  Based on well-known properties of semi-classical black holes, we show that
weakly-coupled string theory can be viewed as a theory of N = 1/g_s^2 particle
species. This statement is a string theoretic realization of the fact that the
fundamental scale in any consistent D-dimensional theory of gravity is not the
Planck length l_D, but rather the species scale L_N = N^1/(D-2) l_D. Using this
fact, we derive the bound on semi-classical black hole entropy in any
consistent theory of gravity as S > N, which when applied to string theory
provides additional evidence for the former relation. This counting also shows
that the Bekenstein-Hawking entropy can be viewed as the entanglement entropy,
without encountering any puzzle of species. We demonstrate that the counting of
species extends to the M-theory limit. The role of the species scale is now
played by the eleven-dimensional Planck length, beyond which resolution of
distances is gravitationally-impossible. The conclusion is, that string theory
is a theory of species and gets replaced by a pure gravitational theory in the
limit when species become strongly coupled and decouple.
