A long history of posts goes back to the notion that the proliferation
of so many neurotransmitters reflects "evolutionary garbage"
>> > As for the "evolutionary garbage" idea, I think what your prof
>> > meant is that there's always an ongoing process of mutation and
>> > among both neurotransmitters and receptors.
Fred Delcomyn's text, "Foundations of Neurobiology" (WH Freeman, 1998)
discusses this on page 179.
"The enormous variety of neurotransmitters presents an interesting
for neurobiologists -- what are they all for? ...Why then, are there
diferent neurotransmitters? It would seem that just a handful would be
to serve the needs of the nervous sytem. It could be a case of
accident, a matter of mutations in membrane proteins yielding
that respond to various chemical substances that nerves happen to
It is also possible that particular neurotransmitter systems evolved
different chemicals happened to best serve neurons that had specific
This is probably not the original source of the notion -- that
is not neat and tidy, that "efficiency" or "perfection" is often
not the result is commonplace in biology. And Delcomyn is
a comparative physiologist with just this biological perspective.