72 Science & technology The EconomistNovember 28th 2020
21damagewhileadmittinglight.Allthatis
neededafterthisistoattacha sterilisation
chambertooneendofthepipeanda water
supplytotheother,andthenaimthemir-
rorsatthesun.Withanappropriatear-
rangementof valves,thesun’sheat will
boilthe water,heat theresultingsteam
wellaboveboiling-pointandincreasethe
pressureinthetube—andthusalsointhe
sterilisationchamber.
In tests carried out at a hospital in
Mumbai,inpartnershipwiththeIndian
Institute of Technology in that city, Dr
Zhao’snewautoclavewasabletosustain
steamata temperatureof128°Candtwoat-
mospheresofpressure forhalfanhour.
Whentestedwithautoclaveindicatortape,
amaterial used routinely to make sure
autoclavesareworkingproperly,itpassed
withflyingcolours,meaningit wouldhave
successfullysterilisedanythingwithinthe
sterilisationchamber.
Demandforthisproductislikelytobe
high.Some15%ofhospitalpatientsinlow-
andmiddle-incomecountriesgetinfected
whilereceivingtreatment,andsurgeryis
animportantcauseofthisiatrogenesis.Dr
Zhaothereforehopestohavecommercial
versionsreadyby2022.Recognitionforhis
work, as Chamberland might have ob-
served,couldtakea whilelonger. 7I
n the early 1970s American women
gave birth, on average, to 2.12 children
each. By 2018 that figure had fallen to 1.73.
Many alterations in people’s lives have
been invoked to help explain this change,
including the facts that women now are
better educated, more likely to have jobs or
run businesses, and have better access to
contraception than their antecedents of
five decades ago. Also, demand for children
to work as extra pairs of hands on family
farms has dropped.
None of these explanations, though,
overlaps neatly with birth-rate curves. Oth-
er factors must be at work, too. And Jordan
Nickerson and David Solomon, professors
of finance at the Massachusetts Institute of
Technology and Boston College respective-
ly, think they have found an intriguingly
counterintuitive one: America’s increas-
ingly protective child car-seat laws.
Their study, “Car seats as contracep-
tion”, published in ssrn, a repository for
so-called preprint papers that have yet to
undergo formal peer review, examines the
effect that car-seat policies may have had
on American birth rates between 1973 and- During the Reagan era, only the truly
wee—tots aged under three—had normally
to be secured in child-safety seats. But
states’ governments have, since then, grad-
ually ramped up the requirements. Today,
most places in America make children sit
in safety seats until their eighth birthdays.
That concern for youngsters’ safety has had
the unintended consequence, Dr Nicker-
son and Dr Solomon suggest, of fewer
three-child families.
In drawing this conclusion they have
correlated census data with changes in
state laws on safety seats. They discovered
that tightening those laws had no detect-
able effects on the rates of births of first and
second children, but was accompanied by a
drop, on average, of 0.73 percentage points
in the number of women giving birth to a
third while the first two were young
enough to need safety seats. That may not
sound much, but it is a significant fraction
of the 9.36% of women in the sample who
did become third-time mothers.
The authors also made two other perti-
nent observations. The reduction they saw
was confined to households that did actu-
ally have access to a car. And it was larger in
households where a man was living with
the mother. The latter point is relevant,
they think, because this man would take up
NEW YORK
Child-safety laws may have surprising
unintended consequencesChildren’s car seatsBerth control
I
f sharks had bony skeletons, which
preserve easily as fossils, rather than car-
tilaginous ones, which do not, then Otodus
megalodonwould probably be as famous as
Tyrannosaurus rex. Even though only its
teeth are routinely available for study, it
has starred in at least one film, “The Meg”,
released in 2018. Were it better known, a
whole ocean-based franchise akin to “Ju-
rassic Park” might now exist.
No matter. It is still an intriguing ani-
mal. Adults are reckoned to have reached a
length of 18 metres. (T. r e xwas 12 metres
from snout to tip of tail.) And megalodons,
as they are called colloquially, lasted as a
species from the beginning of the Miocene
epoch 23m years ago to 3m years ago, dur-
ing the Pliocene. That is far longer than T.
rex’s brief appearance 68m-66m years ago
at the end of the Cretaceous. Their family
life has, however, hitherto been obscure.
Perhaps “family” is a slight exaggera-
tion. But many modern sharks lay their
eggs (or, if viviparous, give birth) in places
known as shark nurseries. Jose Herraiz ofthe University of Valencia and his col-
leagues wondered if that had also been true
of megalodons. As they report this week in
Biology Letters, it seems it was.
Shark nurseries are shallow coastal ar-
eas that have abundant food available and
are, precisely because of their shallowness,
difficult for predators like other, bigger
sharks to move around in. Some 16m years
ago part of north-eastern Spain, between
what are now the cities of Barcelona and
Tarragona, was just such a shallow, protect-
ed bay. And two quarries dug into the rock
that formed from the sediment in this bay
have yielded a number of megalodon teeth.
Shark’s teeth indicate, by their size and
shape, the size of their possessor’s body.
That is how O. megalodon’s adult length has
been estimated. But body size within a spe-
cies is also a good indicator of age. Dr Her-
raiz and his colleagues therefore studied
the 25 best-preserved megalodon teeth
from these quarries, to deduce the size dis-
tribution, and thus the age distribution, of
the sharks that had lived there.
To do so they used a formula for length
determination worked out for great whites,
the largest existing shark that hunts indi-
vidual prey. (There are larger species, such
as the whale shark and the basking shark,
but these filter small prey from the water in
a manner similar to baleen whales.) Apply-
ing this formula to the teeth from the quar-
ries, they found that the sharks in question
had probably ranged in length from about
three to 14 metres. These animals were
therefore either juveniles or small adults,
suggesting it was, indeed, a nursery.
Thus encouraged, the researchers then
applied their method to eight other sites
from which megalodon teeth have been re-
covered (see chart). Four were similarly
youngster-dominated. The other four were
dominated by adults. They therefore think
they have identified five megalodon nurs-
eries. The remainder, they suspect, were ei-
ther breeding grounds or feeding grounds
for grown-ups. 7How one of history’s most formidable
marine predators raised its youngPalaeontologyNursery days
The shark has pretty teeth, dearSource:“Useofnursery areas by the extinct megatooth shark
Otodus megalodon”, J. L. Herraiz et al., 2020, Biology LettersEstimatedlengthsofO.megalodonsharks,metresSite
Bone valley
Calvert
Gatun
Chucunaque
Tarragona
Yorktown
Temblor
Pisco
Bahia Inglesa0 5 10 15 20Neonate Juvenile AdultDistribution
of fossils