The weak anthropic principle can be summed up as the belief that, were the universe not suitable for intelligent life, no inteliigent life would be around to question at all.

Anthropic principle, as terminology in reference to this idea, appears to have originated with Brandon Carter, in the 1970s. Anthropic, as used by Carter, referred to all intelligent life, and not merely humankind, as the technical definition of the word would lead one to believe. By his delineation, the weak anthropic principle applies only to distinct spaciotemporal areas around the observer in question, and not to the whole of the universe or multiverse. Any claims made about all possibility, or the universe/multiverse are not necessarily references to the strong anthropic principle, though they are generally treated as such. The problem that Carter faced in these instances is that, for any given writer, the delineation between "universe" and "spaciotemporal area" is almost entirely arbitrary, and two authors may be referring to the same thing while using different terminology.

This concept is often misrepresented by those who wish to prove or argue intelligent design of existence. The most common mistake is the assertion that the observation that life exists proves that the universe/multiverse was designed to harbor life. As described, Carter's anthropic principle does not require that any form of deity exist, or that there be intelligence behind existence.

See also:
Strong Anthropic Principle
Special and Inevitable Anthropic Principle