# Drake's Equation Question Set: on what fraction of habitable planets with life does intelligence evolve?

This is the fifth question in a series estimating input parameters for Drake's equation, inspired by a recent paper, on the Fermi paradox.

The first question in the series, with more explanation, is here

The model in question uses probability distributions over seven input parameters.

In this case we will be addressing the fifth parameter in Drake's Equation, $f_i$. It is the fraction of life-bearing planets on which intelligent life emerges. This is pretty ill-defined but for our purposes we shall define intelligent life as a type capable of (a) symbolic representation and communication of a description of actions and objects, i.e. language, and (b) use of tools. Under this definition on Earth Humans would count as well as probably several type of nonhuman primates, many cetaceans, and some types of birds.

There being no obvious source of a hard lower-limit on this parameter we set that to $10^{-20}$, but with an open border. We'll count multiple intelligent species on a planet as a single one.

The resolution to this question will be the scientific consensus 100 years from now, regardless of any remaining uncertainty.

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