  We present a critical analysis of the observational constraints on, and of
the theoretical modeling of, aspects of cosmic ray (CR) generation and
propagation in the Galaxy, which are relevant for the interpretation of recent
positron and anti-proton measurements. We give simple, analytic, model
independent expressions for the secondary pbar flux, and an upper limit for the
secondary e+ flux, obtained by neglecting e+ radiative losses, e+/(e+ +
e-)<0.2\pm0.1 up to ~300 GeV. These expressions are completely determined by
the rigidity dependent grammage, which is measured from stable CR secondaries
up to ~150 GeV/nuc, and by nuclear cross sections measured in the laboratory.
pbar and e+ measurements, available up to ~100 GeV, are consistent with these
estimates, implying that there is no need for new, non-secondary, pbar or e+
sources. The radiative loss suppression factor f_{s,e+} of the e+ flux depends
on the e+ propagation in the Galaxy, which is not understood theoretically. A
rough, model independent estimate of f_{s,e+} 1/3 can be obtained at a single
energy, E\sim20 GeV, from unstable secondary decay and is found to be
consistent with e+ measurements, including the positron fraction measured by
PAMELA. We show that specific detailed models, that agree with compositional CR
data, agree with our simple expressions for the e+ and pbar flux, and that the
claims that the positron fraction measured by PAMELA requires new primary e+
sources are based on assumptions, that are not supported by observations. If
PAMELA results are correct, they suggest that f_{s,e+} is slightly increasing
with energy, which provides an interesting constraint on CR propagation models.
We argue that measurements of the e+ to pbar ratio are more useful for
challenging secondary production models than the positron fraction.
