can have a rationale. Assessing the survivability of an environment can be risky (if an environment turns out to be deadly, for instance, it might be too late by the time you found out), so humans have evolved the desire to associate with similar individuals as a way to perform this function efficiently. This is especially useful to a species that lives in so many different sorts of environments. However, the carrying capacity of a given environment ____________________. If resources are very limited, the individuals who live in a particular place cannot all do the exact same thing (for example, if there are few trees, people cannot all live in tree houses, or if mangoes are in short supply, people cannot all live solely on a diet of mangoes). A rational strategy would therefore sometimes be to avoid similar members of one’s species.