16 | New Scientist | 10 August 2019Marine biologyHumans are great
at smelling cheeseSMELL that? If it is cheesy, sweaty
or sweet, you might be more likely
to sense an odour. Humans have
evolved a lot of smell receptors for
these scents, probably to help us
choose which foods to eat.
Luis Saraiva at Sidra Medicine
in Doha, Qatar, and his colleagues
looked at smell receptors in mice
and people. To do this, they
analysed a patch of neurons that
contain smell receptors. This areaYellow glasses don’t
improve night visionWEARING yellow glasses while
driving at night might make you
think you are seeing better, but
tests in a simulator have shown
that drivers wearing them don’t
spot pedestrians any faster than
those wearing clear glasses.
In reality, the yellow glasses
reduce the amount of light
entering the eye and thus what
people can see at night, says Alex
Hwang of Harvard Medical School.
“It’s like wearing sunglasses
during the night-time,” he says.
Yellow glasses designed to
reduce the glare of the headlights
of oncoming vehicles have been
sold since the 1950s. The idea
behind them is that because
blue light gets scattered more,
filtering it out reduces glare.
Such glasses are often advertised
as improving night vision,
and eye-care professionals
commonly advise their use.Driving OlfactionTURTLE embryos seem to influence
their eventual sex by shifting
around within their eggs and
seeking out hot or cool spots.
In some turtles, cooler eggs
produce males and warmer ones
produce females. That is a concern,
because climate change could
result in one-sided sex ratios. Now
work suggests that turtles may
have some ability to adapt to this.
“Embryos can detect temperature
differentials within the egg and
move to the optimum position,”
says Rick Shine at Macquarie
University in Australia.
He and his colleagues measured
the temperatures of the eggs of a
type of freshwater turtle, Mauremys
reevesii, in outdoor nests. The
temperature was higher at one end
of each egg than at the other, with
a maximum difference of 4.7°C.“The temperature difference
needed to shift from ‘develop as
a male’ to ‘develop as a female’ is
only about 1°C,” says Shine. There
is enough temperature difference
within an egg for an embryo to
change its temperature that much.
Lab tests showed that embryos
that couldn’t sense temperature
stayed in the middle of the egg and
either all males or females hatched,
depending on the incubation
temperature. Those that could
sense it moved up to 6 millimetres,
and about half were of each sex
(Current Biology, doi.org/c82g).
Fredric Janzen at Iowa State
University says it is unlikely that
embryos move like this. The yolk
would be in the way, and embryos
would have to move twice a day to
cope with temperature fluctuations,
he says. Chelsea WhyteTurtle embryos may change
sex by moving in the egg
is some 2.5 square centimetres in
humans and sits between the eyes
at the top of the nasal cavity.
The team extracted mRNA from
each sample. These molecules
help genes to make proteins,
so levels of them indicate which
genes were “switched on”, as well
as their relative abundance.
Both species have more
receptors for odours that smell
like rancid milk or cheese, sulphur
or sweat, or are particularly sweet
or spicy-smelling, like vanilla
or clove than for other smells
(Science Advances, doi.org/c82n).
These help us make decisions
about which foods are safe to eat,
says Saraiva. But in mice, the
chemicals also act as pheromones
that can influence their behaviour,
such as scents that attract mates.
We have lots of receptors
for chemicals also found in
bodily fluids like breast milk
and vaginal fluid, but there
is no evidence these act as
pheromones in humans,
says Saraiva. Jessica HamzelouTo see how these glasses might
affect the performance of drivers
at night, Hwang’s team kitted out
a driving simulator with high-
intensity LEDs that can match the
brightness of vehicle headlights.
Twenty-two people aged
between 21 and 80 each did
eight driving sessions of about
10 minutes in the simulator. They
sounded the horn when they saw
a pedestrian crossing the road.
People wearing yellow
glasses – the study used three
makes sold commercially –
responded a fraction of a second
later than those wearing clear
spectacles (JAMA Ophthalmology,
doi.org/c82j). The difference
wasn’t statistically significant,
but Hwang thinks it would be
if the study were repeated with
more participants.
The volunteers all thought the
glasses did help, though, saying the
night scenes looked brighter. That
means wearing yellow glasses
may make people overconfident,
Hwang says. Michael Le PageMODOKI MASUDA/NATURE PRODUCTION/MINDEN PICTURES
AGE FOTOSTOCK/ALAMY STOCK PHOTONews In brief