Human Evolution
Sources:
Miller, Living in the Environment, Ch. 4
J. Diamond, The Worst Mistake in the History of the Human Race
Bronowski, J. The Ascent of Man
Human Evolution: The Current State of Affairs and So Near Yet So Far - S.J. Gould
New York Review of Books
Scientific American, Jan. 2003 – An Ancestor to Call Our Own.
The Greening of the World - Clive Ponting
The Great Leap Forward by Jared Diamond in text Technology and Society
GENERAL FACTORS AFFECTING HUMAN HISTORY
Large scale geological and astronomical forces over long periods of time have had
effects on human life:
Plate tectonics - movement of land masses caused by convection currents in the molten
core of the earth.
Where the plates meet there is disruption in the form of earthquakes and volcanoes.
Many natural disasters have essentially devasted human civilizations/settlements.
Thera may have destroyed the Minoan culture in Crete and Vesuvius destroyed
Herculaneum and Pompeii. An earthquake in Shensi province in China in 1556
killedover 800,000 people. More recently, Lisbon in 1755 and Tokyo in 1923 that
killed tens of thousands.
Continental drift - (dates vary greatly)
Pangaea - somewhere around 225 million years ago (Permian period), various
land masses had collided forming a large continent surrounded by the Panthalassa
ocean. The Appalachian mountains in the US were formed by the collision
between north america and Europe. Ten different orders of reptiles, from
crocodiles to dinosaurs dominated primitive mammals. Appearance of birds.
200 million years ago (Triassic period) earth had two supercontinents: Laurasia
(north America, Europe and Asia) and Gondwanaland (south America, Africa,
India, Australia and Antarctica) divided by the Tethys Sea. Separates species on
the two continents, flowering plants appear. Southern continents situated over
south pole, causing glaciers in what is now Brazil and South Africa, while
Laurasia was in the tropics. North American broke from Europe about 80 million
years ago, the last 80 million years has seen the creation of the Atlantic ocean.
65 million years ago - further separation of continents. South America and Africa
separates during last 100 million years, although Africa was still touching
Euroasia until 40 million years ago. Northern animals could spread south, and
African mastodon and elephant expand range, even to New World. India as island
moves upward. Break between Australia and Antarctica occurred in last 60 million
years. Expansion of mid-ocean ridge floods continental margins. Mammals
diversify and come to dominate reptiles.
Today - India moving into Asia, uplifts the Himalayas and Tibetan plateau (rise a
meter every century). The Mediterranean Sea is the remnant of Tethys Sea (plate
boundary between Europe and Africa). rifts inch open in East Africa. Coastal
California moves northwest and 40 million years from now will be an island.
Arabia and Africa are separating, creating new sea bed in the Red Sea. Stress of
converging plates causes volcanoes, like in the Pacific Rim.
Continental drift has had a profound effect on human history. Determined distribution
of resources and distribution of flora and fauna on the continents.
Coal, oil and natural gas come from the decomposition of the vast tropical forests
present about 250-300 million years ago.
Some animals have evolved in isolation and some have been driven to extinction
by competitors when suddenly brought into contact with other parts of the world.
e.g. marsupials had a worldwide distribution about 80 million years ago.
Replaced in Europe by mammals when continents drifted apart. Survived in
South American until it joined with North America about 30 million years ago.
Still live only in isolated Australia.
e.g. Isolation of Americas from the Eurasian landmass meant that animals
domesticated in Europe and Asia such as sheep, goats, cattle and horses were
not present. Influenced both agriculture and transport. Americans knew the
concept of the wheel, but could not use it effectively with drought animals.
Climate: a fundamental force in shaping human history. Climate variations affects crop
yields, and in the long term have influenced the ability of humans to settle in certain
areas of the world, have influenced the way plants and animals are distributed and have
placed limits on the types of crops that can be grown. The ice ages were created due the
concentration of land masses down from the north pole, which allowed glaciers to creep
down from the north. The south pole is basically isolated by water, and so glaciers could
not form down there. The ice ages have dominated the earth's climate for the last 2 and
a half million years.
Causes:
1.
2.
3.
4.
Position of the continents (see above)
Steadily increasing solar output
Carbon dioxide and methane in atmosphere
Three astonomical cycles affecting the earth and its orbit round the sun.
Earth's orbit varies from an elipse to a nearly perfect circle every 90-100,000
years. At present orbit is becoming more circular, thereby decreasing the
difference between the times when the heat from the sun falling on the earth is
at its maximum and minimum.
The timing of the earth's closest approach to the sun is completed every 21,000
years. At the moment the earth is nearest to the sun during the northern
hemisphere winter. Reduces the impact of seasonal climatic change in the
north whilst increasing it in the southern hemisphere.
The third cycle affects the tilt of the earth, which varies over a period of about
40,000 years. At the moment the tilt is decreasing which again reduces the
difference between the seasons.
These cycles affect the distribution of the sun's energy falling on the earth. The
current closeness of the continents in the northern hemisphere to the pole is of
crucial importance because only a 2 per cent drop in heat from the sun during the
northern summer can initiate glaciation. Cool summers allow winter snow and ice to
survive to the next winter and the growing snow cover causes further cooling by
increasing the reflectivity of the earth's surface. Further reduces the temperature in
the northern hemisphere leading to a rapid increase in the extent of ice sheets and
glaciers. This does not work in southern hemisphere, because of insufficient land
mass.
The series of ice-ages has dominated the earth's climate for the last 2 and a half
million years. There has only been about 250,000 years between glaciers.
What Makes Us Human?
Humans are characterized by a particular morphology, or structure. We use the word
“morphology” to refer to our form at any given moment, since our present form is the
result of a life of development involving biological structure taking on form via
couplings with the environment. We are dependent for our survival on complex and
interrelated physical, chemical and biological processes.
Our species form is the product of at least 5-8 million years of evolution along a
distinctive track, this being the estimated length of time we have been evolving
separately from other primate species.
All species are unique, and are defined by a pattern of variables. There is not just
one characteristic that makes us human, but a number of combined
characteristics - upright posture, large brain, opposable thumb, a flat face, a
unique vocal apparatus, etc. We cannot also forget the physico-chemical aspects
that make us unique, etc.
What we are today is the result of multiple adaptations to certain environments
throughout our evolutionary history. We have carved out a niche for ourselves - a place
within all the physical, chemical, and biological processes and we hold certain
interrelationships with other organisms. We belong to communities of organisms, and
our place in these communities is something that must be continually maintained.
The environment to which we have adapted provides the essential foundation for
our viability as organisms. It influences our behavior by providing constraints on
our development as individuals and patterns of interaction with each other, or
our social structure.
The particular way in which we live in the world is the result of several interdependent
factors:
1. Our morphology - determines what we need to survive as biological
organisms; nutrients, air, water, etc. We also require social stimulation
for the proper functioning of our nervous system.
Our physical shape determines how we walk through and touch the
world - upright posture, manipulating hands, eyes in front, flat face, face
to face communication. A large brain has made it possible for us to
attend to the world in more complex ways, allowing for more complex
behaviors such as planning and controlling our actions.
2. Social organization - our morphology necessitates development within a
social context. In the absence of any particular physical skills, our
primary means of adapting has been the development of group
cooperation. This includes all the mechanisms by which we get what we
need from the world - our economics.
3. Ecology - in this context, environment. We live in a structured environment,
first "natural" characteristics and then "human", "artificial"
characteristics. The need to survive in the world has given us the
morphology that characterizes us today. We now live in a human,
artificially constructed world - structured in time, physically organized,
objects of daily use.
Continuities Between Humans and other Living Organisms
(Source: S.J. Gould; A matter of degree. In Ever Since Darwin)
From the beginning of recorded history, we find a concern with what makes humans
distinct from other living organisms. This is really a search for human nature, for our
essence. We have had a hard time accepting that we are part of the living world. A great
many suggestions have been made over the centuries. Some popular ones have been the
soul, a mind, the use of tools, language, and our intelligence.
One favorite approach to this question during the last 150 years has been to compare
ourselves to our closest relatives, the chimpanzees and gorillas. Strange as it may first
seem, the differences between ourselves and our closest evolutionary relatives are
minimal. We share every brain and bone structure with a chimpanzee. In fact, a bit over
98% of our genes are the same, and yet they look quite different.
A debate raged in England in 1861 about possible differences in brain structure
between chimps and humans between T. Huxley and R. Owen. Owen claimed that
there was a small convolution in the hippocampus minor - a small structure in the
limbic system of the brain. Huxley claimed that such a structure did not really
exist. Huxley won.
Possible criteria for asserting our uniqueness.
Popular distinctions:
1. Functional or behavioral differences
When asked what the differences are between ourselves and chimpanzees
most people come up with examples of functional or behavioral
differences. These include such things as intelligence, tool use, rationality
or logical abilities, language, morality, a mind, or self-awareness.
In every one of these areas differences exist but these differences are not
differences in kind, they are differences in degree. Chimps show
elementary aspects of all these characteristics, if raised under the
appropriate conditions.
2. Structural or Morphological (form) differences
Again, differences between ourselves and chimpanzees exist but they are
not qualitative differences (of kind) but are qualitative (degree)
differences. A chimp has every brain structure we have – but our brain in
larger. We share every single bone, but their shape differs.
We can point to a number of characteristics which mark a difference
between the two species and which seem to have played a very important
role in human evolution – e.g. an upright posture, an opposable thumb, a
round, bulbous cranium (allowing for a larger brain), a vocal apparatus
which makes speech possible.
3. Genetics
There are very few genetic differences as mentioned above. We share over
98% of our genes with chimpanzees. If we thought that each organic trait
(like an upright posture) is caused by a single gene we could reconcile the
paradox; many differences in form and function would reflect many
differences in genes. But then there should be many more gene differences
than there are, given the differences in form and function.
In biology we can define Sibling species, which are similar in morphology
but separately reproduce. We also define Congeneric species - pairs of
species placed in same genus but different morphologically.
Chimps and humans are much closer than either category.
Question: what do those genes that make up the 1 or 2% difference do?
Answer: certain genes must have big effects on entire organism. These few
genes must be creating a great divergence. The biggest effects could come from
genes that control the regulation of timing of when things happen in the
developing organism. Humans may have had mutations of the regulatory
system.
All cells in our body have the same genes in their nucleus. Liver and skin have
the same genes – so what makes them different? The difference is in their
alternate paths of development. Genes are turned on and off at different times
during development depending on their location in the embryo and fetus.
perhaps it is the timing of when events occur and the changing sensitivities of
the organism at different points in development, that makes the differences
between us and a chimpanzee. The turning off and on of genes is a complex
process involving all sorts of chemical, genetic, and more general higher level
factors. The effect of a single gene or chemical early on can have a great effect
when the developing system is simple. Are the differences then due to the timing
of gene expression during development?
Could regulatory genes be the difference between ourselves and chimpanzees?
If so, they would have to account for the major important human characteristics:
1. a large brain
2. an upright posture
3. speech
4. the technological means to adapt to hostile environments
Delayed Development
One thing we might note about humans is that there appears to have been a
retardation in developmental rate. Compared to other primates, we are physically
less developed at birth, we mature later, and live longer.
For example, compare the state of brain development at birth for different primates:
Rhesus monkey
Chimpanzee
Man
- 65% of final size
- 40.5% of final size, 70% in first year.
- 23% of final size, 70% at third year.
30% of the human's total life span is spent growing.
One consequence of this is that learning is enhanced by our delayed maturation.
This is important for an animal that is not particularly strong, swift or well designed.
Nor do we reproduce rapidly. Learning is enhanced by extending childhood and
delaying sexual maturation which leads to a desire for independence. We are tied for
a longer time to our parents which makes for greater learning and the strengthening
family/social ties.
A lot of our advantage is related to the size of our brain. It also must have to do with
the way it functions. Over 70% of the final growth of our brain occurs outside the
womb in a human world. This is absolutely necessary for normal brain functioning.
We would not be human if we were not raised in a human social context.
(Note that there have been unfortunate cases of children who are normal
physically but who have been raised by ill parents in closets or attics. These
children, without social and physical stimulation, do not grow up to be what
we call human. They lack language, are of low intelligence, and have little
self-awareness. Being human requires a human developmental context, it is
not “given” in our biology. Our biology, while a necessary condition for being
human, is not sufficient.)
Let’s take a closer look at the human state at birth….
(Source: S.J.Gould; Human Babies as Embryos. In Ever Since Darwin)
Newborn animals may be characterized as falling into two general types (work
of Adolf Portmann):
1. altricial species – these species have a brief gestation period (gestation
means the time the female is pregnant) and large litters of poorly
developed young (tiny, hairless, helpless, unopened eyes and ears),
short life spans, small brains (relative to body size), and low level of
social behavior.
Altricial species may correlate with marginal, fluctuating and
unstable environments in which animals do best by high reproductive
rates.
2. precocial species – these species have long gestation periods, long life
spans, large brains, complex social behavior, give birth to a few well
developed babies that are partially capable of defending themselves
at birth.
Precocial species may correlate with stable, tropical environments.
Predictable resources and so invest energy in a few will developed
individuals.
How would you characterize humans? We seem to be a mix of these two types.
Our young are relatively helpless at birth compared to other primates, and yet
we seem to fall in the precocial catetegory in other respects.
The answer seems to lie in the fact that human development has been retarded
but our gestation period has not. If we examine the relationship between primate
gestation period and the total life span of an individual species we find a ratio
that is the same for all primates. The longer the life span the longer the gestation
period. However, this relationship does not hold for humans. Our gestation
period is slightly longer than other primates but quite short in relation to our life
span.
Total Life Span
Gestation Period
Apes _________/__________________
Humans _________/___________________________________________________
Chimpanzees for example have a life span of roughly 65 years and the females
have a gestation period of about 8.5 - 9 months and usually have a single baby at a
time; twins are rare. They are fully grown and able to reproduce at 12-13 years
old.
If we had a gestation period of the same life span proportion as other primates, our
females would be pregnant for 18 months.
Consequently, we are born too early. This explains why we are both altricial and
precocial. We are born as fetuses, and still have a lot of growing to do after we are
born.
Why has gestation stayed short? A likely reason is that the female birth canal is
too small, restricted in size by our upright posture. As it is, the birthing process in
humans is not too easy, our babies are large compared to size of the female. As it
is, an infant’s head has to be compressed so that it can pass through the birth
canal. If development occurred later, after the skull plates had become fused, the
baby could not pass through the birth canal. (the “tight squeeze” hypothesis).
Fetal size is near its limit in our species.
Neoteny (“holding youth”)
(Source: Gould; The child as man's real father. In Ever Since Darwin)
The idea of neoteny is that because our development has been delayed, we spend more
of our time in the world as infants, and because of this longer development time,
juvenile primate characteristics could have been selected for in evolution. Those
characteristics would have been retained that make human adults more adaptive.
"Juvenile features are a storehouse of potential adaptations for descendants, and
they can be utilized easily if development is strongly retarded in time...In our
case, the "availability" of juvenile features clearly controlled the pathway to
many of our distinctive adaptations.” The slowdown or retardation of
development does not guarantee the retention of juvenile characteristics. But it
makes them available for selection.
If we compare ourselves to primates, especially the gorilla or chimpanzee, we find that
we share certain characteristics with infant apes. The apes lose these characteristics as
they grow up – we retain them. We can identify at least 20 such characteristics, 6 of
which are listed below.
Characteristics we share with juvenile stages of other primates
1. Rounded, bulbous cranium – Infant apes have a round head, but the brain grows
much more slowly than rest of the body so the skull is lower and relatively smaller
in adults. We have retained our rapid fetal growth rate and the brain grows faster.
2. Juvenile face – Infant apes and humans have a straight facial profile, with small
jaws and teeth, a weak brow ridge. Jaws of juvenile apes grow more rapidly than
the rest of the face, forming a pronounced muzzle in adults.
3. Position of foramen magnum - the foramen magnum is the hole at base of skull
where the spinal column enters the head. In humans this hole is pointing
downward, with the skull on top of the backbone and the eyes directed forward.
Infant apes share this characteristics, but as they grow this hole moves toward the
back of the skull so their natural posture is one of walking more or less on all
fours.
4. Skull sutures – In humans there is late closure of the skull sutures and delayed calcification of the skeleton. This is noticed in the soft spot in the head of newborn
humans, where the bones are not yet closed over the brain. It allows for postnatal
expansion of the brain. Fingers are cartilaginous at birth.
5. Vaginal canal – In humans the ventral position (facing forward) makes face-toface copulation possible. In other primates it rotates towards the back as the
animal grows up, so that their natural posture for sex is from the rear.
6. Big toe - Our big toe is strong and unopposable. In most primates the toe begins as
ours and later rotates to the side and opposes others for efficient grasping. For us a
strong toe creates a stronger foot for walking upright.
These are retarded characteristics (neoteny) but there are more advanced characteristics
as well – such as our long legs and large brain.
To some extent our organs evolve separately in response to different adaptive
requirements. This is called mosaic evolution.
Does this mean that if we lived longer we would grow into apes?
No. But the idea has had its defenders. A satirical story was written on this theme by
Aldous Huxley (author of Brave New World). The story was called After Many a
Summer Dies the Swan:
An American millionaire, Jo Stoyte, sets out to purchase his immortality. His
hired scientist, Dr. Obispo, discovers that the fifth Earl of Gonister has, by
daily ingestion of carp guts, prolonged his life well beyond 200 years. They
rush to England, break into the earl's well guarded estate, only to discover that
the Earl and his lover have grown into apes.
The truth about our evolution is out - we evolved by retaining the
youthful features of our ancestors (neoteny - "holding youth")
"A foetal ape that's had time to grow up," Dr. Obispo managed at last to say.
"It's too good!" Laughter overtook him again....Mr. Stoyte seized him by the
shoulder and violently shook him..."What's happened to them?" "Just time,"
said Dr. Obispo airily...the foetal anthropoid was able to come to maturity...without moving from where he was sitting, the Fifth Earl urinated on the
floor.
The Emergence of Humanity
(See Ch. 1 "Lower Than the Angels" in The Ascent of Man by Jacob Bronowski)
Origins in Africa - from Ethiopia to South Africa
Some 3,000,000 years ago.
The earliest fossils are found in the savannah country that stretches out across
Northern Kenya and South West Ethiopia near Lake Rudolph. The Great Rift
Valley along the river Omo. 4 million years of thick sediments.
The fossils of animals are similar to those of animals today. Humans have
changed more than animals - why? Not because they were better hunters
- the hunting animals are basically the same.
Because humans were not well adapted to their environment. Being well adapted
traps a species - change does not occur. Human evolution began when Africa's
climate changed to drought - lakes shrank, forests changed to savannah.
Walking upright - man's foot two million years ago was basically the same as
today. Standing upright occurred when we moved from the forest to the
savannah - looking out over the tops of bushes. This freed the hands for other
tasks than walking, like carrying things.
Walking upright brought about systemic changes in the human morphology. The
head has changed a great deal - probably a by-product of an upright posture.
The following timeline summarizes most of the fossils we have discovered that related
to human evolution. There are various interpretations of how these fossils fit together.
For a discussion of this issue, you may visit the following websites:
Becoming Human Documentary
Origins of Humankind Website
HUMAN EVOLUTION – THE FOSSILS
There have been about 20 human and hominid (human-like) fossils found thus far. Every find
leads us to reconceptualize possible lineages leading to humans. The following list includes
most of these fossils by their estimated date as well as primate precursors to the hominid line.
50 million years ago - the lemur
Flat face, short snout, large eyes set wide apart. Selection against sense of
smell for sense of vision, possibly because early primates were tree dwellers
(stereoscopic vision).
Next 20 million years sees the branching off of the present day monkey line from that of
the great apes and man.
30 million years ago - Aegyptopithecus
Found in the Fayum, in Egypt. Shorter snout than the lemur, teeth are
ape-like, larger but still lives in trees, spending part of the time on the
ground.
20 million years ago - Proconsul and Dryopithecus.
Brain markedly larger, eyes now fully forward in stereoscopic vision. Could be
on a branch line moving toward apes, not man. Teeth demonstrate that he is an
ape, since the jaw is locked by the big canines.
14 million years ago - Ramapithecus
Found in Kenya and India, indicating movement and dispersal. Jaw fragments
only showing teeth that are level and more human. Great canines are gone,
face much flatter. Man or ape?
Gap of 5 to 10 million years - hiding the time when the ape and human lines separated.
Now we have begun to find interesting fossils from this period, but it is still too difficult to
draw conclusions
Human - Chimp/Gorilla Separation
6-8 million years ago
7 million years ago - Sahelanthropus tchadensis (Toumaí)
Found in Chad, some 2,500 miles from the normal sites in East Africa,
suggesting a new site of origin for humanity. Not clear whether this was an ape
or human, or really the common ancestor of both. Brow ridges, teeth that look
like on a line to humans (larger molars and smaller cannines). No evidence
regarding upright posture.
The next two are recent finds that are controversial. Ape or human?
6 million years ago – Orrorin tugenensis (Kenya)
Appears to have walked upright (long femur neck), arms and fingers
retain adaptations for climbing, sharp canine teeth.
5.2-5.8 million years ago – Ardipithecus ramidus kadabba
Considered to be a subspecies of ardipithecus ramidus. We have found a
toe, teeth, an adult mandible, pieces of a skull, several arm bones, lowerjaw of a child. Could be chimpanzee. May have walked upright.
5 million years ago
Ardipithecus ramidus
(Ethiopia)
4.4 million years ago
Australopithecus anamensis
(Kenya)
4.2-3.9 million years ago
Australopithecus afarensis
(Lucy - Ethiopia)
3.0-3.9 million years
Two branches now appear (speciation). The second, Genus homo, appears somewhat
later than the first, the Australopithecines (“Southern Ape from Afar”):
1.
Genus Australopithecines - two forms: one lighter, and one a more robust
form. Erect but small-brained. [ Modern feet ]
The lighter "gracile" forms, composed of 3-5 species
Australopithecus africanus (Raymond Dart, 1920's)
3.0-2.3 million years ago.
In the Taung baby found by Raymond Dart, foramen
magnum is under skull indicating upright posture.
Teeth are small and square - indicates an animal
foraging with hands, not its mouth. Teeth may also
show it was eating raw meat. To get raw meat the
animal was probably making tools, pebble-tools, stone
choppers, to carve it and hunt.
Australopithecus aethiopicus – 2.6 million years ago.
Australopithecus garhi – 2.5 million years ago. Found with
earliest stone tools.
The heavier, more robust forms, which are sometimes placed in a different
genus called Paranthropus.
Australopithecus robustus (S. Africa) – 2.0-1.0 million years
ago. Generally nuts and tubors, but perhaps eating some meat.
Australopithecus boisei (Leakey, East Africa) – 2.3-1.2 million
years ago.
The Australopithecines lived and died entirely in Africa, with 1 or 2
species surviving until perhaps 1 million years ago.
2.
Genus Homo
Homo habilis (Leakey, Olduvai Gorge, Tanzania) 1.9-1.8 million years
ago.
Homo rudolfensis - a possible variation of homo habilis.
Homo erectus - 1.8 million – 300,000 years ago. The earliest fossil, of
"Turkana boy" (Leakey, 1985), is 1.6 million years.
Large brain size - 1,100 c.c. (three quarters of modern human
capacity), showing increase in species over time. Upright posture (as
early as 3.5 million years ago)
Populations of this species left Africa for Europe, China (Peking
Man) and Indonesia (Java Man). Earliest fossil in Indonesia is
1.8 or 1.9 million years old, leading to the idea that humans
originated in Indonesia. Appears to be an older line than
previously thought (less archeological work has been carried
out in south-east Asia than in Africa). The oldest known African
Homo erectus is 1.8 million years old - perhaps Homo erectus
is more than 2 million years old?
One million years ago Homo erectus lived on the 3 continents of Africa
(homo ergaster), Europe (homo antecessor) and Asia (home erectus).
Spread out of Africa
730,000 b.p. - first signs of humans in Europe
Homo heidelbergensis – 600,000 – 100,000 years ago. Generalized
diet, lived in Africa, Asia, and Europe.
Homo sapiens - 100 thousand years ago
Then between 500,000 and 100,000 years ago we begin finding a highly
confusing group of specimens called "archaic Homo sapiens" who lived on all 3
continents, presumably descendants of Homo erectus. In morphology seem to
be intermediate between Homo erectus and modern humans. It would seem
that Neanderthal is a direct descendent of these archaic Homo sapiens in
Europe.
500,000 b.p. evidence that fire was being used.
400,000 b.p. wooden spears
350,000 b.p. most areas of Europe settled.
The debate over Neanderthal Man. Discovered first in 1856 and has been found all over
Europe. Lived from 270,000 to 30,000 years ago. Was Neanderthal our direct ancestor or a
separate dead-end line competitively replaced by our true ancestors?
Two theories have arisen to explain what happened - the "multiregional view" and the
"out of Africa" view.
Multi-regionalist view (Franz Weidenreich - 1940's)
Homo erectus populations on all three continents evolved in parallel some migration provided gene flow and prevented all three from
differentiating into different species. Changes primarily involved
increased brain size and decreased jaws and teeth. Neanderthal
therefore represents the European version of a late stage in the global
trend.
Out of Africa view
Modern humans arose out of one isolated group of Homo erectus in
Africa, and then spread. The evidence for this view consists of:
The best and oldest remains of fully modern humans are from
100,000 to 125,000 year ago in Africa.
Genetic variability among modern Africans is larger than all
other humans, indicating long presence of modern humans
there.
Neanderthal therefore represents one among several non-African
descendents of Homo erectus that did not transform to modern
humans, but died out.
Homo sapiens sapiens - 50 thousand years ago
40-30,000 b.p. - By 30,000 years ago fully modern human types were
widespread through out the world. The earliest humans appear
to have inhabited a variety of habitats within a belt of tropical
and semi-tropical country stretching from Ethiopia to southern
Africa. The population was small, thinly spread, living in groups
which probably depended mainly on the gathering of nuts,
seeds and plants, which they would have supplemented by
scavenging dead animals killed by other predators and perhaps
the hunting of a few small mammals. This form of subsistence gathering and hunting - lasted as the human way of life until the
development of agriculture about 10,000 years ago.
During this period we see an expansion in the types of tools
being used from a previous 6 to over 80 types. Large hand
axes, which required minimum time and effort in production are
replaced by very thin, parallel-sided blades from the core of the
stone. 20,000 b.p. small projectile points being made. Bone,
antler and ivory tools.
New tools - required more complicated manufacturing
techniques such as heat treatment and pressure flaking from
core of stone. This implies higher motor abilities and greater
mental skills that could handle a several stage fabrication
process.
Humans in Nature: Hunter-Gatherers
Some 90% of all humans that ever lived have been hunter-gatherers, only 6%
agriculturalists, and a small % industrialists.
Gathering nuts, seeds, plants and supplementing this with scavenging dead
animals and perhaps hunting a few small mammals. Living in small groups, low
population and thinly spread.
Today's hunter-gatherers have been pushed into marginal areas - the Bushmen of
south Africa, the Hadza of east Africa, pygmies in equatorial forests of Africa, a
few groups in India and east Asia, some Aborigines in Australia, Inuit in the
Arctic and native inhabitants in tropical forests of South America.
We now believe that this life-style was relatively easy - gathering requires few
hours a day, with plenty of leisure time. Very few tools and instruments, which
would be hard to carry with their mobile life. Pattern of life varies throughout the
year depending on seasonal availability of foods. Hunting is a periodic activity,
lasting intensively for a week and then not at all for 2 or 3. Hunting is difficult,
hazardous and has only intermittent rewards. Very low rate of success. Easier to
scavenge for dead food when spears are poor.
Near the equator hunting is less frequent than in cooler climates where plants are
not as available.
Apparently hunter-gatherer groups have always had means of controlling their
population - infanticide, leaving the old to die, killing twins, the handicapped or
females.
Development of human societies and settlement across the globe was probably
due to 4 evolutionary changes that occurred during 2 million years:
1. Upright posture
2. Increase in brain size
3. Speech
4. Technology (making of tools)
2,000,000 b.p. stone tools - chopper made from pebbles and a
hand axe with a working edge round most of the
perimeter. Easy to make and found in large quantities.
500,000 b.p. evidence that fire was being used.
400,000 b.p. wooden spears
80,000 b.p. bolas stones for entangling animals
Delayed maturation of the nervous system, ability to handle fine detail,
control over state and ability to make plans for the future.
Settlement Across the Globe
Original home: from Ethiopia to South Africa
Move to frost-free zones of middle east, India, south China and parts of
Indonesia. Clothing would have been necessary in addition to tools.
Homo erectus had spread out of Africa by 1 and a half million years ago.
Hunter-Gatherer Effects on Environment
Possibly caused animal extinctions, plant extinctions.
Should be considered "affluent societies" - rich variety of foods, less
disease, more leisure time.
History of Agriculture
The way we make a living has changed during our evolution – from hunter-gatherer
groups, to herding nomads, to agriculture
Agriculture developed separately over the course of a few thousand years in south-west
Asia, China and Mesoamerica. The most important transition in human history. Capable
of providing larger quantities of food and therefore settled communities. Once started it
couldn't be stopped, because the increase in population it created couldn't be supported
by the old methods of hunting and gathering.
Bronowski (The Ascent of Man) calls the agricultural revolution a “biological
revolution” because it involved not only the cultivation of plants but also the
domestication of animals. These in turn led to a social revolution.
The transition represents a shift in the spectrum of activities engaged in by "hunters and
gatherers". They did practice certain forms of cultivation. The move has been from
foraging of wild plants, tending wild plants through cultivation, domestication of
genetically distinct crops some of which can only propagate through human
intervention, (breeding), and finally genetically engineered plants.
Cultivation of animals goes through a similar sequence: random hunting of a herd,
controlled predation, heard following, loose herding, close herding and finally modern
intensive factory farming.
Neither of these required the development of radically different techniques from what
they were doing before.
Why adopt agriculture? It was probably necessary because of population pressure. The
population of 4 million (10,000 years ago) was probably the maximum size possible
given the hunting and gathering way of life. As movement became less possible, groups
were forced into less favourable areas for subsistence, and eventually would have been
forced to exploit what were seen at the time as less favourable resources.
In a nomadic life, there was no room for innovation. If you had to pack up and move on
frequently, you could not carry a lot of extras with you. Culture therefore could not take
off in a big way.
Domestication of both plants and animals.
Dogs probably first. Sheep and goats (which have no natural migratory patterns to
follow) about 10,000 years ago. Draught animals – ox, onager, ass, the horse
(about 2000 b.c.)
In the nomadic life, everything has to be carried. No time for skill or
specialization. No room for innovation.
Every stage in the domestication of plants and animals requires new inventions.
The sickle – flint set in gazelle horn or bone – flat edge. A serrated edge is
necessary for cutting wheat.
The plough – a lever – a wedge to divide the soil.
The wheel – 3000 B.C. in the southern Russian steppes – grinding wheat, the
cart, the pulley, the bow lathe.
The plough and the wheel were not invented in the Americas because both needed
draught animals, and there were none. Planting was done with a digging stick and pack
for carrying seeds.
Humans against Nature: Agricultural Societies
(Handouts: "Noble Savages" and "The Worst Mistake in the History of the Human
Race"
Has human history over the past million years been a long tale of progress?
Archeologists are discovering that the adoptation of agriculture was in many ways a
catastrophe from which we never recovered. With agriculture came the gross social
and sexual inequality, disease and despotism, that curse our existence.
10,000 -12,000 years ago became food producers via domestication of animals
and cultivators of plants.
Horticulture - growing plants close to home.
Slash-and-burn or swidden - cutting forest for planting crops, ash works as
fertilizer, a variety of roots, tubers, and seeds and tree-crops planted.
Development of a food surplus had 6 major consequences:
1. Population increase.
2. Landscape slowly changes from forest to open habitats.
Desertification. Irrigation without proper drainage.
3. Urbanization around fields.
4. Health decline.
5. Social classes. Land and water rights. Encourages open conflict.
Concentration of power in few. Much individual freedom given up
for group living.
6. Encouraged inequality between sexes.
Humans against Nature: Industrial Societies
Initiated by change from animal, wind, water power to fossil fuels - coal, oil,
gas. Makes large scale mining possible.
Introduces various types of pollution and work monotony.
Humans and Nature: A Sustainable-Earth Society