  Analyzing powers in inclusive pion production in high energy transversely
polarized proton-proton collisions are studied theoretically in the framework
of the quark recombination model. Calculations by assuming the SU(6)
spin-flavor symmetry for the nucleon structure disagree with the experiments.
We solve this difficulty by taking into account the %We overcome this
difficulty by taking into account the realistic spin distribution functions of
the nucleon, which differs from the SU(6) expectation at large $x$, %but
coincides with a perturbative QCD constraint on the ratio of the unpolarized
valence distributions, $u/d \to 5$ as $x \to 1$. We also discuss the kaon spin
asymmetry and find $A_N(K^+) = -A_N(K^0)$ in the polarized proton-proton
collisions at large $x_F$.
