Domesticating humans
Did humans and dogs become domesticated at the same time?
Petroglyphs from Bushmen of South Africa illustrating an early hunt
with dogs. Painting taken from Vinnicombe, P. 1976. People of the
Eland: Rock Paintings of the Drakensberg Bushmen as a reflection of their life
and thought. Pietermaritzberg:
University of Natal Press. One-time rights.
April Holladay
Published on Monday, May 10, 2010 12:01 PM MST
Since humans domesticated dogs, causing actual genetic changes in the
canines, has there been a reciprocal genetic change in humans making us more
compatible with dogs? In other words, have dogs domesticated humans as
humans domesticated them? Lanney, Sandia Park, New Mexico, USA
It seemed
so logical — dogs domesticated humans in the sense that humans became unafraid
of dogs (although we continued to fear wolves). Dogs made life safer and easier for humans as dogs
learned to warn people about marauding predators and to herd animals. Why shouldn't dog-liking
people
prosper over other humans? Natural selection would favor 'dog people'
genes, the human gene pool would change accordingly and,
therefore, dogs domesticated people.
But I could find no supporting evidence in the literature. Maybe it's
true, but the only evidence I found is the tremendous number of people who now have dogs
as pets.
However, humans probably did become
domesticated (definition) about the same time
as small dogs. Here is the story, a conjecture, of how it might have
happened.
But finding any evidence that's survived 10,000 years is tricky. So, let's
start with the clearest evidence we have: a mammal's body size.
Biologists, anthropologists, and archeologists agree a mammal's body size
diminishes as a mammal becomes 'domesticated.'
The early stages of domestication of any mammal are "almost always
accompanied by a reduction in size of the body," writes researcher
Juliet Clutton-Brock of The Natural History Museum, London. In
fact, archeologists use body size as the main criterion to distinguish the
skeletal remains of domestic from the wild animals they dig up.
So, back to the problem: Have humans become domesticated? Human
bodies have become smaller since humans developed agriculture and
domesticated small dogs, about 10,000 years ago. (By the way, recent Swedish
and Chinese studies suggest humans domesticated large dogs even earlier — about
16,000 years ago — in southeastern Asia.)
Christopher B. Ruff and colleagues from the Johns Hopkins University School
of Medicine compared a representative sample of living humans with the remains
of 163 Pleistocene Homo sapiens (who lived about 100,000 to 300,000 years
ago) and found modern-human body mass averages about 10% less than the
early-human body mass.
So far, so good. Modern-human body mass has
shrunk relative to our Pleistocene ancestors.
About 10,000 years ago, perhaps two to three thousand people lived in this settlement of Tell es-Sultan
in Jericho near the Jordan River. They lived in round mud-brick huts
scattered over an area approximately one city block surrounded by the oldest stone
wall yet discovered. The people hunted and farmed the fertile, rich river land,
growing the first domesticated crops — emmer wheat, barley, lentil and chick
peas.
These people may have been among the first
domesticated humans, although human domestication probably started well
before 10,000 years ago. Some small
wolves native to this Fertile Crescent land (the Levantine wolf) probably
scavenged the village garbage heap and,
eventually, became domesticated small dogs.
So, here's the conjecture for human and dog co-domestication:
Over the millennia, humans changed from roaming hunters to settled
farmers who lived in homes and villages. This profound cultural shift,
culminating about 10,000 years ago in the Fertile Crescent,
domesticated humans and their evolutionary pals, small dogs.
As the ice ages ended, people no longer needed large
bodies to stay warm. Also, people got smaller because they no longer
hunted large savage animals and lived nomadically in the open. Smaller
bodies took less food to feed and, therefore, were more efficient as long as the
smaller bodies could earn a living and stay warm. When lands warmed and people developed shelter and agriculture, their smaller bodies survived the
less-demanding living conditions. Humans
became domesticated.
Likewise, much the same forces acted on the small wolves of the Fertile
Crescent. As people settled in homes and villages, they often dumped their
garbage in one spot. Certain small wolves that were
barely surviving in their family packs (because of their runt size) could branch
out into a new niche and survive better. Those small wolves that
weren't scared of humans could sneak in and steal garbage. They began
to hang around the dumps.
This strategy gave these smaller wolves a two-fold advantage. They ate
better than they had in the wolf-family pack, and humans protected them from
their larger wolf cousins. Humans and dogs formed a proto-pack. Why
the protection? Because the small wolves barked to warn their canine pack (and,
incidentally, humans) that dangerous big wolves were around. Humans
appreciated the warning and became tolerant of the small wolves.
So the little wolves evolved to smaller size, more
tolerance of humans, and guard-dog behavior. They became domesticated.
Humans had become smaller at about the same time and now developed a
tolerance for guard dogs. In time, humans expanded dogs' duties by
selecting those so inclined to herd and guard domestic
animals.
But changing genes has many ramifications. Perhaps changing a species'
body size has the unintended consequence of changing how the species matures.
At any rate, dogs, humans, and other mammals domesticated about 10,000 years ago
(for example, pigs)
share changes in how they mature. All these animals become more immature
in appearance than their wild ancestors. This process is called neoteny:
the retention of juvenile characteristics.
These traits are the "criteria of domestication" and include "morphological
changes affecting the skeletons of early Middle Eastern domesticates (e.g.,
reduction in size and skeletal robusticity, cranio-facial shortening, and
declining tooth size)," says anthropologist
Helen Leach of the University of Otago in New Zealand. Furthermore:
"These changes also occur in some human populations starting in the Late
Pleistocene."
Thus, humans meet the criteria of domestication, as do dogs. The two
species co-evolved and became domesticated at about the same time due to the
effects of their joint environment and life style. People now farmed in
one place (instead of roaming in search of game), lived in man-made homes
(instead of surviving the greater hardships of outdoor life) and dumped garbage
in one place. Dogs ate the scraps and sounded the alarm when predators
threatened them and their new partners — people.
Credit for this conjecture goes to
Helen Leach, biologist
Melissa M. Gray of
UCLA, zoologist
David W.
MacDonald of Oxford University and molecular biologist Carlos Driscoll of
the Cancer Institute, among others.
When I checked with Driscoll regarding the human-dog domestication conjecture
that he had alluded to in Top dogs: wolf
domestication and wealth, he emailed back yet a different theory: Human
domestication happened when humans became "self-conscious." We will
learn details when he publishes
a paper on the topic.
This column's rendition of Leach's, Gray's and MacDonald's theory on human
domestication is a simplification. Leach, however,
emails it covers "a complicated topic very well."
Clutton-Brock comments on the Jericho photo: "Jericho is only one of a very
large number of early Neolithic sites in western Asia where there is evidence
for the beginnings of livestock husbandry." She also says, "humans were living
in settled communities long before 10,000 years ago."
Leach agrees this column's rendition may compress events more than evidence suggests (for
instance, some human groups began to adopt a diet increasingly dependent on wild
grains and pulses, "millennia" before domestication of plants and animals is
apparent and the Levantine wolf also began its skeletal changes before
agriculture and sedentary village life became well established). But that
doesn't "affect the main points" of the conjecture tale, she says.
More exploring:
Can a domestic cat be trained as well as a dog? WonderQuest, 8
March 2010
Further Reading:
A
Natural History of Domesticated Mammals by Juliet Clutton-Brock, The
Natural History Museum, London.
Body
mass and encephalization in Pleistocene Homo by Ruff CB, Trinkaus E,
Holliday TW. Nature. 1997 May 8;387(6629):126-7.
Human Domestication Reconsidered by Helen M. Leach,
Current Anthropology Volume 44, Number 3,
June 2003
Top dogs: wolf
domestication and wealth by Carlos A. Driscoll and David W Macdonald,
Journal of Biology, 24 February 2010
The
IGF1 small dog haplotype is derived from Middle Eastern gray wolves by
Melissa M. Gray, Nathan B. Sutter, Elaine A. Ostrander and Robert K. Wayne,
BMC Biology, 24 February 2010.
mtDNA Data Indicate a Single Origin for Dogs South of Yangtze River, Less Than
16,300 Years Ago, from Numerous Wolves by Zhang Yaping and others,
Molecular Biology and Evolution, 1 September 2009.
(Answered 10 May 2010)
Readers' Answers
- Domesticating animals is the process whereby you breed an animal and
take the one that is the least aggressive and repeat. This influences the
genetic makeup of the animal to be less aggressive. When we domesticate
animals, we are not really changing our genetic makeup in any way. However,
one could argue that if you are a cat person or a dog person that you will
likely end up influencing your offspring's genetic makeup by mate
compatibility.
Shaun, Somewhere, World
- As much as I would love to believe that dogs did change humans as we
changed dogs, I would have to say no, they have not. I'm sure that
emotionally dogs can change human's characters and such, but not genetically.
The reason dogs have changed genetically would be because we bred them
together to try and make a prettier, healthier, smaller, or bigger dog than
before.
Nikole, Minneapolis, Minnesota, USA
- The best answer is to question the question: The implication that
human behavior follows from genetics and even from
specific genes has no scientific basis and this train of inquiry leads
to eugenics and the resulting horrors. The canine question is valid but actual genes are not modified, it is
selective breeding in which
desirable features are retained. Domestication was
studied
in Russia where wild foxes selected for their docility exhibited dog-like
behavior after very few generations.
Ilan Vardi, Neuchatel, Switzerland.
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April Holladay lives in Albuquerque,
New Mexico. Her column, WonderQuest, appears every second Monday of the month
on WonderQuest.com. To read April's past columns, please visit her
website . If you have a question for
April, visit this
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