Current issues concerning the nature of ancestry and homology are disc
ussed with reference to the evolutionary origin of the tetrapod limb.
Homologies are argued to be complex conjectural inferences dependant u
pon a pre-existing phylogenetic analysis and a theoretical model of th
e evolutionary development of ontogenetic information. Ancestral condi
tions are inferred primarily from character (synapomorphy/homology) di
stributions within phylogeny, because of the deficiencies of palaeonto
logical data. Recent analyses of tetrapod limb ontogeny, and the diver
se, earliest morphologies known from the fossil record, are inconsiste
nt with typological concepts such as fixed ancestral patterns or baupl
ans, emphasising the incompatibility of these with evolutionary contin
uity. The evolutionary origin of the tetrapod limb is also examined in
the light of its recent discussion in developmental genetics. While t
his field promises to reveal more of the fundamental ontogenetic conte
nt of homology (identity), at present it is concerned mostly with the
abstraction of a new set of types, rather than investigating diversity
and change.