The Economist - USA (2021-07-10)

The Economist July 10th 2021 Science & technology 73

rous  natural  resources that we exploit
come ultimately from ancientvolcanoes.”
In  particular,  in  2015,heandhiscol­
leagues worked out the chemicaldetailsof
how copper­sulphide oresformwhensul­
phur­rich gases rise throughtheplumbing
of  active  volcanoes  and  encountermetal­
rich  brines  trapped  in  rockssittingjust
above  pockets  of  magma.Modernmining
operations  dig  up  examplesoftheseores
that  formed  millions  orbillionsofyears
ago. Dr Blundy proposes insteadtocutout
the middleman and go straighttothedeep
copper­rich fluids themselves.
As  he  writes  in  OpenScience, hesus­
pects these are found beneatheveryactive
and dormant volcano, thoughtheconcen­
tration  of  copper  in  thebrineconcerned
will vary from place to place.Hisevidence
comes  from  electromagneticsurveyscar­
ried  out  on  some  40  volcanoes,including
Mount  Fuji  in  Japan,  MountStHelensin
America  and  others  in  Bolivia,NewZea­
land, the Philippines andelsewhere.These
surveys  consistently  pickuphighlycon­
ductive  zones  2km  or  morebeneaththe
surface,  for  which  the  simplestexplana­
tion  is  the  presence  of  super­saltymetal­
rich  brines.  This  conjectureisreinforced
by analysis of rock samplesrecoveredfrom
such depths under a numberofvolcanoes.
These do indeed containbrineswithvary­
ing  concentrations  of  copper,aswellas
other  valuable  metals  includinglithium,
zinc, gold and silver. 
All  this  suggests  thatcoppercouldbe
drilled  for  commerciallyinthesameway
that  oil  is—except  that  theboreholesin­
volved would be considerablydeeper.That
would be difficult, but notoutoftheques­
tion.  It  would  require equipment that
could withstand temperaturesgreaterthan
400°C  and  contact  withbrinestentimes
saltier  than  seawater.  Buttheprizewould
be worth it.
Individual volcanoes would,admitted­
ly,  yield  only  a  fraction  oftheoutputofa
big  copper  mine.  Dr  Blundyandhiscol­
leagues  estimate,  for  example,thatthere
might be as much as 1.4mtonnesofcopper
beneath New Zealand’s WhiteIslandvolca­
no  (pictured  on  previouspage),whereas
the world’s largest minesholdtensofmil­
lions  of  tonnes  of  it.  Butthereareonlya
handful of such mines, mostinmountain
ranges near the Pacific coastoftheAmeri­
cas. By contrast, hundredsofvolcanoesex­
ist around the world, readybetapped.
The  temperature  at  whichtheequip­
ment  used  would  have  tooperate,more­
over,  brings  an  opportunity.Theheatin­
volved  might  be  employed to generate
electricity—enough  to  powerthedrilling
operation and perhaps eventoyielda sur­
plus.  Sucking  copper  outofEarth’scrust
through  2km­long  strawsmightthus be
that  rare  thing  in  the  miningindustry,an
actual environmental good.n

Theoriginofsongbirds

The sweet taste

of success

I

maginea worldwithoutbirdsong.Yet

thismighthavecomeaboutifithadnot

beenfora geneticchangethathappened

some30myearsago,atthebeginningof

theevolutionofthePasseri,togivesong­

birdstheirpropername.

Birdsevolvedfromcarnivorousdino­

saurscalledtheropods.Meateatersneed

notdetectsugarinthewaythat,say,fruit

eatersdo,andgeneticanalysesofmodern

birdssuggesttheirtheropodancestorhad

losttheabilitytotastesweetness.Today,

however,manybirdshavesugar­richdiets

ofnectarorfruit,soperceivingthingsas

sweetisausefulattribute.Andresearch

justpublishedinSciencebyTodaYasukaof

TokyoUniversity andMaudeBaldwinof

theMaxPlanckInstituteforOrnithologyin

Seewiesen, Germany,suggestssongbirds

can indeedperceive sweetness. Thisre­

evolvedabilitymayhavebeeninstrumen­

talintheirsuccess.Sincealmosthalfthe

birdspeciesnowalivearePasseri,thatis

nosmallmatter.

Vertebrates’taste­receptor genesnor­

mallyincludethreethatencodeproteins

calledt1r1,t1r2andt1r3. Thetasterecep­

torsthemselvesareformedfrompairsof

theseproteins.Receptorsforsweetnessare

a combination of t1r2 and t1r3. Birds,

however,lackthegenefort1r2. Presum­

ably,itwaslostbytheirtheropodances­

tors,whichdidnotneedit.DrToda’sand

DrBaldwin’sexperimentshaveshownhow

thislosswasreversed.

Thepair’sfirststudy,publishedin2014,

wasonhummingbirds,whichfeedonnec­

tar  from  flowers.  It  found  that  humming­

birds regained the ability to taste sugars via

mutations  in  the  genes  for  t1r1and  t1r3.

The  receptor  formed  by  combining  t1r1

and t1r3normally detects umami, a savou­

ry  flavour  typical  of  meat.  In  humming­

birds, these mutations allow this receptor

to detect sugars, too. Dr Toda and Dr Bald­

win therefore wondered whether that was

also the case for songbirds.

To find out, they cloned t1r1­t1r3recep­

tors from a variety of songbirds and tested

their  responses  to  sugar.  All  the  receptors

they  tested—from  birds  with  sugar­rich

and  sugar­poor  diets  alike—interacted

strongly  with  sugar  molecules.  This  con­

firmed that, as with hummingbirds, song­

birds regained perception of sweetness via

mutations of the gene for t1r1and t1r3. By

contrast, umami receptors cloned from the

Tyranni,  a  sister  group  to  the  Passeri,  did

not  interact  with  sugars,  though  they  did

so  strongly  with  amino  acids  typical  of

meat.  The  mutations  in  the  songbird  li­

neage  must  thus  have  happened  after  the

Passeri and Tyranni lines diverged, but be­

fore the Passeri themselves began prolifer­

ating into their current variety.

Intriguingly, when Dr Toda and Dr Bald­

win looked at the molecular modifications

which  allowed  the  t1r1­t1r3receptors  of

hummingbirds  and  Passeri  to  detect

sweetness,  they  found  them  to  be  com­

pletely  different.  Both,  though,  involved

numerous changes to the underlying dna,

suggesting a strong evolutionary pressure

to optimise them. This pressure was prob­

ably  a  consequence  of  competition  to  fill

the new ecological niches opened up by an

ability  to  recognise  sweet  things  as  both

edible  and  nutritious.  And  it  was  that

which resulted in the Passeri’s current di­

versity. How all this ties up with the melli­

fluous songs sung by many members of the

group  is  unclear.  It  mayjustbe  a  coinci­

dence.  But  if  so,  for  thosewhoenjoy  bird

song, it is a fortunate one.n

Songbirds can detect sugar. That may

explain their ubiquity

Something to sing about