  A comparison between the observed O-type star and the WR star populations and
the theoretically predicted ones depends on the effects of stellar wind mass
loss during various phases and rotation on stellar evolution and, last not
least, on the effects of binaries. Obviously, both populations depend on the
massive star formation rate. In the present paper we show that the rate in the
Solar Neighbourhood is fluctuating on a timescale which is smaller than the
evolutionary timescale of a massive star. We demonstrate that this fluctuating
behaviour affects both population enormously, in such a way that a comparison
between observations and theoretical prediction to test stellar evolutionary
models is ambiguous.
