54 | New Scientist | 24 August 2019
Far-sighted
On a safari holiday in Kenya, I
was stunned by our local guide’s
ability to see wildlife at a great
distance and spot things that I
could barely see with binoculars.
Does visual acuity vary between
human peoples?Stephen Rowe
Shepperton, Surrey, UK
I have witnessed the fantastic
visual abilities of safari guides
myself and I think there are other
factors at play than differences
between human peoples.
Firstly, the guides usually
know their patch intimately, so
are familiar with the favourite
spots of particular animals and
look for them there. Secondly,
the presence of an animal may
register as a visual anomaly in
an otherwise familiar scene.
I also believe that our visual
processing systems can be trained
through experience to respond
to particular shapes and colour
combinations. After many trips
to the Masai Mara wildlife reserve
in Kenya, I am much better at
spotting distant animals than
I was when I first visited.Lauren McMahon
Peterborough, Cambridgeshire, UK
Guides are likely to know where
animals are usually found at
certain times of the day. They also
look for characteristic movements
or signs that give away an animal’s
location, such as how fresh their
tracks are or the presence of birds
near kills. Their vision has become
accustomed to looking for slight
movements when scanning an
area slowly, whereas most people
would do a fast scan.Jane Monroe
Arcata, California, US
The guide has probably spent a
lot of time focusing on outdoor
scenes, while visitors are more
likely to be people who spend their
lives in front of computer screens
or with their noses in books.
Their eyes don’t consistently
need to focus on objects at greatdistances, unlike the guide’s.
Perhaps the questioner is short-
sighted. Myopia is increasingly
common in developed countries
as greater numbers of people
spend more and more time
working at desks and are
therefore focusing their vision
on objects less than an arm’s
length from their eyes. In fact,
short-sightedness increases
in populations as they adopt
urban lifestyles and stop using
their long-distance vision.
A safari guide presumably
spends relatively little time at
a desk, while the eyes of those
who largely work indoors have
adjusted to that lifestyle. For
an in-depth look at this issue,
read Daniel Lieberman’s book
The Story of the Human Body:
Evolution, health, and disease.Keith Noble
Townsville, Queensland, Australia
When working with Ngaanyatjarra
people in Australia’s Western
desert, I was amazed by their
ability to spot kangaroos andother game at a great distance.
I struggled to develop this
skill. Finally, a young man told me
I was trying too hard and that I
needed to “look through the trees”.
The way I understood this was that
I should engage my peripheral
vision to see the animals rather
than use determined staring –
and when I did this, hey presto,
there they were.
During a night drive
across remote sand tracks at
80 kilometres per hour, the same
man – who had been nodding off
in the passenger seat – suddenly
yelled “Stop!”, jumped from the
vehicle and ran off into the dunes.
He returned with a 3-metre-long
woma, or sand python.
When I asked him how he saw
it, he replied, “I didn’t. I saw its
tracks and knew it had just crossed
the road.” It made a nice lunch.Stephen Jorgenson-Murray
Frankfurt, Germany
Like the guide, experienced
birdwatchers use cues such as
size, movement, shape, behaviour,
habitat and even the time of day to
identify a species without needing
a clear view. The term that they
and other wildlife spotters use
for this collection of subtle clues
is the “jizz” of the animal.Richard Kerr
Newton Mearns,
East Renfrewshire, UK
In Zambia, a Zulu friend once
pointed out an utterly still brown
crocodile on a brown mudbank
nearly a kilometre away. He drew
our attention to it not because it
was there, but to explain why its
mouth was open. I suspect that his
eyes were able to easily recognise
things that were more common
in his life than they were in mine.
He also had a good eye for the
best ways to take his car between
tree trunks to avoid the roots and
for which parts of ditches were
safer to drive in than the dirt road.
Again, I think it was because of
what his eyes were accustomed
to assessing.Sneeze blindness
Why do our eyelids involuntarily
close when we sneeze? Is it to
stop our eyes from popping out?Andrew Gould
Canberra, ACT, Australia
As a photic sneezer – someone
who sneezes at bright light – I
sneeze a lot and I have done some
experiments on this. I can assure
you that it is entirely possible
to sneeze with your eyes wide
open and not have your eyeballs
pop out. ❚This week’s new questions
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