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There
has obviously been a strong selective pressure on protist cells to keep
together for their mutual advantage that lead ultimately to the
evolution of metazoans. The slime moulds, famously exemplified by Dictyostelium
discoideum are a half way house, most often living as distinct
individual amoeba but occasionally coming together for sexual purposes
and to disperse the progeny. The formation of the Dictyostelium
amoebae to produce the fruiting body does involve the death of a
significant proportion of these amoeba so this could be looked upon as
kin selection for the greater good of the species. Is there any
such indication of kin selection in amoebae? The answer is
equivacal! in some species canabolism is regularly observed, a
distinctly non-kin selecting activity, yet in others there is evidence
for apoptosis. This is strong evidence for kin selection as it is
difficult to imagine why an amoebae that essentially does its own thing
would evolve the dangerous ability to kill itself if this mechanism was
not for the good of the whole species. (see amoeba and apoptosis). |
