Science - USA (2021-11-12)

828 12 NOVEMBER 2021 • VOL 374 ISSUE 6569 science.org SCIENCE

ILLUSTRATION: MARK WITTON

W

ith dramatic flair, Henry Gee’s

sweeping new book, A (Very) Short

History of Life on Earth, tells the

4-billion-year story of life on this

planet and how it has been re-

peatedly shaped by geological, cli-

matic, and atmospheric forces. Trained as a

paleontologist, Gee tells life’s history using

the framework of the fossil record, offering

insights from the related fields of ecology

and physiology. Interwoven as it is with geol-

ogy and climate, life evolves the way Ernest

Hemingway said we go broke: “gradually and

then suddenly” ( 1 ).

Life emerged on Earth not long after the

planet’s aggregation, writes Gee, and faced its

first major challenge about 2.4 billion years

ago. Until this point, bacteria and archaea

had been confined to the oceans, where they

evaded the Sun’s deadly rays, which were not

yet tempered by a protective atmosphere.

Bacteria eventually learned to harness sun-

light to produce energy, with oxygen as a

by-product; but as oxygen levels rose, gen-

erations of bacteria and archaea that had

evolved in its absence were burned alive.

Later, continental collisions and volcanic

eruptions caused waves of extinctions that

wiped ancient species from the face of the

EVOLUTIONARY BIOLOGY

By Itai Yanai^1 and Martin J. Lercher^2

Iterations of evolution

Earth and propelled previously insignifi-

cant lineages into suddenly emptied ecolog-

ical niches. The book returns often to this

theme, reminding readers how creatures

that dominated certain periods of Earth’s

history—the dinosaurs of the Jurassic, for

example, or the mammals of the Cenozoic—

spent millions of years as minor players

before taking center stage. Life, it seems,

cannot help but exploit each new crisis it

encounters as an opportunity for diversifi-

cation. In this way, it is akin to the

mythical phoenix, which is regu-

larly consumed in a fiery inferno,

only to rise again from the ashes.

The main protagonists of Gee’s

book are vertebrate life-forms.

Early vertebrates, which began

as fish, evolved jaws, the better to

shred other organisms with. Even

after they began moving onto land,

they still returned to the water to

reproduce. Vertebrate embryos,

notes Gee, need a liquid medium

in which to develop. Thus, the most crucial

vertebrate adaptation may have been the egg,

which provides a liquid capsule in which life

can unfold on dry land.

Another amazing early vertebrate adapta-

tion was the development of air sacs, which

first arose in dinosaurs and are still found in

birds. This adaptation, which enabled a one-

way system of air flow, also doubled as an ef-

ficient cooling system for internal organs.

As forests became more and more frag-

mented owing to climate changes linked to

continental drift, primates started to venture

into the open grasslands, from where the

earliest hominins arose 7 million years ago.

Their bipedal stance, notes Gee, made them

“almost preternaturally maneuverable.”

About 2.5 million years ago, Homo erectus

arose, a territorial savannah predator, deadly

thanks to two traits: it was a powerful long-

distance runner and a social animal. From

this lineage, Homo sapiens evolved. Human-

ity’s first attempt at worldwide dispersal

failed, shattered by the cold of an ice age

200,000 years ago. Confined to an oasis in

what is now the Kalahari Desert, humankind

nearly went extinct. We, as a species, are just

as fragile as all the others, reminds Gee.

With beautiful exposition, Gee describes

the major anatomical, physiological, and

behavioral transitions in life’s evolution. He

largely refrains, however, from discussing

the mechanisms and agents of evolution,

and he does not offer much evidence from

fields other than geology and paleontology.

With few references to genes and genomes,

the book lacks an appreciation of the mecha-

nisms by which the genes—the ultimate rep-

licators ( 2 , 3 )—both constrain morphological

change and enable incredible diversifications.

Gee’s unbridled excitement also prompts

him to sacrifice some precision and downplay

some scientific uncertainties in the interest

of storytelling. He frequently puts forward

matter-of-fact description of topics that are

far from settled and weaves in his own “fan-

ciful speculations,” freely admitting to these

liberties in the endnotes. He advances a con-

jectural internal anatomy of Sacco-

rhytus, a progenitor of vertebrates,

for example; speculates about the

reproductive strategies of ancient

amphibians; and articulates how

Stone Age shamans might have

performed coming-of-age rituals.

Some hundreds of million years

from now, Earth will become un-

inhabitable to even the hardi-

est organ isms, spelling the final

doom for Earth-evolved life—

unless, perhaps, some earthlings

manage to escape into space first. Mean-

while, the reader is rewarded with a deeper

appreciation of our own place in the grand

scheme of life, where even the best-adapted

species disappear within a time that is min-

ute on the scale of evolution. j

REFERENCES AND NOTES

1. E. Hemingway, The Sun Also Rises (Scribner’s, 1926).


2. R. Dawkins, The Selfish Gene (Oxford Univ. Press, 1976).


3. I. Yanai, M. Lercher, The Society of Genes (Harvard Univ.
   Press, 2016).
   10.1126/science.abm0121

Mammals forage on the banks of a lagoon 145 million

years ago in this artist’s rendering.

A paleontologist’s history of life highlights the recurring role

played by geological, climatic, and atmospheric forces

BOOKS et al.

The reviewers are at the^1 Institute for Computational

Medicine, NYU Langone Health, New York, NY 10016, USA,

and^2 Department of Biology and Institute for Computer

Science, Heinrich Heine University, 40225 Düsseldorf,

Germany. Email: [email protected]

A (Very) Short History

of Life on Earth

Henry Gee

St. Martin’s Press,

2021. 288 pp.