  The observed luminosity distributions of X-ray sources indicate the presence
of several populations of X-ray binaries in the nearby galaxies. Each
population has its formation and evolutionary history, depending on the host
environment. The features seen in the log N($>$S) -- log S curves for different
types of galaxies and for different galactic components can be reproduced by a
birth-death model, in which the lifespans of the binaries are inversely
proportional to their X-ray brightness. Conversely, the dynamical history of a
galaxy can be inferred from the luminosity distributions of its X-ray binary
populations.
