Life Concepts from Aristotle to Darwin: On Vegetable Souls

268 Pages·2018·3.45 MB·English

by  Lucas John Mix

Luca s John M ix
L I F E
C O N C E P T S
F R O M
A R I S T O T L E
T O
D A R W I N
On Vegetable Souls
Life Concepts from Aristotle to Darwin
Lucas John Mix
Life Concepts from
Aristotle to Darwin
On Vegetable Souls
Lucas John Mix
Department of Organismic and
Evolutionary Biology
Harvard University
Cambridge, MA, USA
ISBN 978-3-319-96046-3 ISBN 978-3-319-96047-0 (eBook)
https://doi.org/10.1007/978-3-319-96047-0
Library of Congress Control Number: 2018948656
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P
reface
When I first encountered the vegetable soul, I thought it an odd curios-
ity, a strange turn of phrase. As I investigated, I began to realize it had an
important part to play in the history of “life” as we know it. Vegetable
souls oriented biology for two millennia through the influence of Plato,
Aristotle, Lucretius, Pliny, Origen, Plotinus, Ibn Sînâ, Maimonides, and
Aquinas. They influenced the shift to modern biology through Gassendi,
Leibniz, and Hegel. And yet, I could find no systematic account, no
story of vegetable souls. The very term seemed laden with contradiction
and was unknown to many historians and philosophers.
I set out to write the book I wanted to read: a history of theories of
life prior to Darwin, in particular a history of vegetable souls.
As we move forward in biology, exploring the origins of life on Earth,
the possibility of life elsewhere, and the very boundaries of individuality
(genetic, microbial, and neurological), it seems worthwhile to review where
we have been. Some of the connections we wish to make, between physics
and biology, biology and humanity, have been proposed before. Past suc-
cesses (and failures) can help us evaluate which concepts work for us.
Such a project would not have been possible without generous sup-
port from multiple sources. David Haig, John Wakeley, and the Harvard
Department of Organismic and Evolutionary Biology graciously hosted
me and granted me access to the amazing Ernst Mayr Library. Parts of
this project were made possible through the support of a grant from the
John Templeton Foundation. (The opinions expressed in this publication
are those of the author and do not necessarily reflect the views of the
v
vi PrEFACE
John Templeton Foundation.) I was also greatly aided by a year at the
Center of Theological Inquiry, where I was a resident for the 2015–2016
inquiry into the “Societal Implications of Astrobiology.” During that
year, I was able to discuss life-concepts in depth with theologians and
philosophers. The number of people who inspired, informed, and cor-
rected me is too great to name.
I owe specific thanks to Andrew Accornero, Andrew Berry, Bill
Brown, Luis Campos, David Haig, and Matt Quarterman for reading
chapters and providing comments. Thanks are due as well to my family
and colleagues who put up with five years of postponing other projects
to pursue this topic. I am deeply grateful.
Cambridge, USA Lucas John Mix
c
ontents
1 Vegetable Souls? 1
Part I Birth
2 Greek Life: Psyche and Early Life-Concepts 17
3 Strangely Moved: Appetitive Souls in Plato 29
4 Three Causes in One: Biological Explanation in Aristotle 43
5 Life in Action: Nutritive Souls in Aristotle 55
6 Plants Versus Animals in Hellenistic Thought 67
Part II Development
7 The Breath of Life: Nephesh in Hebrew Scriptures 79
8 Life After Life: Spiritual Life in Christianity 91
9 Invisible Seeds: Life-Concepts in Augustine 103
vii
viii CONTENTS
10 Aristotle Returns: A Second Medieval Synthesis 117
11 Life Divided: Vegetable Life in Aquinas 129
Part III Death
12 Mechanism Displaces the Soul 143
13 Divided Hopes: Physics Versus Metaphysics 159
14 Ghosts in the Machine: Vitalism 175
15 The Same and Different: Early Theories of Evolution 189
16 Vegetable Significance: Evolution by Natural Selection 199
Part IV New Life
17 “Vegetables” Versus Modern Plants 213
18 Vegetable Individuality: The Organismal Self 225
19 Animal Individuality: The Subjective Self 239
20 What Can Be Revived (and What Cannot) 249
Author Index 259
Subject Index 265
CHAPTEr 1
Vegetable Souls?
The term “vegetable soul” troubles the ear. The two words have such
different contexts that joining them strikes us as either funny or non-
sensical. It conjures images of tortured carrots and zombie broccoli.
Surprisingly, vegetable souls were one of the most popular ways of
describing life prior to the renaissance. The Aristotelian idea of souls
as the efficient, formal, and final cause of life dominated discussions of
plant life in Europe and adjacent regions from classical antiquity through
the High Middle Ages, roughly 2000 years. And yet the idea has disap-
peared from our vocabulary. A great divide has opened up between the
way we speak of rocks and organisms and the way we speak of persons.
Vegetables belong to one discourse; souls to another. As scientists and
philosophers try to reconnect the two ways of thinking, it is worth look-
ing back at the history of vegetable life and the many attempts to find
one theory of life that spans vegetable, animal, and rational domains.
We have strong intuitions about what it means to be alive, but those
intuitions are constantly challenged by new discoveries. Microbiologists
have uncovered vast realms of tiny organisms living in extreme environ-
ments, and even within humans. Astrobiologists look to the stars and ask
whether still stranger forms of life might be out there (Hays et al. 2015).
Both have provoked us to revisit systematic questions about what it
means to be alive. Meanwhile, ethical debates, from genetic modification
to human cell cultures, from embryos to organ transplants, stretch the
meaning and boundaries of life. They have a profound impact on how
we understand biological fitness as well as ethical value. The history of
© The Author(s) 2018 1
L. J. Mix, Life Concepts from Aristotle to Darwin,
https://doi.org/10.1007/978-3-319-96047-0_1
2 L. J. MIX
vegetable souls provides a broader perspective, more options to consider,
and prospects for future research.
This book looks at the history of souls, purpose, and agency as they
have been applied to the non-human, non-animal living world. Such a
vast swath of reality now includes plants, fungi, protists, bacteria, and
archaebacteria (and perhaps viruses). All of these were traditionally
lumped together as “vegetables” and considered the lowest form of life.
Most thinkers believed that vegetables have less freedom, dignity, and
drive than animals, but more than mere minerals. Life was seen as a con-
tinuum, stretching from the lowest lichen to the smartest man, and per-
haps beyond.1
Vegetable and animal souls were mortal and natural by most under-
standings of those words and fell into a middle category between the
non-living environment and human life. They were the province of nat-
ural philosophers, the precursors of modern scientists, as well as theo-
logians. Christians, Muslims, and Jews claimed—and still claim—that
humans have a special kind of soul, an eternal soul. That claim, however,
once came in the context of a larger theory of life. It came as one aspect
of a soul-theory that spoke to the life of plants and animals. We were the
“rational animal,” but no less animal for that. We lived among a variety
of living, ensouled things.
In the renaissance and Enlightenment, theories of life changed dra-
matically. Cartesian dualism pushed the human soul out of the natural
world, along with will, reason, and agency. Vegetable and animal souls,
meanwhile, disappeared. They were neglected in the humanities and
intentionally ejected from the natural sciences. Empiricists considered
them unknowable, along with formal and final causes. The move proved
tremendously successful in the development of modern biology, but it
prohibited any common understanding that would bridge human and
non-human life.
The medieval understanding of souls—as subsistent, immaterial
agents—will never fit with modern science. Aristotle’s picture, however,
1 From a twenty-first century perspective, I can object to both ends of this scale. Lichens
represent a sophisticated symbiosis of fungi, algae, and cyanobacteria. No matter how we
define “simple,” many simpler organisms exist. Likewise, I would object to the superiority
of men over women. I might even ask how we are to define humans as superior to other
multicellular organisms. I will return to these questions in part IV. As to animate life with
more dignity than humans, the traditional contenders were stars, planets, and angels.