14 | New Scientist | 7 December 2019News
A CHANCE discovery in
a 90-year-old German
book may have completely
overturned our understanding
of how crystals grow.
The defining feature of a
crystal is that it is composed
of a pattern of atoms that repeats
in all directions with perfect
symmetry. This neat structure
makes it possible to diffract X-rays
through crystals to reveal the
pattern inside, a technique
instrumental in understanding
the atomic structure of many
important drugs, like penicillin.
But X-ray diffraction is very
difficult to apply to small crystals,
so we have long been unsure
of what crystals look like when
they begin to grow.
Bart Kahr at New York
University has been trying to
solve this puzzle since 2007, whenhe came across a book published
in 1929 called “Gedrillte” Kristalle,
which describes many tiny
crystals with helical shapes.
Gedrillte is German for “drilled”,
and so was perhaps meant
to signify how the crystals
resembled helical drill bits.
This was a big surprise to Kahr.
Crystals tend to have straight sides
and geometric shapes. “I asked
everybody in the world about
this,” says Kahr. “Nobody knew
what the heck I was talking about.”
He began investigating
and soon confirmed that one
type of crystal could grow in a
twist. Over the past decade, he
and his colleague Alexander
Shtukenberg have found about
150 examples, and Kahr says
another 100 or so have also been
reported by other scientists.A strange twist to
how crystals form
ChemistryJoshua HowgegoHe has now found twisting in
common over-the-counter drugs,
including aspirin, paracetamol
and ibuprofen (Crystal Growth &
Design, doi.org/df8g).
“The point was to emphasise
how something so common can be
so poorly appreciated,” says Kahr.
His work has been “really
great at focusing on the very thin,
hair-like crystals that nobody
could solve and that tended to
be ignored”, says Sally Price at
University College London.
“I find it fascinating that
such twisted structures may
be a precursor to non-twisted
crystals,” says Matthew Fuchter
at Imperial College London.
“The fact a given structure grows
twisted only to then unwind as
it becomes larger is amazing.”
So how do crystals go from
being twisted when they are tiny,
to straight when they are larger?
This is an “intellectual chasm”,
says Kahr, and one that he is
now starting to investigate.
“Twisting is surely teaching
us what is a crystal, especially in
the early stages of growth, and
that is foundational, so who
knows what it could eventually
explain,” says Kahr. ❚BY PRACTISING new songs in
their wintering grounds, adult
male thrush nightingales may be
better prepared to impress mates
in the spring breeding season.
After mating in northern
Europe, thrush nightingales
migrate to sub-Saharan Africa
for the winter. In Europe, their
songs are used to defend
territory and attract mates, but
it was unclear why they carried
on singing in the wintering
grounds. “The birds are
practising songs in Africa even
in their later years,” says Abel
Souriau at Charles University
in the Czech Republic.
He and his colleagues
recorded the songs of wild
thrush nightingales in breeding
grounds in Poland and Russia,
and compared them with the
songs heard in wintering
grounds in Tanzania.
They broke down each song
into the syllable-like elements
that make up the melodies,
looking for common patterns.
These include the pairs of notes
that often come at the start
of a song, repeated notes and
complex trills, and the rhythmic
notes typically used at the end.
These elements were in all thesongs recorded in Poland and
Russia. But 89 per cent of the
Tanzanian songs lacked this
structure, were missing the
pauses usually found between
phrases and had high variation
in the notes and trills that make
up the song (Behavioral Ecology
and Sociobiology, doi.org/df8h).
This suggests the birds listen
to their neighbours in the spring
and then remix song elements
into new patterns in a kind of
jam session over the winter.
“What we love in nightingales
is that they sing with so much
complexity and regularity, like
classical music. But this is totally
random vocalisation – there’s no
beginning, no end. It’s more like
improvising,” says Souriau.
Thrush nightingales typically
know between 23 and 42
songs, and they usually learn
them when they are young.
“The winter songs recorded
in this study are more typical
of songs sung during early
song development and suggest
that thrush nightingales
may be singing during the
winter to improve the quality
of their song,” says Marjorie
Sorensen at the University
of Guelph in Canada. ❚AnimalsChelsea WhyteTwisted crystals are
making waves in the
world of chemistryAL
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ANDER^ SHTUK
ENBE
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ISH
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OT
O
Older nightingales
keep up to date
with the latest songs“ I asked everybody in
the world about this.
Nobody knew what the
heck I was talking about”