Kind: captions
Language: en
are you the person in the group who is
always getting bitten by mosquitoes
because I certainly am and science has
shown that this is a thing that
mosquitoes are more attractive to some
people than others and the reason for
that is at least partially genetic which
is why this video is supported by 23 and
me a company that reads sections of your
genetic code and then helps you
understand what's in there now they've
actually been involved in some research
that has identified particular spots on
your DNA that make you more or less
likely to be attractive to mosquitoes
and in this video I want to put that to
the test so I flew to New Mexico State
University to meet Mosquito Man
Professor IMO Hansen
hello we have a collection of lab
strains here he maintains colonies of
many different species of mosquitoes and
one exotic strain he actually feeds with
his own blood no no I'm serious these
ones are made from my blood really yes
absolutely yeah
them I can't ask my students you know
that would be a whole a nightmare
getting permissions how do you blood
feed them
well with just sticking your arms I just
put my arm in there and wait
is it psychologically itchy or no it is
really itchy yeah and I'm getting I mean
25 bites or so right now
mosquitoes need our blood proteins to
make their eggs so only the female
mosquitoes bite the eggs hatch into
these Wrigley larvae which develop into
pupae before becoming flying adult
mosquitoes then they once again seek out
vertebrate blood to make more eggs the
whole life cycle takes just two weeks
but what I wanted to know is am I a
desirable Target
how can we figure out if I'm attractive
to mosquitoes okay we have a white tube
basically which has a holding chamber we
put the mosquitoes down here there's a
little fan reducing a draft something
like four meters per second we're gonna
insert a bait into one of these Chambers
and the green or the yellow one so by
bait you're saying me yes you exactly
you put your hand in there would be good
if you would rub your hand first so uh
if you're sweating yes
exactly it is
almost feeds exclusively on humans they
are really specialized on biting humans
that's good to know yeah
there's 20 mosquitoes in the holding
chamber and they're going to decide
whether to come and find me or go down
the other side and they find nothing
right we're releasing the mosquitoes
yeah I see them coming oh he's chosen
wrong
do you see that
man you are attractive I'm really sorry
you are strong attractant to mosquitoes
they all went in your direction none of
them went the other way yes
this is amazing oh there's one I did not
I did not expect to have such a strong
response like
you see all those mosquitoes
this type of test was actually used to
discover that the basis for our
attractiveness to mosquitoes is at least
partially genetic researchers recruited
18 pairs of identical female twins and
19 pairs of non-identical or fraternal
female twins then they used the y-tube
test to evaluate the mosquito
attractiveness of each individual
measured by the fraction of mosquitoes
who correctly flew to the arm of the
tube where the twin was standing what
scientists found is that the mosquito
attractiveness of twins is correlated
that is the more attractive you are to
mosquitoes the more likely your twin is
too but that's not all that surprising
and could be caused by environmental
factors or a common diet but comparing
identical twins to fraternal twins
revealed the correlation was higher for
identical twins
strongly suggests genetics influence how
attractive you are to mosquitoes since
the identical twins share more of the
same genes than fraternal twins this
explains why their mosquito
attractiveness would be more closely
correlated if it really is genetics that
determines how much mosquitoes like you
with that last test I was clearly
attractive to these mosquitoes Yes
except we weren't comparing me to any
other human we were just comparing me to
a control exactly yes no human so what
if we compare myself with my wife Raquel
normally I get bitten and she doesn't
Okay so this should be a good test Maybe
to see whether under lab conditions we
can reproduce here uh we'll we'll
produce our anecdotal findings exactly
anecdotal evidence yeah a little once
again
preparing
okay hands in position yeah yeah see
they they actually start to wake up they
smelled some something something's going
on here
okay what are we saying
whoa
I'm getting a good amount over here but
so are you
let's see I think I'm getting more you
it looks to me like you got three okay
Wanna Stop The Experiment right now all
right
okay now let's count I think it's seven
on your side here
five in the holding five on the holding
and quite a few on your side
so who got spitting I get bit you get
bitten in reality we would repeat this
experiment maybe eight times or so right
and switching you guys around but um I
think
this is
a good way to show how how this works
okay so that result was not particularly
scientifically rigorous but it did
reproduce our experience in the wild
which is that I am much more attractive
well at least when it comes to
mosquitoes
um than Raquel but the question is I
guess does this come down to our
genetics yeah so we spat into some tubes
and sent them off to be tested right and
we were interested in seven particular
locations on our DNA which were located
in a 2017 study that involved 23 and me
so the way 23andMe works is when you
sign up you can opt in to be part of
research and 16 000 people agreed to be
part of this study and rate their
perceived attractiveness to mosquitoes
so then what the scientist did was a
genome-wide Association study that is
they looked at all the DNA of all of
those participants and tried to see if
there were commonalities amongst the
people who said they were attractive
mosquitoes and that were different to
the people who said they weren't
attractive to mosquitoes and they
identified seven particular locations on
the DNA seven single letter changes
which seem to be associated with
different levels of attractiveness to
mosquitoes so we have our results back
and do you want to see them I do I do
I'm very curious all right
um let's pull it up here okay so of the
seven locations that are related to
Mosquito attractiveness it turns out we
have the identical DNA at four of them
so you can rule those out which leaves
only three areas where we actually have
differing DNA so at the first location
you have one copy of a letter change
which actually makes you significantly
protected from mosquitoes oh no yeah
it's associated with decreased
attractive to mosquitoes I do not have
any letter changes at that location uh
now at the second location where we
differ I have a letter change compared
to you that makes me uh less attractive
to mosquitoes so more protected
interesting if you look at the
significance of those two letter changes
yours is about twice as significant okay
than mine but still we both have a
protective letter switch so in the last
snip we actually differ significantly
and I have two copies of a variant that
makes me more attractive to mosquitoes
this was the only snip which was
associated with being more attractive to
mosquitoes and I have two copies of that
change and you have no copies of that
change so let me know if that makes
sense so overall I would say our
genetics really adds up here and of
course we can't say that this proves
that it is right but it is definitely
consistent with these Snips actually
being associated with your
attractiveness to mosquitoes and that
sort of borne out by our experience so
cool
now it's unclear exactly how these
genetic changes might make us more or
less attractive to mosquitoes but it's
likely that it has something to do with
the odor or the volatile chemicals that
our bodies give off and due to the
microbiome the bacteria on our skin one
of the main signals that mosquitoes like
to follow is carbon dioxide so that
means if you have a higher metabolism or
if you've just been exercising or if
you're a bigger person or even if you're
pregnant you are more likely to attract
mosquitoes but mosquitoes are also
attracted to some other volatiles that
we give off things like lactic acid
acetone and ammonia but scientists have
also found some chemicals that repel or
appear to impair mosquitoes ability to
find us those chemicals we naturally
give off are octanal nonanal decanal and
six-methyl 5-heptin to own so why is
this important well the researchers
estimate that our attractiveness to
mosquitoes is about as hereditary as
height or IQ that is to say genetics
play a significant role here so
understanding that relationship is
really important especially when you
consider that of all the animals
mosquitoes have the greatest impact on
human health are mosquitoes the worst
animal of all time for humans absolutely
absolutely there's no question about
that malaria has killed more people than
people have killed people they are the
most dangerous animal in the world
by some estimates mosquitoes have killed
more than half of the humans who have
ever lived now that estimate has been
debated and is likely too high but even
so this year over a million people will
die of mosquito-borne illnesses so if
not half certainly a significant number
of humans have died due to mosquitoes
probably more than any other single
cause which led me to wonder do you
think humans may have evolved this trait
to smell worse to mosquitoes as an
adaptation to avoid the diseases or is
it just by accident that some people are
less attractive to mosquitoes than
others
that is a really good question
and while we're on the subject of
evolution consider this if you ever
contract malaria it actually changes
your body chemistry to make you produce
an odor that makes you more attractive
to mosquitoes think about that the
malaria parasite has evolved so that
when it's in its host it makes the host
more attractive to mosquitoes mosquitoes
are the thing that transmit malaria
it's phenomenal I mean evolution is
incredible
this episode of veritasium is supported
by 23 and me a company whose name comes
from the fact that humans have 23 pairs
of chromosomes and the point of the
company is to help people understand
what's written in your chromosomes now
at the minute you can't get access to
the mosquito attractiveness test but
maybe one day in the future you will be
able to right now you can access tons of
information about your physical traits
about aspects of your health and about
where your DNA and I guess you come from
so I thought I would share my results
with you I come from all over the world
as you can see from the map but
significantly more from Europe about 95
European you can drill down into that
and see that I'm largely British and
Irish and French and German with a bit
of Scandinavian what's interesting to me
is there's a 3.3 percent South Asian
which is something I think my family
suspected but didn't know for sure so
it's interesting the types of
information you can find out which is
stored in your DNA so if you want to
find out about the information in your
DNA you can go to 23andme.com veritasium
so I want to thank 23andMe for
supporting veritasium and I want to
thank you for watching