A detailed and scientific discussion on the evolution of human brain, based on blended studies of Bio-psychology and Anthropology.

1. The evolution of human brain:-
Created by: Bidisha Haque

2. Three hypotheses:-
*Epiphenomenal
*Ecological
*Social brain hypothesis

3. Epiphenomenal hypothesis:-
*Brain is evolved due to increase in size. Mental states exist in relation
to some material happenings, but causally are completely irrelevant.
Behaviour is caused by muscles that contract upon receiving neural
impulses, and neural impulses are generated by input from other
neurons or from sense organs.

4. In general, materialist theories are those
subscribing to the statement that mental events can have
no effective action on the brain events in World 1— that
World 1 is closed to any conceivable outside influence such
as is postulated in dualist-interactionism. The term
LIAISON is used for both intention and perception,
particularly in voluntary movement.

5. Ecological Hypothesis:-
*Environmental conditions bounds the brain
for evolution. Here to be considered two
types of consumers-
Folivorous- Leaf consumers.
Frugivorous- Fruit consumers.
Fruit consumers are more
likely to be having more developed brain in terms of
(a) Overall size of brain, (b) Relative size & (c)
Brain’s tendency to use resources. They have also
developed Sustenance of attention & Visuo-spatial
capacity within themselves.

6. Advanced form of Ecological
hypothesis- The Social Brain
Hypothesis:-
British anthropologist Robin Dunbar, who argues
that human intelligence did not evolve primarily as a
means to solve ecological problems, but rather
intelligence evolved as a means of surviving and
reproducing in large and complex social groups.

7. Primate neo-cortex size vs.
Social group size:-

8. Predictive group size & average
brain size in primitive era:-
• Predictive group size • Average brain size

9. Total adjusted amygdala volume in
order to the total number of
people in social network:-

10. Relative size of brain-
inproportionate to their body:-
Homo habilis, the first of our genus Homo who
appeared 1.9 million years ago, saw a modest hop in brain size, including
an expansion of a language-connected part of the frontal lobe called
Broca's area. The first fossil skulls of Homo erectus, 1.8 million years
ago, had brains averaging a bit larger than 600 ml. Early Homo sapiens
had brains within the range of people today, averaging 1,200 ml or more.

11. The adaptation of the body
context in the environment:-
The human body readily responded
to changing environmental stresses in a variety of biological and cultural
ways. They could acclimatize to a wide range of temperature and
humidity. When travelling to high altitudes, their bodies adjusted so that their
cells still received sufficient oxygen. They also were constantly responding in
physiological ways to internal and external stresses such as bacterial and viral
infections, air and water pollution, dietary imbalance, and overcrowding. This
ability to rapidly adapt to varying environmental conditions has made it possible
for us to survive in most regions of the world.

12. Convolution of human brain:-
The human
brain is said to
have more
convolutions
than any other
species on the
planet. There
are many
ridges and
contours
(convolutions
and sulci) in
the human
brain which
result in a
much larger
surface area
than is readily
apparent.

13. Cultural complexity:-
According to
Geoffrey Miller
,human intelligence is
unnecessarily
sophisticated for the
needs of hunter-
gatherers to survive.
the manifestations of
intelligence such as
language, music and
art did not evolve
because of their
utilitarian value to the
survival of ancient
hominids. Rather,
intelligence may have
been a fitness
indicator.

14. Manipulating symbols:-
• A symbol is an object that represents,
stands for, or suggests an idea, visual image,
belief, action, or material entity.
• Human brain can create, use & manipulate
symbols. Symbols help to give structure our
cognition.
• Since the last common ancestor shared by
modern humans, chimpanzees and bonobos,
the lineage leading to Homo sapiens has
undergone a substantial change in brain size
and organization. As a result, modern humans
display striking differences from the living
apes in the realm of cognition and linguistic
expression.

15. Bipedalism:-
• The evolution of human bipedalism approximately four million years ago has led
to morphological alterations to the human skeleton including changes to the
arrangement and size of the bones of the foot, hip size and shape, knee size,
leg length, and the shape and orientation of the vertebral column.It also can
be considered as an evolution of brain.

16. Sexual dimorphism:-
• Sexual dimorphism is a phenotypic difference between males
and females of the same species, meaning that there are
obvious differences between the male and female of the
species. Examples include differences in morphology, size,
ornamentation and behavior.
• Human started to having certain mating period, affection,
affiliation & socialization.
• All hominoids show some differences in size between the
sexes, as well as in such features as the shape of the pelvis
and in crests on the skull. Thus male gorillas weigh perhaps
twice as much as females. This size difference is much less
in chimpanzees and even less pronounced in modern humans,
where on average males are 1.2 times as heavy as
females.This trend towards a lesser degree of sexual
dimorphism can be traced in hominin fossils. The skeletons of
the australopithecines show a marked degree of sexual
dimorphism, which is reduced in the early hominids.

17. Language:-
• Language and the thought that it expresses constitute arguably the most
distinctive feature of human behavior. Controversies pervade not only
speculation about the phylogeny of distinctively human language, but also the
characterization of what has evolved, the linguistic component of the human
behavioral phenotype. There is at least this much agreement about human
language – it is a form of communication that is unique in the natural world
(Hockett, 1960; Bickerton, 1990; Hauser, 1997b; Christiansen & Kirby,
2003a,b).
• Unlike systems of communication employed by other species, human language is
said to have:(1) modality/stimulus independence,(2) duality of patterning, (3)
shared, arbitrary symbols,capable of displaced reference,(4) generalized
systematicity/domain independence,& (5) hierarchical/recursive structure or
syntax.

18. Dunbar’s number:-
• Dunbar argues that when the size of a social group
increases, the number of different relationships in the group
may increase by orders of magnitude. Chimpanzees live in
groups of about 50 individuals whereas humans typically have
a social circle of about 150 people, which is now referred to
as Dunbar's number.

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