1. The Path to Homo sapiens sapiens
Evidence of Connexions Amongst the Primates and
Hominim Ancestors
2. Primate Phylogeny
● Humans are primates and we are more
closely related, both genetically and
anatomically, to chimpanzees than to
any other species
● It is therefore assumed that we share
behavioural and conceptual similarities
with the primates
● This assumption has been highly
significant in psychological studies, and
also in philosophical inquiries—the
similarities in brain structure and
perception, an inheritance of our distant
evolutionary past, may bring inherited
patterns of thought and perception
● The work of Carl Jung and Sigmund
Freud returned to this point regularly,
but even phenomenological studies
have flirted with the existence of
common thoughts and perceptions
governed by our senses and physiology
3. The Oldest Primates
● The oldest anthropoid fossil known
dates from ca. 35 million years ago
and derives from Thailand and is
called Siamopithecus eocaenus
● It weighed roughly 7 kg, being roughly
the same size as a modern gibbon
● This species shares many similarities
with ancient primates in Africa,
suggesting a broad distribution of
primates across southern Asia
● In Africa, the oldest primate is that of
Aegyptopithecus, which resembled a
modern lemur in size
● Surviving teeth from both species
suggests that they were primarily fruit
eating animals living in the trees
4. Proconsul africanus
● Proconsul is one of the best
represented Miocene hominims in the
fossil record
● It lived from approximately 23 to 14
million years ago
● From the full arrray of remains it has
been shown that there was
considerable variation in this genus
Body sizes ranged from that of a small
monkey (10 pounds) to that of a female
gorilla (150 pounds)
● They also inhabited a wide range of
environmental niches: this included
open woodlands as well as dense rain
forests and it is believed that perhaps
some were partially terrestrial
● This is regarded as crucial for later
evolution, insofar that they could cope
with a broad spectrum of environmental
conditions
5. ● They exhibit the typical Old World
anthropoid dental pattern of 2-1-2-3.
Proconsul also has the typical 5-Y
pattern of cusps seen in the lower
molars of hominims
● Their teeth also consist of a thin layer
of enamel which suggests that they
were probably fruit eaters
● Brain size estimates show that their
brains were as large or larger than
contemporary Old World monkeys
though probably not as large as
contemporary hominims
● Collection of fruit, roots and nuts on
the ground was a probably aspect of
their subsistence
● It is perhaps this trend towards
spending time on the ground that
triggered a movement towards
bipedalism
6. Sivapithecus
● Sivapithecus is a genus of extinct
primates, dated from 12.5 million to 8.5
million years old
● They are known from India and Pakistan,
the first specimens having been found in
the 19th century
● Sivapithecus was about 1.5 metres in
body length, similar in size to a modern
orangutan
● Some specimens were considered to
represent Ramapithecus, another species,
but they are now regarded as Sivapithecus
● The shape of its wrists and general body
proportions suggest that it may have spent
a significant amount of its time on the
ground, as well as in trees
● It had large canine teeth, and heavy
molars, suggesting a diet of relatively
tough food, such as seeds and savannah
grasses
8. Inferences of Chimpanzee-Human Divergence
● Approximately six percent of human
and chimpanzee genes are unique to
those species, but we share over 99%
of our genetic material with them
● Most of the big differences between
human and chimpanzee DNA lie in
regions that do not code for genes
● Instead, they may contain DNA
sequences that control how gene-
coding regions are activated and read
● Studies looking for stretches of DNA
that were highly conserved amongst
chimpanzees, mice and rats were
then compared those sequences to
the human genome sequence, to find
pieces of DNA that had undergone the
most rapid change since the
ancestors of chimps and humans
diverged about five million years ago
9. Genetic Divergence and Brain Development
● This resulted in the discovery of 202 'highly
accelerated regions' or HARs, which
showed a high rate of evolution between
humans and chimpanzees
● Only three of those regions contain genes
that are likely to encode proteins
● The most dramatically accelerated region,
HAR1, appears to make a piece of RNA
that may have a function in brain
development
● The other highly accelerated regions do not
appear to code for genes at all, but many
are located close to genes involved in
controlling when other genes get made, or
in growth and development
● A genetic change, therefore, possibly
occurred that triggered brain development
in hominids leading to our line which was
not shared with chimpanzees
10. Dating the Divergence
● The evolutionary split between human
and chimpanzee may be much more
recent, and much more complicated, than
has previously been thought
● The results of some genetic studies show
that the two species split no more than
6.3 million years ago and probably less
than 5.4 million years ago
● Moreover, the speciation process was
unusual, possibly involving an initial split
followed by later hybridisation before a
final separation
● The time of from the beginning to the
completion of divergence between the
two species ranges over more than 4
million years across different parts of the
genome
● This range is much larger than had been
expected according to assumptions made
on the basis of the fossil evidence alone
11. An Earlier Divergence than Supposed ?
● The youngest regions are unexpectedly
recent, being no more than 6.3 million
years old and probably no more than 5.4
million years old
● This finding implies that human-chimp
speciation itself is far more recent than
previously thought
● If one looks only at the X chromosome, it
almost entirely falls at the lower end of
the time frame
● The estimate that humans and
chimpanzees probably split less than 5.4
million years ago is more recent by ~1 to
2 million years than a previous estimate
of 6.5 - 7.4 million years based on the
famous Toumaï hominid fossil The cranium of Sahelanthropus
(Sahelanthropus tchadensis), which has tchadensis, which is commonly
features thought to be distinctive to the regarded as on the evolutionary
human lineage trajectory of humans
12. ● It is possible that the Toumaï fossil is
more recent than previously thought,
but if the dating is correct, the it would
precede the human-chimp split
● The fact that it has human-like features
suggest that human-chimp speciation
may have occurred over a long period
with episodes of hybridization between
the emerging species
● The possibility of 'hybridization'—that
is, initial separation of the two species,
followed by interbreeding and then final
separation—would also explain the
strange phenomenon seen on
chromosome X
● Interbreeding is known to place strong
selective pressures on sex
chromosomes, which could result in a
very young age for chromosome X
13. Genetic Inversions
● By comparing the human genome with
that of the chimpanzee, it has been
discovered that chunks of similar DNA
that have been flipped in orientation and
reinserted into chromosomes are
hundreds of times more common in
primates than previously thought
● These large structural changes in the
genome, called inversions, may account
for much of the evolutionary difference
between the two species
● They may also shed light on genetic
changes that lead to human diseases
● Researchers can now readily identify
the differences between the human and
chimp genomes Inversion of DNA segments between
chimpanzee and human chromosomes (blue
● These differences lend insight into how lines). One inversion on the end of human
primates evolved, including traits chromosome 7 that sometimes occurs is the
specific to humans ancestral orientation found in primates (order
of dots is yellow-green-red)
15. Comparative Anatomy
● The anatomical similarities amongst
the primates has long been
recognised
● This extends to many different
aspects of the body, from the
disposition of the muscles to the
general shape of the joints, pelvis,
and so on
● It is, however, the pelvis and vertebral
column that has elicited the most
interest from specialists as the
similarities and differences here are
vital to understanding how bipedalism
might have emerged
● Also, there is particular interest in the
development of the hand (to grip
tools) and evidence for brain structure
which is important in studying higher
cognitive functioning
16. The Pelvis
● A study of the pelvis is not only
important for understanding changes
in locomotion, gait and so forth, but
also for the ease of birth
● In chimpanzees, the hips are narrow
and long, which has the result of
spreading the legs out and also
having the femur project downward in
an almost straight fashion
● Early hominims, such as
Australopithecine, had broader hips
and this made the femurs project
downward at an angle towards the
knees
● This was associated with the
development of bipedalism, but also
introduced complications in the
delivery of children—especially as the
cranium became larger
17. Feet and Hands
● The feet and hands show great
similarity, but again, the greatest
correspondence exists between
humans and chimpanzees
● Most notable is that chimpanzees
have opposable thumbs, allowing for
a precision grip necessary to
manipulate tools for fine work
● Humans, however, have lost the use
of the big toe and the foot digits to
grasp objects and to wrap around tree
limbs and such
● This represents an adaptation that
occurred as hominims left the trees
and became bipedal—the need for
such grasping limbs became less and
less and it is suspected that natural
selection resulted in the loss of this in
favour of a foot better suited to
walking and running
20. Higher Primates
● The distribution of the higher primates
that are most closely related to Man
closely parallels that of the earliest
fossil specimens of species that led
towards the emergence of modern
humans
● All of these primates inhabit jungle
environments, but our forebears
(discussed earlier) seem to have had
a broader subsistence spectrum
which involved the collection of food in
more open land
● It is the trends towards foraging in
open land, rather than remaining in
trees, which seems to have favoured
the development of bipedalism
● Nonetheless, as these primates are
our nearest extant relatives, we can
look at their behaviour and draw
inferences concerning basic behaviour
of our ancestors
21. Communication
● Primates have very expressive faces
which convey a vast quantity of
information and is used for
communication
● In human populations, body language
and facial expressions account for
approximately 60% of all
communication
● Almost all verbal communication is
modified by body language in one
capacity or another
● It is not only the facial expressions
which chimpanzees use to convey
information and communicate, but also
body posture
● This is, of course, not unique in the
mammal kingdom as most animals
have specific stances and facial
expressions denoting fear, aggression,
submission and contentedness
22.
23. Range of Expressions
● What is unique about primate facial
expressions and their ability to convey
information is their range
● This is possible only because of the
plasticity of the face and the existence
of muscles differently developed from
those of, for example, canines and
felines
● Moreover, it implies a sophisticated
grasp of not only many visual cues but
also an empathetic appreciation of the
meanings
● This necessarily involves higher brain
functions, to integrate so many visual
signals and also to immediately
recognise their meaning
● Other animals tend to rely on a
smaller range of signals and scents
24. Vocal Communication
● We also share similarities in vocal
communication, but again this is not
unique to primates as most other
mammals signal one another through
sounds
● However, the chimpanzees have not
only instinctual sounds that designate
danger, aggression and submission,
but also use sounds to communicate
information in collective hunting
expeditions
● Moreover, chimpanzees have
distinctive 'hoots' which permit others
in the group to recognise them
individually
● Higher status chimpanzees 'hoot'
more than junior members of the
group, perhaps indicating that vocal
communication is associated with
status
25. Signals and Gestures
● Given the limited range of sounds that
a chimpanzee can make, they rely
equally as much (or perhaps more) on
gestures and signals
● Hand and limb gestures are used,
along with the 'hoots', in organised
hunting expeditions
● A successful kill is signalled by a loud
and excited 'hoot' and the entire group
recognises this and ceases the
hunting, re-grouping
● Most gestures are, however, involved
in social bonding and status
maintenance or assertion within the
group
● Grooming is particularly important, to
strengthen bonds amongst the
chimpanzees in the group
26. 'Linguistic' Capacity
● Washoe was a chimpanzee who was
the first non-human to learn to use
some of the signs of a human language,
that of American Sign Language
● She also passed on some of her
knowledge to her adopted son, Loulis
● It is reported that Washoe could reliably
use about 250 signs
● This test demonstrated 'that the
chimpanzee subjects could
communicate information under
conditions in which the only source of
information available to a human
observer was the signing of the
chimpanzee;' 2) 'that independent
observers agreed with each other;' and
3) 'that the chimpanzees used the signs
to refer to natural language categories,
for instance, that the sign DOG could
refer to any dog, FLOWER to any
flower, SHOE to any shoe'
27. Tool Production
● One of the most significant
discoveries was in October 1960
when Jane Goodall observed the use
of tools among chimpanzees
● Recent research indicates that
chimpanzee stone tool use dates to at
least 4,300 years ago
● Other primates have also been known
to use tools, such as orang-utans and
gorillas, but also non-primates such
as birds
● The tools of the chimpanzees are,
however, the most diverse and
sophisticated
● Stone tools to open nuts and grind
plant material are known, as well as
the use of sticks to extract termites
and other insects along with
sharpened sticks used as spears
28. Transmission of Knowledge
● The capacity to produce certain tools
was transmitted within a social group,
and it appears mainly from the mother
to its offspring
● Of the groups studied in West Africa,
each had its own particular style of
producing tools
● Existence of different traditions seems
equivalent to the subtle stylistic
distinctions that can be seen in the
early tool-kits of hominims in East
Africa
● This is clearly expressed in the stone
tools and form of termite sticks
● In experiments with chimpanzees in
captivity, the offspring must learn a
new tool production technique before
two years of age or thereafter does
not seem able to acquire the skills
30. Interpreting Hominim Behaviour
● The behaviour of the hominims in
East Africa, and those that evolved
from these and expanded into Asia
and Europe, has been interpreted as
being similar to that of the
chimpanzees but becoming more
elaborate through time
● This has led many to use
interpretations based on chimpanzee
behaviour and simple hunter-gatherer
people
● It is not to imply that the hunter-
gatherers are living fossils, but the
group dynamics and adaptations are
thought to share broad patterns with
those of the hominims
● We must, however, recognise that
culture also drove adaptations and
evolutionary developments
31. Social Dynamics
● The social dynamics of chimpanzee
groups and hunter-gatherers in
marginal environments is based on
the extended family
● An hierarchy exists in these groups,
but only insofar that there is a
dominant male
● This is not, however, a closed
network for individuals join and
leave the group
● Such occurrences increase the
chances of success in long-term
survival, for a closed network would
result in inbreeding and probably
lead to the reproductive failure of the
group
● A loose conception of territory also
prevails in these small groups,
where there is privileged access to
resources
32. Tool Production
● Based on the evidence afforded by
chimpanzees, and the ethnographic
evidence of hunter-gatherers, tools
convey social meaning and reflect
social identity
● A wide range of tools were likely
produced, but only those made from
non-perishable material survive for
archaeological analyses
● Skills to produce these tools were
probably learned within the group and
it may be that, like chimpanzees, early
hominims acquired these skills from
the mother at an early age
● A tremendous conservatism in tool
production is evident in the
archaeological record, and this may
have much to do with the method of
technological transmission
33. Subsistence
● The occupation of the jungle margins
or savannah rendered it important for
early hominims to have as flexible a
subsistence regime as possible
● A fundamentally terrestrial existence
would have recommended the
collection of plant foods from the
ground or at a relatively low height in
the trees
● Hunting and scavenging were likely
more important to our ancestors in
East Africa than it is to chimpanzees,
given the environment which they
occupied
● This may perhaps imply that group
hunting was also more important, and
therefore, that communication was
vital
● We shall return to these questions
frequently in later lectures
