Why buy the cow if you can get the milk for free... We have obviously evolved
due to an advantage NOT to have autotrophic qualities. Why grow our own limbs
and vegetation tissue if all we have to do is harvest it off of the multitude
of organisms around us. We may be considered different organisms than a plant
(and rightly so) but we could not obviously exist without them. So looking
at the larger picture our ecosystem is a type of "organism". So maybe we as
an ecosystem do have the exact advantage brought up earlier :)
My teachings this sester include Euglena, the mobile autotrophic protist.
I think that is about as close as you will come to a plant-like animal at
least that I have seen.