  We reanalyse hyperon beta decay data to extract the corresponding F and D
values. We show that flavour symmetry breaking effects lead naturally to a
reduction of the $F/D$ ratio. For proton and neutron our analyses suggests $F/D
= 0.49 \pm 0.08$ instead of $F/D = 0.575 \pm 0.016$ which is generally used to
analyse the spin data. Our smaller $F/D$ value allows to fullfil the
Ellis--Jaffe sum rule implying an unpolarized $s\bar s$-sea.
