analysis of what is thought to be the last common protist
ancestor of the metazoans could provide evidence
for this hypothesis. On the basis of morphological and
molecular studies, it has been indicated that the
CHOANOFLAGELLATES might form a sister group of the
metazoans38,39. Recent studies in the choanoflagellate
Monosiga brevicollis identified the first receptor tyrosine
kinase found outside the metazoans, indicating that the
evolution of some signalling molecules might have preceded
multicellularity40. Future research in this species
might therefore help to provide a better picture of signalling
systems in unicellular eukaryotes and might provide
a link to the origin of the metazoans