Human evolution by martin

HUMAN EVOLUTION
By
M.N.O. UWAMOSE
DEPARTMENT OF ANIMAL AND ENVIRONMENTAL BIOLOGY,
FACULTY OF SCIENCE,
DELTA STATE UNIVERSITY, ABRAKA.
February, 2014

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TABLE OF CONTENT
1.0 Introduction
2.0 Evolutionary Theory
3.0 Process of Evolution
4.0 History of Human Evolution
5.0 Paleoanthropology
6.0 Evidence of Evolution
6.1 Evidence from comparative physiology
6.2 Evidence from comparative anatomy
6.3 Evidence from comparative embryology
6.4 Evidence from comparative morphology
6.5 Evidence from vestigial organs
6.6 Genetics
6.7 Evidence from Molecular Biology
6.8 Evidence from the Fossil Record
7.0 Divergence of the Human Clade from other Great Apes
8.0 Anatomical changes
8.1 Anatomy of bipedalism
8.2 Encephalization
8.3 Sexual dimorphism
8.4 Other changes
9.0 Genus Homo
10.0 Homo Sapiens Taxonomy
11.0 Conclusion
12.0 References

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1.0 INTRODUCTION
Evolution is the genetic transformation of populations over time. In this sense,
a population is a group of living things which randomly mate with one another.
A species on the other hand is a group of populations whose members can
interbreed. If two populations of a species are separated and grown genetically
apart they won't be able to produce fertile offspring together anymore. It is at
this point where they become different species.
Human evolution is the evolutionary process leading up to the appearance of
modern humans. It is the process by which human beings developed on Earth
from now-extinct primates. It involves the lengthy process of change by which
people originated from apelike ancestors. The study of human evolution
involves many scientific disciplines, including physical anthropology,
primatology, archaeology, ethology, evolutionary psychology, embryology and
genetics. Scientific evidence shows that the physical and behavioural traits
shared by all people originated from apelike ancestors and evolved over a
period of approximately six million years.
2.0 EVOLUTIONARY THEORY
Before evolutionary theory was developed, the general consensus in the world
was based on religious doctrine, which was that species did not change from

generations to generations. Some churches still maintains that there was a
special and independent creation of species they known as Creationism which
was from the Judeo-Christian bible. During the Renaissance however,
scientists started looking at nature in a more open-minded way. Over time they
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collected evidence that species did in fact change over time.
The possibility of linking humans with earlier apes by descent became clear
only after 1859 with the publication of Charles Darwin's On the Origin of
Species, in which he argued for the idea of the evolution of new species from
earlier ones. Darwin's book did not address the question of human evolution,
saying only that "Light will be thrown on the origin of man and his history".
It was Charles Darwin (1809-82) however who developed the theory of natural
selection which is still supported today. He was able to observe and notice
while doing field research work that members of a population had different
traits among them. Thinking of about this, he realized that these variations in
trait must be more useful for survival than others. He also realized that the
individuals with the most favorable trait based on the environment, was more
likely to survive and pass on the favorable trait to their offspring, thereby
increasing its prevalence in the population.
The first debates about the nature of human evolution arose between Thomas
Huxley and Richard Owen. Huxley argued for human evolution from apes by

illustrating many of the similarities and differences between humans and apes,
and did so particularly in his 1863 book Evidence as to Man's Place in Nature.
However, many of Darwin's early supporters (such as Alfred Russell Wallace
and Charles Lyell) did not initially agree that the origin of the mental capacities
and the moral sensibilities of humans could be explained by natural selection,
though this later changed. Darwin applied the theory of evolution and sexual
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selection to humans when he published The Descent of Man in 1871.
3.0 PROCESS OF EVOLUTION
The process of evolution involves a series of natural changes that cause species
(populations of different organisms) to arise, adapt to the environment, and
become extinct. All species or organisms have originated through the process
of biological evolution. In animals that reproduce sexually, including humans,
the term species refers to a group whose adult members regularly interbreed,
resulting in fertile offspring i.e., offspring themselves are capable of
reproducing. Scientists classify each species with a unique, two-part scientific
name. In this system, modern humans are classified as Homo sapiens.
Evolution occurs when there is change in the genetic material the chemical
molecule, DNA which is inherited from the parents, and especially in the
proportions of different genes in a population. Genes represent the segments of
DNA that provide the chemical code for producing proteins. Information

contained in the DNA can change by a process known as mutation. The way
particular genes are expressed i.e., how they influence the body or behaviour of
an organism can also change. Genes affect how the body and behaviour of an
organism develop during its life, and this is why genetically inherited
characteristics can influence the likelihood of an organism’s survival and
reproduction.
Evolution does not change any single individual. Instead, it changes the
inherited means of growth and development that typify a population. Parents
pass adaptive genetic changes to their offspring, and ultimately these changes
become common throughout a population. As a result, the offspring inherit
those genetic characteristics that enhance their chances of survival and ability
to give birth, which may work well until the environment changes. Over time,
genetic change can alter a species' overall way of life, such as what it eats, how
it grows, and where it can live. Human evolution took place as new genetic
variations in early ancestor populations favoured new abilities to adapt to
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environmental change and so altered the human way of life.
4.0 HISTORY OF HUMAN EVOLUTION
The first members of the human family, Hominidae, first evolved in Africa,
and much of human evolution occurred on that continent. The fossils of early
humans who lived between 4 and 6 million years ago come entirely from

Africa. They spent much of their time in trees, as their close primate relatives
did, who are the ancestors of today's chimpanzees and gorillas. But unlike
other primates, the early hominids walked readily on two legs when on the
ground (Bipedalism), one of the earliest traits often used to define the human
family. Anthropologists and evolutionary biologists agree that upright posture
and the subsequent ability to walk on two legs was a crucial major adaptation
associated with the divergence of the human lineage from a common ancestor
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with the African apes.
Other important human characteristics such as a large and complex brain, the
ability to make and use tools, and the capacity for language developed more
recently. Many advanced traits including complex symbolic expression, art,
and elaborate cultural diversity emerged mainly during the past 100,000 years.
Between the time of the first hominids and the period when our species, Homo
sapiens, evolved in Africa, our planet was home to a wide range of early
humans. Physical and genetic similarities show that the modern human species,
Homo sapiens, has a very close relationship to another group of primate
species, the apes. Humans and the great apes (large apes) of Africa, the
chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and
gorillas share a common ancestor that lived between 6 and 8 million years ago.

Scientists over the years are able to understand the story through wealth of
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evidence including fossils, artefacts and DNA analysis.
Most scientists currently recognize some 15 to 20 different species of early
humans. Scientists do not all agree, however, about how these species are
related or which ones simply died out. Many early human species certainly the
majority of them left no living descendants. Scientists also debate over how to
identify and classify particular species of early humans, and about what factors
influenced the evolution and extinction of each species.
Early humans first migrated out of Africa into Asia probably between 2 million
and 1.8 million years ago. They entered Europe somewhat later, between 1.5
million and 1 million years. Species of modern humans populated many parts
of the world much later. For instance, people first came to Australia probably
within the past 60,000 years and to the Americas within the past 30,000 years
or so. The beginnings of agriculture and the rise of the first civilizations
occurred within the past 12,000 years.
5.0 PALEOANTHROPOLOGY
Paleoanthropology is the scientific study of human evolution.
Paleoanthropology is a subfield of anthropology, the study of human culture,
society, and biology. The field involves an understanding of the similarities

and differences between humans and other species in their genes, body form,
physiology, and behaviour. Paleoanthropologists search for the roots of human
physical traits and behaviour. They seek to discover how evolution has shaped
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the potentials, tendencies, and limitations of all people.
Paleoanthropology is an exciting scientific field because it investigates the
origin, over millions of years, of the universal and defining traits of our
species. However, some people find the concept of human evolution troubling
because it can seem not to fit with religious and other traditional beliefs about
how people, other living things, and the world came to be. Nevertheless, many
people have come to reconcile their beliefs with the scientific evidence. Early
human fossils and archaeological remains offer the most important clues about
this ancient past. These remains include bones, tools and any other evidence
(such as footprints, evidence of hearths, or butchery marks on animal bones)
left by earlier people. Usually, the remains were buried and preserved
naturally. They are then found either on the surface (exposed by rain, rivers,
and wind erosion) or by digging in the ground. By studying fossilized bones,
scientists learn about the physical appearance of earlier humans and how it
changed. Bone size, shape, and markings left by muscles tell us how those
predecessors moved around, held tools, and how the size of their brains
changed over a long time.

During the 1960s and 1970s, hundreds of fossils were found, particularly in
East Africa in the regions of the Olduvai Gorge and Lake Turkana. The driving
force in the East African researches was the Leakey family, with Louis Leakey
and his wife Mary Leakey, and later their son Richard and daughter in-law
Meave being among the most successful fossil hunters and
paleoanthropologists. From the fossil beds of Olduvai and Lake Turkana they
amassed fossils of australopithecines, early Homo and even Homo erectus.
These finds cemented Africa as the cradle of humankind. In the 1980s,
Ethiopia emerged as the new hot spot of palaeoanthropology as "Lucy", the
most complete fossil member of the species Australopithecus afarensis, was
found by Donald Johanson in Hadar in the desertic Middle Awash region of
northern Ethiopia. This area would be the location of many new hominin
fossils, particularly those uncovered by the teams of Tim White in the 1990s,
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such as Ardipithecus ramidus.
6.0 EVIDENCE OF EVOLUTION
According to Charles Darwin, (The Descent of Man and Selection in Relation
to Sex, 2nd edition) he who wishes to decide whether man is the modified
descendant of some pre-existing form, would probably first enquire whether
man varies, however slightly, in bodily structure and in mental faculties; and if

so, whether the variations are transmitted to his offspring in accordance with
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the laws which prevail with the lower animals.
The evidence on which scientific accounts of human evolution is based comes
from many fields of natural science. The main sources of knowledge about the
evolutionary process has traditionally been the fossil record, but since the
development of genetics beginning in the 1970s, DNA analysis has come to
occupy a place of comparable importance. The studies of ontogeny, phylogeny
and especially evolutionary developmental biology of both vertebrates and
invertebrates offer considerable insight into the evolution of all life, including
how humans evolved.
6.1 Evidence from comparative physiology
Many basic similarities in physiologic and chemical properties parallel the
morphologic features of organisms.
Many individual digestive enzymes present in different animals are essentially
alike in physiologic action. Trypsin, which acts upon proteins, occurs in many
animals right from protozoans to man, an amylase, which acts on starches, is
present from sponges to mammals.
Some hormones derived from endocrine glands show like reactions when
injected into different animals. The thyroid gland present in all vertebrates has

been proved to be exchangeable among them. For example, the thyroid gland
in cattle controls their rate of metabolism; extracts of this gland has been
successfully used to feed human beings deficient in their own thyroid secretion
to speed up bodily metabolism. If beef or sheep thyroid is fed to frog tadpoles
from which the thyroid gland has been removed, the tadpoles will grow
normally and later metamorphose into frogs. This proves that all vertebrates
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descended from a common ancestor.
6.2 Evidence from comparative embryology
Every multicellular animal originates from zygote or fertilized egg, except for a
few specialized types of reproduction. The eggs of each species have a
distinctive ability to produce an individual of that species, but there are many
features of embryonic development common to members of any anima group.
Fertilized eggs segment, pass through a blastula stage and a two-layered
gastrula stage, then become variously differentiated.
A study of the development of embryo of vertebrate groups by Von Baer
(1792-1876) revealed striking similarities occurring in all the groups
particularly during cleavage, gastulation and the early stages of differentiation.
Haeckel suggested that this had an evolutionary significance. He formulated
the principle of Biogenesis which states that ontogeny recapitulates phylogeny
that is during the development of an individual, it passes through many

embryonic stages that its ancestor underwent because the mechanism of
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development was inherited from a common ancestor.
In the development of human embryo, many primitive features appear and
disappear. The appearance of gill slits like those of fish, two chambered heart
like those of amphibians, possession of tail like those of reptiles and coat of
hair like those of monkeys, indicates that humans evolved through the fish,
amphibians, reptile and mammalian line.
The beginning embryo in a hen’s egg, has at first the vertebrate essentials of a
notochord, dorsal nervous system, and somites; later, it acquires bird features
such as beak and wings; and, much later, there appear the characteristics of a
chicken instead of a pigeon or duck.
The whalebone whales have no teeth in the adult stage but their embryos have
tooth buds which are absorbed as development continues. Birds have no teeth
but their embryos have teeth buds. Thus the presence of the teeth buds in
whales and birds proves that they have descended from ancestors that had
teeth.

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Figure 1. Different stages in the development of three vertebrate animals.
Note their similarities in the very early stages and their differences in their stages.

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6.3 Evidence from comparative anatomy
The comparative study of the anatomy of groups reveals that certain structural
features are basically similar. In examining animals for structural evidences of
evolution it is necessary to distinguish characters that are of common origin
(homology), hence indicative of common ancestry in descent, from purely
adaptive features that are of similar function (analogy) but of unlike origin.
Homologous structures can be used to explain the evidence of comparative
anatomy. Homologous structures are structure built in the same body plan but
modified to perform different functions. The forelimbs of frogs, whales, horse,
bird and man are in the pentadactyl plan but this basic structure have been
modified to perform different functions. Thus, the forelimb of frog is modified
for landing, that of bird modified as wing for flying, the horse forlimb has only
one finger for fast running, that of whale is used for swimming while in man,
the forelimb could be rotated and has five fingers for holding and grasping.
These different functions are brought about due to differences in the
environment. It can be explained therefore that the pentadactyl plan of the
forelimb of vertebrates indicate a genetic relationship and common ancestor.

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Figure 2. The pentadactyl plan of forelimb of vertebrates.
6.4 Evidence from vestigial organs
Vestigial organ is another convincing aspect of comparative anatomy. Vestigial
organs are homologous structures in some species that have no apparent
function, they are rudimentary or useless organs and of reduced size. From the
standpoint of special creation these are difficult to explain but from that of
evolution they are obviously features that were functional and necessary in
their ancestors but are now in process of disappearance from living organisms.
In man, the appendix is a slender vestige about 2 ½ in. long that seems to have

little function and often is a site of infection requiring its surgical removal.
Although this organ is not concerned with digestion, is homologous with the
functional appendix of herbivorous mammals such as cow and goat. Another
example is the nonfunctional bones of snake and whale which are thought to be
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homologous with the hip bones and hindlimbs of quadruped vertebrates.
Figure 3. Vestigial organ of man.

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6.5 Genetics
Human evolutionary genetics studies how one human genome differs from the
other, the evolutionary past that gave rise to it, and its current effects.
Differences between genomes have anthropological, medical and forensic
implications and applications. Genetic data can provide important insight into
human evolution.
6.6 Evidence from Molecular Biology
This indicates the molecular basis of life that has evolved early and has been
maintained with little variation across all life on the continent. The closest
living relatives of humans are bonobos and chimpanzees (both genus Pan) and
gorillas (genus Gorilla). With the sequencing of both the human and
chimpanzee genome, current estimates of the similarity between their DNA
sequences range between 95% and 99%. By using the technique called the
molecular clock which estimates the time required for the number of divergent
mutations to accumulate between two lineages, the approximate date for the
split between lineages can be calculated. The gibbons (family Hylobatidae) and
orangutans (genus Pongo) were the first groups to split from the line leading to
the humans, then gorillas followed by the chimpanzees and bonobos. The
splitting date between human and chimpanzee lineages is placed around 4-8
million years ago during the late Miocene epoch.

Genetic evidence has also been employed to resolve the question of whether
there was any gene flow between early modern humans and Neanderthals, and
to enhance our understanding of the early human migration patterns and
splitting dates. By comparing the parts of the genome that are not under natural
selection and which therefore accumulate mutations at a fairly steady rate, it is
possible to reconstruct a genetic tree incorporating the entire human species
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since the last shared ancestor.
Each time a certain mutation (Single nucleotide polymorphism) appears in an
individual and is passed on to his or her descendant a haplogroup is formed
including all of the descendants of the individual who will also carry that
mutation. By comparing mitochondrial DNA which is inherited only from the
mother, geneticists have concluded that the last female common ancestor
whose genetic marker is found in all modern humans, the so-called
mitochondrial Eve, must have lived around 200,000 years ago.
6.7 Evidence from the Fossil Record
Fossils serve to highlight the differences and similarities between the current
and extinct species showing the evolution of form over time. There is little
fossil evidence for the divergence of the gorilla, chimpanzee and hominin
lineages. The earliest fossils that have been proposed as members of the
hominin lineage are Sahelanthropus tchadensis dating from 7 million years

ago, Orrorin tugenensis dating from 5.7 million years ago and Ardipithecus
kadabba dating to 5.6 million years ago. Each of these has been argued to be a
bipedal ancestor of later hominins but, in each case, the claims have been
contested. It is also possible that one or more of these species are ancestors of
another branch of African apes, or that they represent a shared ancestor
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between hominins and other apes.
From these early species, the australopithecines arose around 4 million years
ago and diverged into robust (also called Paranthropus) and gracile branches,
one of which (possibly A. garhi) probably went on to become ancestors of the
genus Homo. The australopithecine species that is best represented in the fossil
record is Australopithecus afarensis with more than one hundred fossil
individuals represented, found from Northern Ethiopia (such as the famous
"Lucy"), to Kenya, and South Africa. Fossils of robust australopithecines such
as A. robustus (or alternatively Paranthropus robustus) and A. /P. boisei are
particularly abundant in South Africa at sites such as Kromdraai and
Swartkrans, and around Lake Turkana in Kenya.
The earliest members of the genus Homo are Homo habilis which evolved
around 2.3 million years ago. Homo habilis is the first species for which we
have positive evidence of the use of stone tools. They developed the oldowan
lithic technology, named after the Olduvai gorge in which the first specimens

were found. Some scientists consider Homo rudolfensis, a larger bodied group
of fossils with similar morphology to the original H. habilis fossils, to be a
separate species while others consider them to be part of H. habilis - simply
representing species internal variation, or perhaps even sexual dimorphism.
The brains of these early hominins were about the same size as that of a
chimpanzee, and their main adaptation was bipedalism as an adaptation to
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terrestrial living.
During the next million years, a process of encephalization began and, with the
arrival of Homo erectus in the fossil record, cranial capacity had doubled.
Homo erectus was the first of the hominina to leave Africa, and this species
spread through Africa, Asia, and Europe between 1.3 to 1.8 million years ago.
One population of H. erectus, also sometimes classified as a separate species
Homo ergaster, stayed in Africa and evolved into Homo sapiens. It is believed
that these species were the first to use fire and complex tools.
The earliest transitional fossils between H. ergaster/erectus and Archaic H.
sapiens are from Africa, such as Homo rhodesiensis, but seemingly transitional
forms were also found at Dmanisi, Georgia. These descendants of African H.
erectus spread through Eurasia from ca. 500,000 years ago evolving into H.
antecessor, H. heidelbergensis and H. neanderthalensis. The earliest fossils of
anatomically modern humans are from the Middle Paleolithic, about 200,000

years ago such as the Omo remains of Ethiopia; later fossils from Skhul in
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Israel and Southern Europe begin around 90,000 years ago.
As modern humans spread out from Africa, they encountered other hominins
such as Homo neanderthalensis and the so-called Denisovans, who may have
evolved from populations of Homo erectus that had left Africa around 2
million years ago. The nature of interaction between early humans and these
sister species has been a long standing source of controversy, the question
being whether humans replaced these earlier species or whether they were in
fact similar enough to interbreed, in which case these earlier populations may
have contributed genetic material to modern humans.
Figure 4a: Replica of fossil skull of Homo habilis. Figure 4b: Replica of fossil skull of Homo ergaster
Fossil number KNM ER 1813, (African Homo erectus ).
Found at Koobi Fora, Kenya. Fossil number KHM HEU 3733, discovered in
Kenya, 1975.

7.0 DIVERGENCE OF THE HUMAN CLADE FROM OTHER
GREAT APES
Species close to the last common ancestor of gorillas, chimpanzees and humans
may be represented by Nakalipithecus fossils found in Kenya and
Ouranopithecus found in Greece. Molecular evidence suggests that between 8
and 4 million years ago, first the gorillas, and then the chimpanzees (genus
Pan) split off from the line leading to the humans; human DNA is
approximately 98.4% identical to that of chimpanzees when comparing single
nucleotide polymorphisms. The fossil record of gorillas and chimpanzees is
limited. Both poor preservation (rain forest soils tend to be acidic and dissolve
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bone) and sampling bias probably contribute to this problem.
Other hominins likely adapted to the drier environments outside the equatorial
belt, along with antelopes, hyenas, dogs, pigs, elephants, and horses. The
equatorial belt contracted after about 8 million years ago. There is very little
fossil evidence for the split of the hominin lineage from the lineages of gorillas
and chimpanzees. The earliest fossils that have been argued to belong to the
human lineage are Sahelanthropus tchadensis (7 million years ago) and
Orrorin tugenensis (6 million years ago), followed by Ardipithecus (5.5–4.4
million years ago), with species Ar. kadabba and Ar. Ramidus.

Figure 5: Family tree showing the extant hominoids: humans (genus Homo), chimpanzees
and bonobos (genus Pan), gorillas (genus Gorilla), orangutans (genus Pongo), and gibbons
(four genera of the family Hylobatidae: Hylobates, Hoolock, Nomascus, and Symphalangus).
All except gibbons are hominids.
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8.0 ANATOMICAL CHANGES
Human evolution is characterized by a number of morphological,
developmental, physiological, and behavioral changes that have taken place
since the split between the last common ancestor of humans and chimpanzees.
The most significant of these adaptations are bipedalism, increased brain size,
lengthened ontogeny (gestation and infancy), and decreased sexual
dimorphism. The relationship between these changes is the subject of ongoing
debate. Other significant morphological changes included the evolution of a
power and precision grip, a change first occurring in H. erectus (Brues and
Snow 1965).
8.1 Anatomy of Bipedalism
Bipedalism is not unique to humans; it is the basic adaption of the Hominin line
and is considered the main cause behind a suite of skeletal changes shared by

all bipedal hominins. Homo sapiens is the only mammal that is adapted
exclusively to bipedal striding. Accordingly, human bipedalism is a natural
development from the basic arboreal primate body plan, in which the hind
limbs are used to move about and sitting upright is common during feeding and
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rest.
The initial changes toward an upright posture were probably related more to
standing, reaching, and squatting than to extended periods of walking and
running. Human beings stand with fully extended hip and knee joints, such that
the thighbones are aligned with their respective leg bones to form continuous
vertical columns (Lewin 1988). To walk, one simply tilts forward slightly and
then keeps up with the displaced centre of mass, which is located within the
pelvis. The large muscle masses of the human lower limbs power our
locomotion and enable a person to rise from squatting and sitting postures.
Body mass is transferred through the pelvis, thighs, and legs to the heels, balls
of the feet, and toes. Remarkably little muscular effort is expended to stand in
place. Indeed, our large buttock, anterior thigh, and calf muscles are virtually
unused when we stand still. Instead of muscular contraction, the human bipedal
stance depends more on the way in which joints are constructed and on
strategically located ligaments that hold the joints in position. Fortunately for
paleoanthropologists, some bones show dramatic signs of how a given hominin

carried itself and the adaptation to obligate terrestrial bipedalism led to notable
anatomic differences between hominins and great apes. These differences are
readily identified in fossils, particularly those of the pelvis and lower limbs.
Human feet are distinct from those of apes and monkeys. This is not surprising,
since in humans the feet must support and propel the entire body on their own
instead of sharing the load with the forelimbs. In humans the heel is very
robust, and the great toe is permanently aligned with the four diminutive lateral
toes. Unlike other primate feet, which have a mobile midfoot, the human foot
possesses (if not requires) a stable arch to give it strength. Accordingly, human
footprints are unique and are readily distinguished from those of other animals
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(Srivastava 2009).
Figure 6. The hominoids are descendants of a common ancestor

pg. 27
8.2 Encephalization
The human species developed a much larger brain than that of other primates –
typically 1,330 cm3 in modern humans, over twice the size of that of a
chimpanzee or gorilla. The pattern of encephalization started with Homo
habilis, which at approximately 600 cm3 had a brain slightly larger than that of
chimpanzees, and continued with Homo erectus (800–1,100 cm3), reaching a
maximum in Neanderthals with an average size of (1,200–1,900 cm3), larger
even than Homo sapiens. The pattern of human postnatal brain growth differs
from that of other apes (heterochrony) and allows for extended periods of
social learning and language acquisition in juvenile humans. However, the
differences between the structure of human brains and those of other apes may
be even more significant than differences in size. The increase in volume over
time has affected areas within the brain unequally – the temporal lobes, which
contain centers for language processing, have increased disproportionately, as
has the prefrontal cortex which has been related to complex decision-making
and moderating social behavior. Encephalization has been tied to an increasing
emphasis on meat in the diet, or with the development of cooking, and it has
been proposed that intelligence increased as a response to an increased
necessity for solving social problems as human society became more complex.

Figure 7. Craniums – 1. Gorilla, 2. Australopithecus, 3. Homo erectus, 4. Neanderthal, 5.
Steinheim Skull, 6. Euhominid.
8.3 Sexual Dimorphism
The reduced degree of sexual dimorphism is visible primarily in the reduction
of the male canine tooth relative to other ape species (except gibbons) and
reduced brow ridges and general robustness of males. Another important
physiological change related to sexuality in humans was the evolution of
hidden estrus. Humans and bonobos are the only apes in which the female is
fertile year round and in which no special signals of fertility are produced by
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the body (such as genital swelling during estrus).
Nonetheless, humans retain a degree of sexual dimorphism in the distribution
of body hair and subcutaneous fat, and in the overall size, males being around

15% larger than females. These changes taken together have been interpreted
as a result of an increased emphasis on pair bonding as a possible solution to
the requirement for increased parental investment due to the prolonged infancy
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of offspring.
Other Changes
A number of other changes have also characterized the evolution of humans,
among them an increased importance on vision rather than smell; a smaller gut;
loss of body hair; evolution of sweat glands; a change in the shape of the dental
arcade from being u-shaped to being parabolic; development of a chin (found
in Homo sapiens alone), development of styloid processes; development of a
descended larynx.
9.0 GENUS HOMO
The word homo, the name of the biological genus to which humans belong, is
Latin for "human". It was chosen originally by Carolus Linnaeus in his
classification system. The word "human" is from the Latin humanus, the
adjectival form of homo. Linnaeus and other scientists of his time also
considered the great apes to be the closest relatives of humans based on
morphological and anatomical similarities.

Homo sapiens is the only old and still existing species of its genus, Homo.
While some other, extinct Homo species might have been ancestors of Homo
sapiens, many were likely our "cousins", having separated away from our
ancestral line (Strait et al. 1997). There is not yet a consensus as to which of
these groups should count as separate species and which as subspecies. In some
cases this is due to the dearth of fossils, in other cases it is due to the slight
differences used to classify species in the Homo genus (Bill 2004). The Sahara
pump theory (describing an occasionally passable "wet" Sahara Desert)
provides one possible explanation of the early variation in the genus Homo.
Based on archaeological and paleontological evidence, it has been possible to
infer, to some extent, the ancient dietary practices of various Homo species and
to study the role of diet in physical and behavioral evolution within Homo.
pg. 30
H. habilis and H. gautengensis
Homo habilis lived from about 2.4 to 1.4 million years ago. Homo habilis
evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5–
2 million years ago, when it diverged from the australopithecines. Homo
habilis had smaller molars and larger brains than the australopithecines, and
made tools from stone and perhaps animal bones. One of the first known
hominids, it was nicknamed 'handy man' by discoverer Louis Leakey due to
its association with stone tools. Some scientists have proposed moving this

species out of Homo and into Australopithecus due to the morphology of its
skeleton being more adapted to living on trees rather than to moving on two
pg. 31
legs like Homo sapiens (Wood and Collard 1999).
It was considered to be the first species of the genus Homo until May 2010,
when a new species, Homo gautengensis was discovered in South Africa that
most likely arose earlier than Homo habilis.
Figure 8. A reconstruction of Homo habilis
H. rudolfensis and H. georgicus
These are proposed species names for fossils from about 1.9–1.6 million years
ago, whose relation to Homo habilis is not yet clear.
 Homo rudolfensis refers to a single, incomplete skull from Kenya.
Scientists have suggested that this was another Homo habilis, but this
has not been confirmed.

 Homo georgicus, from Georgia, may be an intermediate form between
pg. 32
Homo habilis and Homo erectus, or a sub-species of Homo erectus.
H. ergaster and H. erectus
The first fossils of Homo erectus were discovered by Dutch physician Eugene
Dubois in 1891 on the Indonesian island of Java. He originally named the
material Pithecanthropus erectus based on its morphology, which he
considered to be intermediate between that of humans and apes. Homo erectus
(H. erectus) lived from about 1.8 million years ago to about 70,000 years ago
(which would indicate that they were probably wiped out by the Toba
catastrophe; however, Homo erectus soloensis and Homo floresiensis survived
it). Often the early phase, from 1.8 to 1.25 million years ago, is considered to
be a separate species, Homo ergaster, or it is seen as a subspecies of Homo
erectus, Homo erectus ergaster.
In the early Pleistocene, 1.5–1million years ago, in Africa some populations of
Homo habilis are thought to have evolved larger brains and made more
elaborate stone tools; these differences and others are sufficient for
anthropologists to classify them as a new species, Homo erectus (Spoor et al.
1994). This was made possible by the evolution of locking knees and a

different location of the foramen magnum (the hole in the skull where the spine
pg. 33
enters). They may have used fire to cook their meat.
A famous example of Homo erectus is Peking Man; others were found in Asia
(notably in Indonesia), Africa, and Europe. Many paleoanthropologists now
use the term Homo ergaster for the non-Asian forms of this group, and reserve
Homo erectus only for those fossils that are found in Asia and meet certain
skeletal and dental requirements which differ slightly from H. ergaster.
H. cepranensis and H. antecessor
These are proposed as species that may be intermediate between H. erectus and
H. heidelbergensis.
 H. antecessor is known from fossils from Spain and England that are
dated 1.2 million years ago–500 thousand years ago.
 H. cepranensis refers to a single skull cap from Italy, estimated to be
about 800,000 years old.
H. heidelbergensis
H. heidelbergensis (Heidelberg Man) lived from about 800,000 to about
300,000 years ago. Also proposed as Homo sapiens heidelbergensis or Homo
sapiens paleohungaricus.

pg. 34
Figure 9: Reconstruction of Homo heidelbergensis
The direct ancestor of both Homo neanderthalensis and Homo sapiens
H. rhodesiensis, and the Gawis cranium
 H. rhodesiensis, estimated to be 300,000–125,000 years old. Most
current researchers place Rhodesian Man within the group of Homo
heidelbergensis, though other designations such as Archaic Homo
sapiens and Homo sapiens rhodesiensis have been proposed.
 In February 2006 a fossil, the Gawis cranium, was found which might
possibly be a species intermediate between H. erectus and H. sapiens or
one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is
believed to be 500,000–250,000 years old. Only summary details are
known, and the finders have not yet released a peer-reviewed study.
Gawis man's facial features suggest its being either an intermediate
species or an example of a "Bodo man" female.
Neanderthal and Denisova hominin

Harvati (2003) alternatively designated H. neanderthalensis as Homo sapiens
neanderthalensis. They lived in Europe and Asia from 400,000 to about 30,000
years ago (Herrera, et al. 2009). Evidence from sequencing mitochondrial
DNA indicated that no significant gene flow occurred between H.
neanderthalensis and H. sapiens, and, therefore, the two were separate species
that shared a common ancestor about 660,000 years ago (Krings et al. 1997).
However, the 2010 sequencing of the Neanderthal genome indicated that
Neanderthals did indeed interbreed with anatomically modern humans circa
45,000 to 80,000 years ago (at the approximate time that modern humans
migrated out from Africa, but before they dispersed into Europe, Asia and
pg. 35
elsewhere).
Nearly all modern non-African humans have 1% to 4% of their DNA derived
from Neanderthal DNA, and this finding is consistent with recent studies
indicating that the divergence of some human alleles dates to one million years
ago, although the interpretation of these studies has been questioned
(Hebsgaard et al. 2007). Competition from Homo sapiens probably contributed
to Neanderthal extinction. They could have co-existed in Europe for as long as
10,000 years, during which human populations exploded vastly outnumbering
Neanderthals, possibly outcompeting them by sheer numerical strength
(Mellars et al. 2011).

In 2008, archaeologists working at the site of Denisova Cave in the Altai
Mountains of Siberia uncovered a small bone fragment from the fifth finger of
a juvenile member of a population now referred to as Denisova hominins, or
simply Denisovans (Brown 2010). Artifacts, including a bracelet, excavated in
the cave at the same level were carbon dated to around 40,000 BP. As DNA
had survived in the fossil fragment due to the cool climate of the Denisova
pg. 36
Cave, both mtDNA and nuclear genomic DNA were sequenced.
While the divergence point of the mtDNA was unexpectedly deep in time, the
full genomic sequence suggested the Denisovans belonged to the same lineage
as Neanderthals, with the two diverging shortly after their line split from that
lineage giving rise to modern humans (Reich et al. 2010). Modern humans are
known to have overlapped with Neanderthals in Europe for more than 10,000
years, and the discovery raises the possibility that Neanderthals, modern
humans and the Denisova hominin may have co-existed. The existence of this
distant branch creates a much more complex picture of humankind during the
Late Pleistocene than previously thought (Bokma et al. 2012). Evidence has
also been found that as much as 6% of the genomes of some modern
Melanesians derive from Denisovans, indicating limited interbreeding in
Southeast Asia.

Alleles thought to have originated in Neanderthal and the Denisova hominin
have been identified at several genetic loci in the genomes of modern humans
outside of Africa. HLA types from Denisovans and Neanderthal represent more
than half the HLA alleles of modern Eurasians, indicating strong positive
pg. 37
selection for these introgressed alleles.
Figure 10: Dermoplastic reconstruction of a Neanderthal
H. floresiensis
H. floresiensis, which lived from approximately 100,000 to 12,000 before
present, has been nicknamed hobbit for its small size, possibly a result of
insular dwarfism (Brown et al. 2004). H. floresiensis is intriguing both for its
size and its age, being an example of a recent species of the genus Homo that
exhibits derived traits not shared with modern humans. In other words, H.
floresiensis shares a common ancestor with modern humans, but split from the
modern human lineage and followed a distinct evolutionary path. The main

find was a skeleton believed to be a woman of about 30 years of age. Found in
2003 it has been dated to approximately 18,000 years old. The living woman
was estimated to be one meter in height, with a brain volume of just 380 cm3
(considered small for a chimpanzee and less than a third of the H. sapiens
pg. 38
average of 1400 cm3).
However, there is an ongoing debate over whether H. floresiensis is indeed a
separate species (Argue et al. 2006). Martin et al. (2006) hold that H.
floresiensis was a modern H. sapiens with pathological dwarfism. This
hypothesis is supported in part, because some modern humans who live on
Flores, the island where the skeleton was found, are pygmies. This, coupled
with pathological dwarfism, could possibly create a hobbit-like human. The
other major attack on H. floresiensis is that it was found with tools only
associated with H. sapiens.
The hypothesis of pathological dwarfism, however, fails to explain additional
anatomical features that are unlike those of modern humans (diseased or not)
but much like those of ancient members of our genus. Aside from cranial
features, these features include the form of bones in the wrist, forearm,
shoulder, knees, and feet. Additionally, this hypothesis fails to explain the find
of multiple examples of individuals with these same characteristics, indicating
they were common to a large population, and not limited to one individual.

pg. 39
Figure 11: Restoration model of Homo floresiensis
H. sapiens
H. sapiens (sapiens is a Latin word which means "wise" or "intelligent") have
lived from about 250,000 years ago to the present. Between 400,000 years ago
and the second interglacial period in the Middle Pleistocene, around 250,000
years ago, the trend in skull expansion and the elaboration of stone tool
technologies developed, providing evidence for a transition from H. erectus to
H. sapiens. The direct evidence suggests there was a migration of H. erectus
out of Africa, then a further speciation of H. sapiens from H. erectus in Africa.
A subsequent migration within and out of Africa eventually replaced the earlier
dispersed H. erectus. This migration and origin theory is usually referred to as
the recent single origin or Out of Africa theory. Current evidence does not
preclude some multiregional evolution or some admixture of the migrant H.

sapiens with existing Homo populations. This is a hotly debated area of
pg. 40
Paleoanthropology.
Stanley (1998) established that humans are genetically highly homogenous;
that is, the DNA of individuals is more alike than usual for most species, which
may have resulted from their relatively recent evolution or the possibility of a
population bottleneck resulting from cataclysmic natural events such as the
Toba catastrophe. Distinctive genetic characteristics have arisen, however,
primarily as the result of small groups of people moving into new
environmental circumstances. These adapted traits are a very small component
of the Homo sapiens genome, but include various characteristics such as skin
color and nose form, in addition to internal characteristics such as the ability to
breathe more efficiently at high altitudes.
H. sapiens idaltu, from Ethiopia, is an extinct sub-species from about 160,000
years ago.

Figure 12. Current view of the temporal and geographical distribution of hominid
populations.
pg. 41

pg. 42
10.0 HOMO SAPIENS TAXONOMY
The cladistic line of descent (taxonomic rank) of Homo sapiens (modern
humans) is as follows:
Taxonomic
rank
Name Common name Millions
of
years ago
Domain Eukaryota Cells with a nucleus 2,100
Kingdom Animalia Animals 590
Phylum Chordata Vertebrates and closely related invertebrates 530
Subphylum Vertebrata Vertebrates 505
Superclass Tetrapoda Tetrapods 395
Unranked Amniota Amniotes, tetrapods that are fully terrestrially-adapted
340
Class Mammalia Mammals 220
Order Primates Primates 75
Superfamily Hominoidea Apes 28
Family Hominidae Great apes (Humans, chimpanzees, bonobos,
gorillas, and orangutans)
15
Subfamily Homininae Humans, chimpanzees, bonobos, and gorillas 8
Tribe Hominini Genera Homo and Australopithecus 5.8
Subtribe Hominina Contains only the Genus Homo 2.5
Genus Homo Humans 2.5
Species Homo sapiens
archaic
Modern humans 0.5
Subspecies Homo sapiens
sapiens
Fully anatomically modern humans 0.2
Table 1. Homo sapiens taxonomy

pg. 43
11.0 CONCLUSION
Archaic Homo sapiens, the forerunner of anatomically modern humans,
evolved between 500,000 and 250,000 years ago. Recent DNA evidence
suggests that several haplotypes of Neanderthal origin are present among all
non-African populations and Neanderthals and other hominids, such as
Denisova hominin may have contributed up to 6% of their genome to present-day
humans, suggestive of a limited inter-breeding between these species.
Anatomically modern humans evolved from archaic Homo sapiens in the
Middle Paleolithic, about 200,000 years ago. The transition to behavioral
modernity with the development of symbolic culture, language, and specialized
lithic technology happened around 50,000 years ago according to many
anthropologists although some suggest a gradual change in behavior over a
longer time span. It can therefore be concluded that man evolved from lower
primates.

pg. 44
12.0 REFERENCES
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Bill Bryson (2004). “The Mysterious Biped”. A Short History of Nearly
Everything. Random House, Inc. pp. 522–543.
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Hominins". Evolution 66 (9): 2969–74
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