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72 Science and technology The Economist September 22nd 2018
1
2 fects on children. For instance, work in ani-
mals suggests that exposure to nicotine
could be bad for adolescent brains, making
users more susceptible to other addictive
substances later in life. This could be one
reason why human smokers who start
young have higher rates of addiction as
adults. It might also mean that children
who vape risk a lifelong addiction to nico-
tine, andmay even start smoking. But, says
Dr West, these concerns have not yet been
borne out by epidemiological studies.
Smoking during adolescence has also
been associatedwith lasting cognitive and
behavioural impairments, including on
working memory and attention. Animal
tests suggest that exposure to nicotine spe-
cifically could explain at least some of that
effect. All this forms the scientific backdrop
to the FDA’s worries about the effects of
vaping among the young.
Getting definitive answers will take
time. Epidemiology is a tricky business. All
sorts of confounding factors and over-
looked connections can skew conclusions.
Smoking stands out inmedical history as a
pastime which is so unambiguously bad
for you that the signal cuts through almost
anyamount ofnoise. The truth about e-cig-
aretteswill take longer to tease out.
That may sound frustratingly vague.
But it points to at least one clear conclu-
sion—whether it is harmless or only mod-
erately bad for you, vaping is almost cer-
tainly safer than smoking. That is a
message which needs spreading. In Britain
about a third of smokers say they have not
tried vaping because they are worried
about its safety and addictiveness. This at-
tachment to a known evil is self-defeating.
At least for now, the e-cigarette looks like a
useful innovation in public health. 7
THE deep sea is full of fantastical crea-
tures. Gelatinous pink sea pigs shovel
food with arms like tiny sea anemones.
Delicate tripod fish stand on chopstick-like
stilts. Barreleye fish have transparent
heads that reveal all their internal work-
ings. Giant larvaceans hold a well-de-
served spot on this list of curiosities.
Shaped like oversized sperm, with a head
andwide tail, the faintly blue tunicates are
just ten centimetres long. But their
“houses”, ephemeral structures which the
creatures build froma film-like mucus, can
be up to ametre across.
Larvaceans are a familiar sight to deep-
ocean biologists. But, as Bruce Robison at
the Monterey Bay Aquarium Research In-
stitute (MBARI) told a conference in Cali-
fornia earlier this month, it is only in the
past few years that scientists have been
able to study the animals in their native en-
vironment. Doing so has helped to answer
the question of just why there is so much
life on the floor of the deep ocean, where
foodwas thought to be scarce.
A larvacean’s house comes in two
parts. The inner house is made up of two
symmetrical lobes and looks a bit like a
translucent brain that hovers just above
the animal. Around those lobes is a larger
and less well-defined external house. Both
act as filters, channelling nutrient-rich wa-
ter towards the larvacean inside. Once
they become clogged, roughly every 24
hours, the larvaceanwhisks itself out with
a flickof its tail and builds a fresh dwelling.
The abandoned houses collapse in upon
themselves and sink to the sea floor.
As they sink, these discarded dwellings
take with them all the particles trapped in
their filtration systems, much of which is
dead organic matter. By shadowing the
sinking structures with remotely operated
submersibles called ROVs, Dr Robison
measured their rate of descent at around
800 metres per day. By contrast smaller,
free-floating organic particles, known as
“marine snow”, sink at a rate of just centi-
metres a day. Marine snow is the main
food source for deep-ocean ecosystems.
But because it sinks comparatively slowly,
microbes in the water are able to digest
much of the food along the way, consum-
ing it before it reaches the oceanfloor. Since
the sinkers move much faster, microbes
have less time to nibble away at their cargo
before they reach the bottom.
That finding has helped solve a long-
standing mystery in marine biology. Ken
Smith, one of Dr Robison’s colleagues,
studies the ecosystems at the bottom of
Monterey Bay, more than 4,000metres be-
low the surface. The organisms living there
seemed tobe expending significantlymore
energy than the marine snowwas provid-
ing. The difference, Dr Robison believes,
can be accounted for by discarded larva-
cean houses. He reckons they could ac-
count for a third of the energy available on
the ocean floor. Andwhat is true ofMonte-
rey Bay is probably true elsewhere, too.
Larvaceans have beenobserved all around
the Pacific and Atlantic oceans.
Larvacean houses may also help to ex-
plain why microscopic particles of plastic
have been discovered in the ocean’s deep-
est depths. Plastic fragments should float,
but if they become trapped inside the snot-
like globs of discarded larvacean houses,
they can be dragged down into the abyss.
Kakani Katija, another of Dr Robison’s
colleagues, has designed a laser scanner
for the aquarium’s ROV. She has injected
microplastics into the water around giant
larvaceans and watched as they were
sucked into the filters. The plastic endedup
in the animal’s faeces and houses, both of
which ferried them into the deep. At the
conference this month, she described col-
lecting sinkers from the deep ocean that
were full of microplastics. What effect
those plastics are having on the rest of the
deep-seaworld is, for now, unknown. 7
Marine biology
The house that
sank
Creatures called giant larvaceans help
ferry food—and pollution—to the deeps
Snot houses of the abyss
ONE tale of Nasreddin, a self-satirising
13th-century philosopher, tells of the
time he lost a precious ring. When his wife
asks why he is searching in the yard rather
than inside, where the ring was lost, Nas-
reddin explains that the light is better out-
side. Looking for something where the
search is easiest is a form of bias now
known as the “street light” effect. A study
published this week in PLOS Biology re-
ports a similar skew in modern genetics
that may be leaving thousands of impor-
tant genes largely unstudied.
There are roughly 20,000 genes in the
human genome. Understanding genes and
the proteins theyencode canhelp tounrav-
el the causes of diseases, and inspire new
drugs to treat them. But most research fo-
cuses on only about ten percent of genes.
Thomas Stoeger, Luis Amaral and their col-
leagues at Northwestern University in Illi-
nois used machine learning to investigate
why that might be.
First the team assembled a database of
430 biochemical features of both the genes
themselves (such as the levels at which
Genetics
Whoever has will
be given more
Scientists and funding agencies hewto
familiar genes