Before the germ theory of disease,
urban dwellers placed great stock in
odors—foul and fresh—as indicators
of environmental health. This week on
the Science podcast, historian Melanie
Kiechle describes the rise and fall of
the sense of smell in the 19th-century
fight for fresh air.
In the 1800s, foul odors were believed to cause disease, leading
many city residents to use their noses to make sense of sanitation.
In their seminal book Evolution and Healing, Randolph Nesse and George C. Williams describe the design of human bodies as “simultaneouslyextraordinarily precise and unbelievably slipshod.” In- deed, they conclude that our inconsis-
tencies are so incongruous that one could be
forgiven for thinking that we had
been “shaped by a prankster.”
By what agency did this unfor-
tunate state of affairs come into
being, and how might we amend
it? Gene editing and synthetic
biology offer the possibility of, re-
spectively, “correcting” or “rewrit-
ing” human nature, allowing us
to expunge unfavorable aspects of
ourselves—such as our suscepti-
bility to diseases and aging—while
enabling the introduction of more
appealing features. The legitimacy
of such enterprises, however, to
some extent depends on whether the evolu-
tion of humans on Earth was inevitable.
If our origin and nature were deterministi-cally programmed into life’s history, it would
be hard to argue that we should be any other
way. If, on the other hand, we are the improbable products of a historically contingent
evolutionary process, then human exception-alism is compromised, and the artificial modification of our genomes may be perceived by
some as being less of an affront to the natural
order. In his compelling book Improbable
Destinies, Jonathan Losos addresses this issue, recasting previous dialogues in the light
of an experimental evolutionary agenda and,
in so doing, arrives at a novel conclusion.
Until recently, the evolutionary determinism debate focused on two contrary interpretations of an outcrop of rock located in a
small quarry in the Canadian Rocky Mountains known as the Burgess Shale. Contained
within the Burgess Shale, and uniquely preserved by as-yet-unknown processes, are the
fossilized remains of a bestiary of animals,
both skeletal and soft-bodied. These fossils
are remarkable in that they appear to have
originated in a geological instant 570 to 530
million years ago during the Cambrian. They
An Olfactory History of
Nineteenth-Century Urban America
Melanie A. Kiechle
University of Washington Press,
2017. 387 pp.
A biologist sheds light on the evolutionary
likelihood of human existence
The reviewer is the author of Life Without Genes (Flamingo,
London, 2000). Email: email@example.com
Inevitable or improbable?
INSIGHTS | BOOKS
tion, contemporary evolutionary biologists
have realized that evolution can occur in
rapid bursts and may consequently be captured on the wing.
Given that microbes have an intergenerational time of 20 minutes or less, in 1988,
the evolutionary biologist Richard Lenski
reasoned that the bacterium Escherichia coli
would comprise the perfect model experimental system to study condensed evolutionary time scales. Bacteria could additionally
be frozen, allowing multiple parallel replays
to be run again and again from any time
point in their history. Twenty-eight years and
64,000 bacterial generations later, he concluded that the history of life owes its complexity both to repeatability and contingency.
Losos and other investigators have demonstrated a similar degree of repeatability in the
natural evolution of the Anolis lizard, three-spined sticklebacks, guppies, and deer mice.
Importantly, however, when experimental
populations evolve in divergent environments, novel outcomes are more commonly
observed than convergence.
These experiments were not a replay of
the tape of life in time so much as a replay
in space, but the findings were surprising in
that they emerged within a relatively short
time frame—a far cry from what one might
have expected would be necessary to falsify
the predictability hypothesis.
Losos concludes that “both sets of forces—
the random and the predictable … together
give rise to what we call history.” With this,
humans are humbled once again, cast firmly
into the sea of ordered indeterminism. Although he does not attempt to use this as a
justification for human genomic modification, Losos argues that the genetic principles
underlying life’s multifarious convergent
solutions might, among other things, be co-opted to rescue imperiled species. j
By Adrian Woolfson comprise a bizarre zoo of outlandish body
plans, some of which appeared to be unrepresented in living species.
In his 1989 book Wonderful Life, the Harvard biologist Stephen Jay Gould argued
that the apparently arbitrary deletion of distinct body plans in the Cambrian suggests
that life’s history was deeply contingent,
underwritten by multiple chance events. As
such, if the tape of life could be
rewound back to the beginning
and replayed again, it would be
vanishingly unlikely that anything
like humans would emerge again.
The Cambridge paleontologist Simon Conway Morris, on the other
hand, would have none of this.
Citing a long list of examples
to illustrate the ubiquity of convergence—the phenomenon
whereby unrelated species evolve
a similar structure—Conway Morris claimed that the evolution
of humanlike organisms would
be a near inevitability of any replay. In his
scheme, articulated in 2003 in Life’s Solution, nature’s deep self-organizing forces
narrowly constrain potential evolutionary
outcomes, resulting in a relatively sparse
sampling of genetic space.
Losos closes the loop on this contentious
debate, marshaling data from the burgeoning research area of experimental evolution.
Unlike Darwin, who perceived the process
of evolution to be imperceptibly slow and
therefore inaccessible to direct experimenta-
Fate, Chance, and
the Future of Evolution
Jonathan B. Losos
Riverhead Books, 2017.