16 | New Scientist | 9 November 2019ZoologyBrainwaves help
take out the trashAS YOU sleep, slow waves of
electrical activity in your brain
seem to help rinse away waste
products that could harm cells.
This may play a role in preventing
conditions such as Alzheimer’s.
Brainwaves are made by large
networks of brain cells firing
together in rhythm, but much
about their function is unclear.
To see if they play a role in cleaning
the brain, Laura Lewis at BostonÖtzi’s attempt to flee
his pursuers chartedMOSS buried alongside Ötzi the
Iceman bolsters the theory that
his last journey was through a
gorge, possibly fleeing someone.
The well-preserved 5300-year-
old mummified body was found
in the Alps on the border of Italy
and Austria in 1991. His demise
was gruesome: he probably bled to
death after being hit by an arrow.
Now James Dickson at the
University of Glasgow, UK, and his
colleagues have used thousands of
fragments of moss and liverwort
buried alongside or inside Ötzi to
understand his final days.
The plants were from at least 75
different species, only 23 of which
live in that precise area today. One
of the most intriguing discoveries
was of the bog moss Sphagnum
affine in Ötzi’s colon. This moss
is typically found in wetlands and
probably came from the bottom
of the Vinschgau valley in SouthAncient humans NeuroscienceFEMALE Asian elephants stop
reproducing towards the end of
their lives, putting them among
the few species that experience
something akin to the menopause.
Only humans, orcas, narwhals,
beluga whales and short-finned
pilot whales are known to exhibit
what biologists call extended
post-reproductive lifespan.
The existence of such a stage
is an evolutionary riddle: why
should individuals give up trying
to leave more descendants?
Now Asian elephants have been
added to the list, thanks to Simon
Chapman at the University of Turku,
Finland, and his team. They studied
records of 3802 female elephants
used in timber camps in Myanmar
between 1940 and 2018. Their
mortality and fertility patterns are
like those of wild Asian elephants.The oldest in this group lived into
their 70s, but most had their last
calf by 55. The team calculates that
the proportion of years lived by
females in a post-reproductive
phase is 16 per cent: some way
short of humans’ 43 per cent but
considerably more than African
elephants’ 4 per cent (BMC
Evolutionary Biology, doi.org/ddhj).
In elephants, halting reproduction
may be behavioural rather than
physiological, says Chapman. Such
behaviour could be a step towards
evolving a true menopause.
One idea to explain menopause is
the grandmother hypothesis. It says
that if older females help care for
grandchildren, they end up with
more descendants than by having
more children of their own. There is
some evidence for this in the Asian
elephants studied. Sam WongElephants found to have
menopause-like stage of life
University, Massachusetts,
and her team used EEG caps to
measure electrical activity in the
brains of 13 people while they
napped inside MRI scanners.
They also monitored blood
oxygen levels (in red, pictured)
in their brains and the flow
of cerebrospinal fluid, a watery
liquid that surrounds the brain
and spinal cord. The team found
that, during sleep, large waves of
cerebrospinal fluid flow into and
out of the brain every 20 seconds,
a process thought to remove
waste. The inward flow was
preceded by patterns of slow
waves of electrical activity.
These brainwaves coincided
with blood flowing out of the
brain, which the team says helps
balance the total volume of fluid
around the brain (Science,
doi.org/ddmr).
People with Alzheimer’s have
fewer slow brainwaves, says Lewis.
However, it isn’t clear whether this
is a cause or a symptom of the
condition. Layal LiverpoolTyrol, Italy. Some people believe
this was Ötzi’s home as an adult.
The moss had long been used
for staunching wounds because
of its mild antiseptic properties.
It may have been used to treat a
deep wound he received to his
right palm possibly 48 hours or
less before his death, says Dickson.
Dickson was also surprised
to find fragments of the moss
Neckera complanata in his
intestines, a low-altitude moss
of the woodlands. Ötzi was found
at 3200 metres above sea level,
which is way above the treeline.
This suggests Ötzi travelled
from the forests below, possibly at
1200 metres but maybe as low as
600 metres above sea level, and
went north up a gorge (PLoS ONE,
doi.org/ddhp).
“It seems puzzling that he took
the most stressful track through a
gorge, but considering scenarios
that he was on the run, a gorge
provided most opportunities to
hide,” Dickson and his colleagues
write. Ruby Prosser ScullyTONY HEALD/NATURE PL
FULTZ ET AL. 2019News In brief