ADAPTATION TO THE ANTHROPOGENIC ENVIRONMENT.
So far we have explained the heterogeneous distribution of animals and plants on earth by
adaptation to the planet’s vastly different environments. We have learned that organisms are
adapted to their non-living or abiotic environment (e.g., climate and soil of their environment)
and their living or biotic environment (as was illustrated in the various symbiotic relationships.)
However complex and surprising, the interactions in mutualism, competition, and antagonism
show organisms as exquisitely adapted to each other as they are to their non-living environment.
Humans have made a major impact on their environment and because the large human
population occupies every inhabitable corner of the continents, their influence on the other living
organisms is expected to be enormous. Many organisms have been driven from the human
environment (e.g., large predators) while others find benefit in the human habitat and, often
unintended, do well in human proximity (e.g., house mouse, cockroach, European house
sparrow).
Of particular interest are the relations that humans have with the organisms they have co-opted
for their benefit: livestock, pets, cereals, and crops. The results of these relationships are an array
of animals and plants precisely adapted to the whims and needs of the human environment.
DOMESTICATION.
Especially, over the last 10,000 to 5,000 years humans have domesticated a large number of
mammals (dog, sheep, goat, cattle, horse, cat, rabbit, etc.), birds (chicken, turkey, duck, goose,
canary, budgerigar, etc.), fish (carp, catfish, salmon), insects (honey bees, silk moth) plants
(cereal, vegetables, fruits), molds (e.g., button mushroom, bread yeast, beer and wine yeasts,
etc), and bacteria (yoghurt, cheese). Agriculture started in nine ancient centers of origin of plant
and animal domestication which were those regions to which the most valuable domesticable
plants and animals were native. For instance, the Fertile Crescent of Southwest Asia was home to
wild wheats, barley, peas, sheep, goats, cows, and pigs. The domesticated plants and animals
spread from their centers of origin to other parts of the world. And many of these other areas
proved much more productive when those valuable domesticates reached them.
Domestication of Animals.
Dogs. Dogs were domesticated from the grey wolf some say more than 50,000 years ago when
humans were hunter-gatherers (Table). Among the wolf population some individuals were less
afraid of the band of humans and started following them anxious for left-over foods. Perhaps
humans valued the presence of these wolfs as protection against other predators or support in
their pursuit of food. Perhaps, humans started to raise some of the wolf pups they found close to
their camps. Those pups which tolerated best human presence and handling received most food
and care and survived. These may have passed on their genetic traits that made them more
adaptable to human contact to their offspring. Over time, their lineage became the domestic dogs
of today. Domestication and adaptation to the human environment changed the gray wolf from a
dangerous predator to a loving family pet, the domestic dog.
Sheep, goat, and cows. Domestication of food animals, cereals, and crops started in earnest
about 10,000 years ago, at the end of the Paleolithic and the onset of agriculture. Sheep, goat,
and cattle (Table) were domesticated as major food animals very early on in the history. Initially,
herds of animals may simply have been driven together and been slaughtered over time. Those
individual cows, sheep, or goat that tolerated the confinement and human presence best may
have given birth to their offspring and their offspring may have been raised in the confinement,
extending the human food supply. Those that would reproduce in such conditions may have
become the stock of today’s domestic cattle, sheep, or goat. Sheep were domesticated very early
for the benefit of their wool, skins, as well as their meat and milk. Besides being a source of milk
and meat, cattle‘s most important contribution in these early times was their use in tilling the
land, which expanded farming land and thereby increased yield significantly. The ancestor of
domestic cows is the Aurochs, a massive herbivore native to most of Southwest Asia, Turkey,
and Europe. Domestic cattle is much smaller and, as is true for most domestic animals, has
significantly smaller brains than their wild ancestors. Aurochs survived in Europe until the late
middle ages with the last female killed by poachers in the early 1600s in a forest in Poland.
Species
Date
Location
Purpose
Hunting,
transportation,
companionship
Wool, meat, milk
Milk, meat
meat
Meat, milk, soil
fertilization, muscle
Hunting,
companionship
Dog (Canis lupus familiaris)
50,000 BC
East Asia
Sheep (Ovis aries)
Goat (Capra aegagrus hircus)
Pig (Sus scofa domestica)
10,000 BC
10,000 BC
9,000 BC
Cow (Bos primigenius Taurus)
8,000 BC
Southwest Asia
Iran
Near East, China
India, Middle East,
Africa
Cat (Felis catus)
6,000 BC
Near East
Chicken (Gallus gallus
domesticus)
6,000 BC
India
Southeast Asia
Horse Equus ferus caballus)
4,000 BC
Eurasian steppes
Turkey (Melagris gallapavo)
European Rabbit
(Oryctolagus cuniculus)
500 BC
Mexico, US
Milk, meat, muscle,
transport
Meat, feathers
1600
France
Meat, companionship
Meat, eggs, feathers
Horse. The mere finding of bone fragments at sites of ancient human dwellings may be
insufficient evidence for the domestication of an animal. However, common burial sites for
humans and their dogs or cats constitute strong evidence for the close relationship between the
two and the domestication of the animals. The earliest possible hints for the domestication of the
horse is the presence of what appears to be a set of post molds with remains of lots of horse
manure within the area (enclosure) defined by the posts in the vicinity of human dwellings. That
evidence dates back to 5,000 BC and was found at Krasni Yar, Kazakhstan. Accepted
archaeological evidence for horseback riding includes bit wear on horse teeth that has been been
found in the steppes east of the Ural mountains in Kazakhstan, dating to 3,500-3,000 BC.
Initially, horses were kept for both their meat and milk (as they still are in places of Europe and
Kazakhstan today). Evidence of horse milk was found at one archeological site in Kazakhstan in
the form of fatty lipid residues on the insides of ceramic vessels. Finally, the earliest direct
evidence of the use of horses as beasts of burden, in the form of drawings of horse-drawn
chariots, and the finding of chariots at burial sites dating from about 2,000 BC, in the Middle
East.
Cat. In sharp contrast to the dog, cats were not domesticated to look or act very different from
their wild ancestors (the Middle Eastern wild cat or Felis sylvestris lybica). Because a 9,500
year old graveside revealed remains of a human buried alongside a cat, historians believe that by
this time humans got personally attached to their feline friends. Cats probably did not take to
domestication as wolves/dogs did because cats have no social hierarchy that allows humans to
take the alpha role. The cats’ infamous dislike for small rodents made cats appealing to humans
especially during the early times of grain and cereal storage. Indeed, House mouse remains were
preserved with human stores of grain in Israel dating to 10,500 to 9,500 years ago at the dawn of
human agriculture and of permanent settlements. Trading pest-control for food and shelter, cats
eventually overcame their aversion to domestication, however, they are still not known for taking
orders from humans. In 2004, archeologists working on the Mediterranean island of Cyprus
discovered the 9,500 year burial of an adult human and a cat. Because cats are not native to
Cyprus, people must have brought them over by boat from the nearby Middle East. A 3,700 year
old ivory cat statuette sculpted in what is today Israel suggests cats were a common site around
early human settlements of that region. Artists painted domesticated cats from Thebes, Egypt
3,600 years ago providing the oldest evidence of a fully domesticated cat. Cats become “official
deity” of Egypt in the form of the goddess Bastet 2,900 years ago. A huge number of cats is
sacrificed and mummified in the god’s sacred city, indicating that the Egyptians were breeding
domestic cats. At the height of cat worship in Egypt, the Ptolemeic rulers (2,300 years ago)
maintained strict bans on the export of cats. The Tamara Maew (or “cat-book poems”, 13601767) was composed by Buddhist monks in Thailand and describes indigenous, natural breeds,
such as the Siamese (Wichien Maat), which arose largely without human intervention. Many of
the modern cat breeds were developed in England in the 1800s and in 1871 the first cat show was
held in the Crystal Palace in London and included human-made breeds.
Recent domestications. Other of the domestic animals were domesticated much later. By the
first century BC, people were using ferrets (and later dogs) to flush rabbits out of their holes in
the ground. French monks domesticated rabbits and raised them as a food source in the late
Middle Ages. The origin of domestic hamsters dates back to 1930 when a mother and her babies
were caught in Syria. At first, people recognized the value of hamsters in scientific experiments
and later as pets. European Hedgehogs were domesticated in the US as recently as the 1980s.
Not all animals (or plants) can be domesticated. Humans have tried to domesticate such
animals as elephants, zebra’s, and most large cats without much success. Some suggest humans
have succeeded in truly domesticating only 14 species out of 148 candidate large terrestrial
herbivores weighing 45 kg or more. It is proposed that for humans to domesticate an animal
species, the species usually satisfies the following criteria:
1. The right diet: Picky eaters have always made life difficult for their mothers, so one can
imagine the frustrations involved in keeping up with an animal with picky tastes. Humans
can only domesticate animals that thrive on cheap, accessible food. Hence, no domestic
anteaters.
2. Fast growth rate and short birth spacing: The species must grow at a fast rate for herders
and farmers to yield a timely return on the investment of raising it. One can only marvel
on the rate of growth and strength of cattle which in one year can grow to 600 – 800
pounds and can deliver a calf before her second birthday. Thus, elephants and gorillas
mature too slowly and have long intervals between birthing.
3. Friendly disposition: Vicious animals by definition don’t usually like it when humans
attempt to bring them in captivity and won’t let humans handle them. Industrial farming
pays much less attention to the ease of handling of farm animals then did farmers for
most of the recent history. Grizzly bears, rhinoceroses, and zebras have a bad disposition.
When European horse breeders settled in South Africa in the 1600s, they tried to
domesticate zebras. They gave up after several centuries because zebras are incurably
vicious, have the bad habit of biting a handler and not letting go until the handler is dead.
Second, zebras have better peripheral vision than horses, making them impossible to
lasso (they see the rope coming and flick their head away.)
4. Easy breeding: If the animal refuses to breed under the conditions human captors
provide, then obviously, its period under human control is short-lived. (Pandas and
cheetahs are reluctant to breed in captivity.)
5. Respect a social hierarchy: Most domesticated animals are by nature social animals
living in groups with a strict hierarchy. In such structures they follow the dominant
member of the group and it becomes easy for humans to establish themselves as leaders
of the pack. However, bighorn sheep and American antelope do not follow the leader.
The big exception here is the domestic cat which not now nor in origin was a social
animal and more tolerates than obeys its human hosts.
6. Won’t panic: Many animals freak out when they are restraint, kept in fences, or perceive
a threat. (This is a major problem, and often a fatal one, in zoos. Even routine veterinary
care may require that animals are restraint and this not infrequently proofs fatal for a
significant number of them.) Most deer panic easily. Cows and reindeer, on the other
hand, remain fairly complaisant and unflappable despite these conditions, making them
easier to domesticate. Note, that many of the domestic animals are prey animals. For such
animals to be restrained and lifted up is akin to be taken between the jaws of a predator.
Vietnamese potbellied pigs, miniature as they are when young, are absolutely panicked
when they are lifted up by their owner. The same is true for guinea pigs.
Domestication of Plants.
Many plants were domesticated for food. Some plants were cultivated for the strong fibers in
their stalks, which were used for such things as ropes and nets. Hemp (marihuana), one of the
ancient plants domesticated in India, is a multi-purpose plants: oil is obtained from its seeds,
fibers from its stalk, and the narcotic hashish from its flowers and leaves. Some plants were
domesticated especially for the production of narcotics. Tobacco, which was first used by
American Indian tribes for the preparation of a narcotic drink was only later used for smoking.
Also the opium poppy is domesticated solely for its narcotic. Only when humans reached a
sufficiently high level of culture did they begin to raise plants and animals for beauty or the
bizarre. Domestication of vegetatively reproducing plants, such as those with tubers, probably
preceded domestication of the seed plants (i.e., cereals, legumes, and other vegetables).
Corn. Maize (corn) (Zea Mays) is a plant of enormous modern-day economic importance as
foodstuff and alternate energy source. Scholars agree maize was derived from the a wild grass
called teosinte (Zea mays parviglumis) in Central America at least 900,000 years ago. The
process of domesticating maize radically changed it from its origins. The seeds of wild teosinte
are encased in hard shells and arranged on a spike with five to seven rows that shatter when ripe
to disperse its seeds. Modern maize has hundreds of exposed kernels attached to a cob which is
completely covered by husks and cannot reproduce on its own. The morphological change is
among the most divergent of speciation known on the planet, and it is only recent DNA studies
that have proven the connection between maize and teasinte. The earliest undisputed
domesticated maize cobs are from Guerrero, Mexico and dated about 4,200 BC. Starch granules
from domesticated maize have been found at sites as 9,000 BC. Eventually, maize spread out of
Mexico, probably by the diffusion of seeds along trade networks. It was used in the
Southwestern US by about 3,200 years ago, and in the eastern US beginning 2,100 years ago. By
700 AD, maize was well established up into the Canadian Shield. DNA studies suggest that
purposeful selection for various traits continued throughout this period, leading to a wide variety
of strains today. For instance, 35 different races of maize have been identified in pre-Columbian
Peru, including popcorn, flint varieties, and varieties for specific uses such as Chicha beer, textile
dyes, and flour.
Wheat. The two most common kinds of wheat in the world today are Triticum aestivum (bread
wheat) and accounting for some 95% of all the consumed wheat and Triticum turgidum durum,
which is used in pasta and semolina products. The origins of our modern wheat, according to
genetics, are found in the Karacadag mountains of southeastern Turkey. There in 10,000 BC two
types of wheat were domesticated: einkorn (T. monococcum) and emmer wheat (T. turgidum).
The main differences between the wild forms of wheat and domesticated forms are that
domesticated forms have larger seeds and a non-shattering rachis. Wild wheats bear their seeds
on top of stalk that spontaneously shatters, dropping the seeds to the ground where they can
germinate (but where they also become difficult for humans to gather). An occasional singlegene mutation that prevents shattering is lethal in the wild (because seeds fail to drop), but
conveniently concentrates the seeds for human gatherers. Once people started harvesting those
wild cereal seeds, bringing them back to camp, accidentally spilling some, and eventually
planting others, seeds with a non-shattering mutation became unconscientiously selected for
rather than against.
As a species becomes more and more domesticated, it changes. Domesticated species look
drastically different, become bigger or smaller, behave differently from their wild ancestors, and
often have different mating habits. Domesticated animals are more likely to mate year-round,
rather than seasonally, as they do in the wild. Domestication then changes an organism
profoundly including its genetic make-up from that of its ancestors so to allow humans to control
their growth, size, behavior, and breeding. As such, “taming” of individuals of a species differs
from domestication which forms a new species through the domestication process. For instance,
we can tame individual Indian elephants to work for us without altering their nature or select a
new species of domestic elephant.
Note, humans themselves have changed significantly as a result of animal and plant
domestication. For example, milk has changed our digestive system. Before animal
domestication, people naturally developed lactose intolerance as they grew into adulthood and no
longer needed a mother’s breast milk. However, when humans started raising livestock, they
started drinking more milk, and this has adapted our digestive systems to accommodate milk
throughout our lives. More profoundly, close proximity with animals exposed humans to animal
pathogens that, in turn, adapted to the human hosts and found in the crowded population centers
of the early settlements and cities a fertile ground to spread rapidly. This lays at the origin of
many deadly infectious diseases.
A PLETHORA OF ANIMAL AND PLANT BREEDS.
The initial domestication of animals and plants has led to a proliferation of different breeds or
races of each animal and plant species fulfilling every nutritional, economic, social, and esthetic
need of humanity. After the initial spread of livestock, cereals, and crops animals and plants were
bred in mostly isolated villages and urban centers and, because of the limited transportation
means, adapted to the unique properties and human demands of their region. Often, bizarre and
irrelevant traits were accidently included and maintained. Thus, all over the globe sheep, goat,
cattle, swine, horse, dogs, chickens, etc… developed with unique characteristics. Up to the 1940s
nearly every small village of Europe housed a distinct breed (or race) of chicken, pigeon, or
rabbit recognizable from the breeds of neighbouring centers. Breeds of sheep, goats, and cattle
typified geographic regions. Many of the distinguishing traits of these breeds likely were
accidental to the selection for more utilitarian and economic properties of the animals (size, meat
taste, milk production, wool quality, strength, etc.) How did humans direct the adaptation of their
animals and crops to their particular needs? To adapt a given animal or plant species to a
particular human need required nothing more than patient and disciplined selective breeding.
Indeed, it was intuitively clear from antiquity that if one wanted smaller cattle one selected for
breeding both the smallest cow and bull and removed from the herd the larger animals (i.e., cull
the larger animals). Because traits are in part heritable, those parents would pass their smaller
stature to their offspring and before long the entire herd would be smaller than the ancestral
population. The more rigorously the selective breeding programs the faster the traits of the
population changed. Whereas breeding of livestock, horses, dogs, and poultry became very
purposeful in the 18th and 19th century and gained from developments in mendelian genetics
throughout most of the 20th century, selective breeding is now increasingly guided by progress in
molecular biology (E.g., crops resistant to herbicides and insect pests.)
The consequences of domestication and continuous selection to obtain plants and animals with
particular traits are so great that the differences between breeds of animals or varieties of plants
of the same species often exceed those between different species under natural conditions. The
traditional domestic animals and cereal and crop plants are now considered species distinct from
that of their wild ancestors. Moreover, most knowledgeable biologists on finding the fossilized
remains of the Chihuahua and the Great Dane would classify the two dog breeds as separate
species.