Domesticated: Evolution in a Man-Made World

483 Pages·2015·4.77 MB·English

by  Richard C. Francis

CONTENTS
Preface
CHAPTER 1
HOUSE FOX
CHAPTER 2
DOGS
CHAPTER 3
CATS
CHAPTER 4
OTHER PREDATORS
CHAPTER 5
EVOLUTIONARY INTERLUDE
CHAPTER 6
PIGS
CHAPTER 7
CATTLE
CHAPTER 8
SHEEP AND GOATS
CHAPTER 9
REINDEER
CHAPTER 10
CAMELS
CHAPTER 11
HORSES
CHAPTER 12
RODENTS
CHAPTER 13
HUMANS—PART I: EVOLUTION
CHAPTER 14
HUMANS—PART II: SOCIALITY
CHAPTER 15
THE ANTHROPOCENE
EPILOGUE
APPENDICES
Appendix A to Chapter 5:
FROM THE MODERN SYNTHESIS TO AN EXTENDED SYNTHESIS?
Appendix B to Chapter 5:
GENOMICS AND THE TREE OF LIFE
Appendix to Chapter 7:
FROM LANDRACES TO BREEDS
Appendix to Chapter 10:
WHAT’S IN A GAIT
Appendix A to Chapter 11:
HORSE EVOLUTION
Appendix B to Chapter 11:
GENEALOGY OF HORSE BREEDS
Appendix to Chapter 12:
THE EPIGENETIC DIMENSION
Appendix to Chapter 14:
EVOLUTIONARY BIOLOGY, EVOLUTIONARY ANTHROPOLOGY, AND EVOLUTIONARY
PSYCHOLOGY
Appendix to Chapter 15: THE CONTROL OF FIRE AND ITS CONSEQUENCES
Acknowledgments
Notes and References
Index
For Andrew
DOMESTICATED
PREFACE
WITHOUT OUR DOMESTICATED ANIMALS AND PLANTS, human
civilization as we know it would not exist. We would still be living at a
subsistence level as hunter-gatherers. It was the unprecedented surplus calories
resulting from domestication that ushered in the so-called Neolithic revolution,
which created the conditions for not only an agricultural economy but also urban
life and, ultimately, the suite of innovations we think of as modern culture. The
cradle of civilization is, not coincidentally, also the place where barley, wheat,
sheep, goats, pigs, cattle, and cats commenced a fatefully intimate association
with humans.
At the onset of the Neolithic revolution, an estimated 10 million humans
inhabited the earth; now there are over 7 billion of us. The human population
explosion has been bad for most other living things, but not for those lucky
enough to warrant domestication. They have thrived quite as much as we have.
Since the Neolithic, extinction rates have been 100–1,000 times those of the
previous 60 million years. Among those lost were the wild ancestors of
domesticated species, such as the tarpan (horse) and auroch (cattle), but no
domesticated species has ever become extinct. The wild ancestors of camels,
cats, sheep, and goats are teetering on the brink of oblivion; their domesticated
descendants, though, are among the most common large mammals on earth. In
an evolutionary sense, it pays to be domesticated.
The success of domesticates comes at a price, however, in the form of
increasing evolutionary submission. We humans have largely wrested from
nature control of their evolutionary fate, which, it turns out, renders
domesticated creatures uniquely informative for those seeking to understand the
evolutionary process. Indeed, domesticated creatures provide some of the most
dramatic examples of evolution in the world today. Even a creationist
recognizes, at some level, that the transition from wolf to dog is an evolutionary
process. That is why the “artificial” selection for particular traits in domesticated
breeds—from dogs to pigeons—figured so prominently in Darwin’s argument
breeds—from dogs to pigeons—figured so prominently in Darwin’s argument
for an analogous process that he called “natural” selection.
The fact that wolves, which competed with and even preyed on Paleolithic
humans, were the first animals domesticated is testimony to the power of
humans as both a conscious and unconscious evolutionary force. And throughout
most of the domestication process for dogs and other mammals, the role of
humans as an unconscious evolutionary force was paramount. For that reason,
the distinction between natural selection and artificial selection is actually quite
blurry. As we will see, the domestication process was often initiated by the
domesticated animals themselves, when they sought, for various reasons, human
proximity. This process of self-taming occurred primarily through ordinary
natural selection. The sort of conscious selection we call artificial selection came
only much later in the domestication process. There is a large gray area of
transition between natural selection and artificial selection, in which humans
became an increasingly important but only partly conscious component of the
selection regime.
The combination of natural and artificial selection has proved very powerful
indeed. The size range of domestic dogs—from Chihuahuas to Great Danes—far
exceeds not only that of wild wolves but that of the entire canine family (wolves,
coyotes, jackals, foxes, etc.), both living and extinct, which originated in the
Oligocene epoch nearly 40 million years ago. In a mere 15,000–30,000 years the
selection imposed on dogs by their association with humans has caused
evolutionary alterations never experienced in the canine family during the
previous 40 million years.
Evolutionary modifications of dogs by humans extend to many other traits as
well, including coat color and skeletal modifications. Skull shape variation in
domestic dogs exceeds not only that of all other canines combined but also that
of all other carnivores—the taxonomic group of families that includes canines,
cats, bears, weasels, raccoons, hyenas, civets, seals, and sea lions—combined.
The effects of human selection on dog behavior have been no less dramatic.
Most notably, domestic dogs have an evolved capacity to “read” human
intentions. For example, they can interpret human gestures, such as pointing, to
locate distant food items. Wild wolves cannot do this. In fact, dogs are much
better at reading human intentions than are our closest relatives, chimpanzees
and gorillas. So in some ways, the social cognition of dogs more closely
resembles that of humans than does that of the great apes.
The human influence on the evolution of other domesticated creatures is only
slightly less impressive. The placid hyper-uddered Holstein cow does not much
slightly less impressive. The placid hyper-uddered Holstein cow does not much
resemble its wild ancestor, the noble and fierce auroch, nor do Merino sheep
much resemble the mouflon, their wild ancestor, though in both cases the
domesticated and wild forms share a common ancestor only 10,000 years ago.
That’s a lot of evolution in a very short period of time.
Since domestication is an accelerated form of evolution, it is an ideal subject
by which to nurture the intuitions and hence the understanding of nonbiologists
as to how evolution works. Evolution is a historical process, but most evolution
involves timescales that are hard for the uninitiated to digest, much less intuit,
given the limitations of the human mind. Domestication, however, occurs over
more comprehensible timescales. Dog breeds such as the English bulldog, for
example, have evolved extensively in just the last 100 years. It is therefore
possible to connect human history, prehistory (5000–30,000 BP), and
evolutionary history in a more or less seamless way. This is sometimes referred
to as “big history,” though I prefer “deep history.” This big or deep historical
dimension provides the backdrop for the main themes that will concern me
throughout.
The predomestication history—the deepest part of the deep history—is, of
course, the province of evolutionary biology, specifically the branch of
evolutionary biology concerned with reconstructing the genealogical
relationships on the tree of life, which is called “phylogenetics.” Much of what
we know about the period connecting predomestication history and written
history comes from the burgeoning field of zooarchaeology, which combines
expertise in ancient human cultures, animal biology, and natural history. The
more recent history of domestication, for which we have written records,
concerns the phase during which humans have assumed the most conscious
control. This phase, which is still ongoing, is one of unprecedented change, for
good and ill.
While this historical backdrop is, I hope, interesting in and of itself, it is also
essential if we are to understand how evolution works. Domesticated creatures
are familiar to one and all. As such, their transformations are easier to perceive
and appreciate—a prerequisite for my main aim here, which is to consider some
recent and current developments in evolutionary biology through the lens of
domestication.
We can consider each case of domestication as a sort of natural experiment
in evolution. By “natural experiment,” I mean a case that is ideally suited for the
study of evolution but was not planned as such. We also have natural
experiments in reverse domestication, called feralization. The dingo is one such
experiment. Transported to Australia approximately 5,000 years ago by proto-
experiment. Transported to Australia approximately 5,000 years ago by proto-
Polynesians, dingoes transformed from pets into the apex predator of the
outback. In the process, they evolved into more wolflike creatures; indeed,
dingoes provide interesting contrasts to both wolves and domestic dogs.
In addition to these natural experiments of past domestication and
feralization events, we now have actual ongoing scientific experiments in
domestication—that is, attempts to experimentally replicate the domestication
process for the sole purpose of illuminating the evolutionary processes at work.
Though each case of domestication involves some interesting and unique
peculiarities, some general themes emerge that are equally interesting and
significant for evolutionary thought. Among the most noteworthy and revealing
of these themes is that domestication has unintended consequences. It seems
that, in selecting for one trait, humans invariably inadvertently affect other,
seemingly unrelated traits. It turns out that such by-products are a general feature
of evolution by natural selection. They can act as a brake on the evolution of a
trait under selection and/or create new evolutionary opportunities.
Another theme is that the amount of change in phenotype (which includes
behavioral, physiological, and morphological traits) does not correlate closely
with changes in the genome (genetic makeup). For example, large physical
changes in domesticated animals often involve remarkably few genetic
alterations. The genetic distance between dogs and wolves is tiny compared to
their physical distance. This is no less true of pig, cow, or horse, which brings us
to the third theme: that the human environment has some remarkably consistent
evolutionary effects on creatures spanning the vast genomic (and hence
evolutionary) distance between horses and dogs.
The paramount theme of this book, though, is the conservative nature of the
evolutionary process, even, as in domestication, when it occurs with the most
rapidity. In most popular accounts of evolution, the creative side of evolution
gets all of the attention. This is part and parcel of the adaptationist program, in
which the goal is to demonstrate the diverse—and seemingly boundless—ways
in which organisms respond adaptively to environmental challenges. But
adaptive change is far from boundless; it is actually quite restricted, channeled
by the previous evolutionary history of an organism. In fact, adaptive change is
restricted to tinkering at the margins of what has previously evolved. The
Pekingese is a tinkered wolf, not redesigned wholesale from its wolf ancestors.
Two recent developments within evolutionary biology in particular have
brought the conservative side of evolution to the fore: genomics and