  Mutualistic networks have been shown to involve complex patterns of
interactions among animal and plant species. The architecture of these webs
seems to pervade some of their robust and fragile behaviour. Recent work
indicates that there is a strong correlation between the patterning of
animal-plant interactions and their phylogenetic organisation. Here we show
that such pattern and other reported regularities from mutualistic webs can be
properly explained by means of a very simple model of speciation and
divergence. This model also predicts a co-extinction dynamics under species
loss consistent with the presence of an evolutionary signal. The agreement
between observed and model networks suggests that some patterns displayed by
real mutualistic webs might actually represent evolutionary spandrels.
