Scientific American 2021 05.pdf
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MAY 2021
SCIENTIFICAMERICAN.COM
A New Map
of the Universe
Alzheimer’s and the
Blood-Brain Barrier
How to Help
Adolescents
Flourish
JOURNEY
INTO THE
AMERICAS
Genetic and archaeological
discoveries tell a new story about
how the continents were populated
M ay 2 0 2 1
VO L U M E 3 2 4 , N U M B E R 5
00
48
A N T H R O P O LO G Y
C O N S E R VAT I O N
26 Journey into
the Americas
The peopling of the American
continents was vastly more
complex than previously thought,
involving multiple populations
over tens of thousands of years.
By Jennifer Raff
A STROPHYSIC S
48 Coral Cocktails
Can doses of probiotics save
coral reefs from extinction?
By Elizabeth Svoboda
MIND
56 Age of Opportunity
A refined understanding of the
adolescent brain could lead to
improvements in education and
mental health.
By Lydia Denworth
ANIMAL COGNITION
34 A New Map
of the Universe
A chart of millions of galaxies
across 11 billion years of cosmic
history helps to answer some of
the biggest cosmological questions.
By Kyle Dawson and Will Percival
NEUROSCIENCE
62 The Riddle
of Dolphin Handedness
Studying lateralization in
cetaceans identified a quirk
of human perception.
By Kelly Jaakkola
M AT H E M AT I C S
MICHAEL BERUMEN AND MORGAN BENNETT-SMITH
42 Holes in the Shield
Leaks in the protective blood-brain
barrier may lead to Alzheimer’s and
other dementias. Reversing the
damage makes aging animal brains
look young and healthy.
By Daniela
Kaufer and Alon Friedman
ON THE C OVE R
The peopling of the Americas was once thought
to be a simple process: a group of hunters
migrated from East Asia in pursuit of game
animals around 13,000 years ago and gave
rise to the Indigenous peoples who live on
these continents today. Recent genetic and
archaeological finds have upended this tidy story.
Illustration by Winona Nelson.
66 Chalkboard Art
A photography project reveals
the allure of topology, geometry
and mathematical theory.
By Clara Moskowitz
May 2021, ScientificAmerican.com
1
4 From the Editor
6 Letters
8 Science Agenda
The people who investigate premature deaths
should have medical training.
By the Editors
10 Forum
Rename the James Webb Space Telescope.
By Chanda Prescod-Weinstein, Sarah Tuttle,
Lucianne Walkowicz and Brian Nord
10
12 Advances
Plumbing the depths of Saturn’s moon Titan. A crime-
scene test for human or animal blood. An exceptionally
explosive mud volcano. The rapid evolution of cichlid fish.
22 Meter
The vibrancy of string theory revealed.
By Richard A. Jones
24 The Science of Health
COVID has inspired faster and better clinical trials.
By Claudia Wallis
76 Recommended
12
Chemistry as a visual art. Continuing inscrutability
of quantum mechanics. The enduring misogyny of
medicine. Grappling with our information ecosystem.
By Andrea Gawrylewski
77 Observatory
What counts as a “hard” problem? It’s not as intuitively
obvious as we might think.
By Naomi Oreskes
78 50, 100 & 150 Years Ago
By Mark Fischetti
80 Graphic Science
76
Every season has its hormonal highs and lows.
By Mark Fischetti and Accurat
Scientific American (ISSN 0036-8733), Volume 324, Number 5, May 2021, published monthly by Scientific American, a division of Springer Nature America, Inc., 1 New York Plaza, Suite 4600, New York, N.Y. 10004-1562. Periodicals
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Printed in U.S.A. Copyright © 2021 by Scientific American, a division of Springer Nature America, Inc. All rights reserved.
Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at www.springernature.com/us). Scientific American maintains a strict
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2
Scientific American, May 2021
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