7 November 2020 | New Scientist | 55Tom Gauld
for New Scientist
Answers
Geoff Piltz
Eskdalemuir, Dumfries
and Galloway, UK
I have seen a quadruple rainbow
on the waterfront at Liverpool, UK.
There was a double rainbow with
a taller pair of rainbows above it.
This second set started at the same
apparent origins as the first set,
but extended higher into the sky.
After consideration, I have come
to the conclusion that the first set
was created by light directly from
the sun, whereas the second set
was made by light reflected off
the river Mersey.
Looking back
Why hasn’t evolution given us eyes
in the back of our head or rear-view
mirrors? (continued)
Eric Anderson
Wickford, Rhode Island, US
While the previous answers to
this question were good, they
missed something.
Many vertebrates have a third
or “parietal” eye at the top of
their head, including some lizards,
frogs, salamanders and sharks.
This eye doesn’t form images,
but it is sensitive to light and dark.
The parietal eye may even have
developed from a more functional
eye or pair of eyes that would have
allowed true sight overhead or
even to the rear.
The human pineal gland,
which produces melatonin in
response to light signals from
our eyes, is thought to have
originated from the parietal eyes
of the non-mammalian ancestor
that we evolved from.
Depending on how an eye is
defined, it could be that scorpion
fluorescence serves as a basic eye.
It seems that a scorpion’s glow is
a by-product of its exoskeleton’s
ability to sense light – or “see” –
hinting that it can tell whether it
has left any part of itself visible topredators when it takes
cover during the day.Peter Jacobsen
Davis, California, US
One species of swallowtail
butterfly has rear vision. The
male has photoreceptors on its
penis that help it position itself
for mating. The female can also
sense light with its genitals,
probably to help her lay eggs
in the right place.Mike Follows
Sutton Coldfield,
West Midlands, UK
Humans have few predators and
can use our hearing and the eyes
of fellow hunter-gatherers to
detect many of them, so there is
little evolutionary advantage to
expending energy in order to have
eyes in the backs of our heads.
Evolution doesn’t always find
the perfect fit to the environment.
But if rearward vision were
advantageous, then I think it
would be more likely that we
would have adapted to turn our
heads 180 degrees like owls. ❚Quick quiz #76
Answer1 A Dyson sphere
2 Seven
3 The Mesozoic era
4 Chromatography
5 QuinineCryptic crossword
#43 AnswersACROSS 1 Dog star, 5 Pique,
8 Charm, 9 Bus fare, 10 Faintly,
11 Ankle, 12 Format, 13 Despot,
16 Anode, 18 Lithium, 20 Braille,
21 Meant, 22 Shear, 23 East EndDOWN 1 Decaf, 2 Glazier, 3 Time
traveller, 4 Ribeye, 5 Postage
stamps, 6 Quark, 7 Element,
12 Flambes, 14 Primate,
15 Allele, 17 Orate, 19 Muted#83 Albatross^
SolutionIf we call the height of the mast
3H, the stone climbed H above
that to be 4H above the ground at
its peak. A parabola is a “square”
function, so the height increases
with the square of the horizontal
distance. If the top of the stone’s
path was d from the mast,
Pugwash was 2d from the
peak. The flight of the stone is
symmetrical around the peak,
so if the peak is d from the mast,
it is also d from the point of
impact. So the point of impact
is d from the peak, 2d from the
mast and 3d from Pugwash, and
the stone was travelling at 3/2 or
1.5 times the horizontal speed
of the albatross, or 15 knots.“ Some swallowtail
butterflies have rear
vision. The male can
sense light with its
penis to help find the
right mating position”H4HPugwashdMastImpact