we have eyes for vision we have ears for
hearing
but we have no organ that we know of
that's involved in magnetoreception it's
a complete mystery
for decades researchers have tried to
answer a simple
question with a remarkably complex
answer
how do birds find their way i had never
thought
that i would get to a place where we
would start
understanding the quantum mechanical
mechanism
that goes on inside the bird
[Music]
one of the greatest mysteries in sensory
biology
is how animals are able to sense the
earth's magnetic field and to use it to
navigate
researchers have shown that some animals
can indeed sense earth's magnetic field
using it to navigate but how birds like
the european robin detect such a weak
field
has long baffled biologists it's the
last sense
we effectively know nothing about and
the solution of this problem
i would say is the greatest holy grail
in sensory biology
and although the answer has remained
elusive researchers have put forward
theories that they hope
could explain this mystery over 40 years
ago in the late 1970s
a physicist first dreamt up the idea
that a light sensitive molecule
might be used by animals to sense the
earth's magnetic fields
this theory proposed that animals could
sense magnetic fields using a quantum
mechanical phenomenon
called radical pairs the radical pair
hypothesis suggests that you have a
light sensitive molecule
it absorbs light and in the end
you have a radical pair so two unpaired
electrons
the magnetic spins of this radical pair
can take on two states
both pointing in the same direction a
triplet state
or both pointing in opposite directions
a singlet state
the pair swings between these two states
but a magnetic
field tips the balance increasing the
likelihood of one of the two
and it's this change in the balance of
the lifetimes of the triplet state
relative to the singlet state
which is thought to be the basis of
magnetoreception
and there was only one class of
molecules
that people knew originally could
use light to generate radical pairs in
plants
and they were called cryptocrops so
henrik and his collaborators hunted for
these cryptochrome molecules
in birds and since cryptochromes need
light to work they searched specifically
in bird
eyes we found cryptochromes in the
isobirds and so did others
and then the big challenge was now well
how do you now
test whether quantum mechanic
electron spin based mechanisms goes on
inside the eye of a bird
the main barrier for the adoption of the
cryptochrome
hypothesis was that it was proposed by a
physicist
so the mechanisms involved were highly
quantum mechanical
very very difficult for biologists to to
understand
henrik and collaborators from biology
physics and quantum chemistry
have worked to shed light on this crypt
chrome hypothesis
we needed to have the molecule in
isolation to
actually measure things on it because
it's very very difficult to do it inside
the eye of a bird
we started trying to make cryptochromes
in 2004 and we now have 2021
at the moment we are the only ones who
have these molecules available
for testing and in oxford the groups are
the only ones who can measure such
molecule with the sensitivity needed
to see what we have found not only could
we show that the electrons
jump inside the molecule exactly as
predicted by the quantum chemists in
theory
we could also show that the
photochemistry
of that radical was actually
magnetically sensitive
now it's not a hypothesis that this
molecule is magnetically sensitive
we can see that it's magnetically
sensitive the team were also curious how
cryptochrome proteins compared between
birds that migrate
and birds that don't we then also made
cryptochromes from
an extreme non-migratory bird basically
the chicken
and it looks like the cryptochrome 4
from the migratory birds
are significantly more magnetically
sensitive than
the same molecule from a chicken
previous work has shown that birds
process magnetic field information
in the visual region of their brains
and so henrik and team members believe
birds may actually
see the earth's magnetic field so maybe
it's kind of a shadow on top of whatever
else you would be seeing as a bird
but what exactly the bird is seeing we
do not know because we cannot ask the
bird
but the puzzle isn't solved the team
have shown that cryptochromes are indeed
magnetically
sensitive but they haven't yet proven
that these proteins
are the critical ingredient in
magnetosensing in birds
the advances that the authors have made
in this study
has brought us a long way to
understanding how magnetoreception works
there's no question that the study was a
spectacular piece of science
but because this is a laboratory study
it's not a
study which has been performed on living
animals it's still
no actual proof that cryptochromes in
general
are actually used in magnetosensing we
are of course going to try to get closer
to the natural situation inside the eye
of the bird
things like that would have been utopia
before you could actually make
the molecule in isolation and we are
very excited about the possibilities
there
i think having studied quantum mechanics
myself years and years ago
i would never have realized then or even
believed i think that
it would be possible that quantum
mechanical effects could be
actually housed within the eye of a bird
that is a huge surprise
and that's nothing we learned in quantum
mechanics when i was young
you