so this has been a big question is - how did vocal learning circuits evolve to
answer that question we also need to understand what are these vocal learning
circuits well only a few species have them us humans these songbirds a few
others I'll tell you about in a minute and they all have a similar brain
pathway that we and others discovered in our fore brain that controls the muscles
that produces sound and what's interesting is in all the species that
we discovered this vocal learning pathway it's embedded in another pathway
that all species have learning how to control our movements and wings for
flying learning how to walk and so forth so this led to a new theory called the
motor theory of vocal learning origin where we think that the speech vocal
learning circuits in our brain and these birds evolved by duplicating the pathway
that controls other body parts and now hooking it up to the voice instead of
learning how to walk learning how to talk so basically the vocal learning
circuit is a motor learning circuit and in terms of who has it and why so few
species well like I said us humans but there are a few other mammals elephants
dolphins and whales well they call pinnipeds those of like seals and
walruses and also of bats in the ultrasonic range that we can't hear and
there are only three groups of birds these songbirds like the zebra finch
hummingbirds and parrots you just heard along to learn a song and what that guy
is trying to do is to sing to the females to say my song sounds sexy be
with me and we think that's one of the things that selecting for vocal learning
but why so few species well I think that predators are selecting against it if
you evolve this thing to keep attention to the opposite sex
you're also keeping attention to the Predators out there
and you could be eaten but the ones like us like humans and dolphins whales the
top predators can evade these other ones the common ancestor of these birds and
songbirds and parrots was a apex predator so that's one theory there are
many other theories it's a why so few species have it may be the ones that
have the bigger brains songbirds have a bigger brain than other
species humans have a bigger brain than other mammal species another is
something about the social interaction of the species creates this environment
for the genetic mechanisms to cause a brain circuit to evolve more social
complex behaviors but I like the predator Hut and the sexual selection
hypothesis is the best it makes more sense of what we're seeing like these
guys seem to attract the female but there is one more new theory that we've
come up with that explains both of these questions about where the circuits for
vocal leaning came from and why so few species we call it the Continuum
Hypothesis of vocal learning and the discovery for that came from studying
mice we found that mice actually have a rudimentary brain circuit that we find
in humans for speech in song birds for song and they have some rudimentary
abilities to change their songs that the females like and so what we think could
be happening is that maybe it's not a black or white world the haves and the
have-nots but it's a continuum like turning up the dial or turning down the
dial to make the behavior more complex or less complex and in humans we're at
this end of the continuum mice and some other species frogs at this end and
other species in between so we're testing this continuum hypothesis and
how we're testing it well if mice are somewhere in the middle or even yeah a
little bit at the other end of the continuum can we take the human genes
put it in a mouse brain in the mouse cells in the mouse genome and push that
Mouse to dial up the dial along that continuum and to get it to be more like
a song even us