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Neurological Basis of Behavior (PSY - 610)

Lesson 07

EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR

Objective:

· The concepts of evolution and its developmental process.

· Evolution of the homosapien to understand brain development and behavior changes as they

evolved.

Important developments of Homosapien development

Stereoscopic vision

Vision for seeing depth is more specialized. This reduced dependence on smell (early mammalians

developed smell as a strong evolutionary change to compete with dinosaurs). In the evolved primate

vision not olfaction became the primary sense especially depth perception and distance vision ( in

upright posture ) worked very well for hunting and locating prey across longer distances.

Bipedalism

Pelvic bones of early ape man underwent a change. The pelvic is shorter in length and wider in man.

This is to give support for upright posture and balance. However, this is longer in Ape and thinner as

this supported the bent posture. Bipedal running emerged earlier in the man ape (and even in the higher

primates) before walking. Walking is an efficient method of covering long distances without exhaustion.

Apes can outrun man in short distances, but on longer distances man wins as he can continue. This is

why man became a more efficient hunter,

Why bipedalism is an important change. It is important as

a) Walking and maintaining stamina over long distances enabled man ape to cover l more hunting

grounds

b) Hunting efficient as it allows the walker's hands free for tools! (Tool use and bipedalism emerged

around the same time).

This has been seen as a most important development by Darwin: Tool use the cause and effect of

bipedal locomotion.

There were other major developments relevant to the brain and behavior.

Skull and brain size: increase in brain size, indicating that there were developments in

specialized functions as well as growth in the size of the brain, neurons, and cells. This system

became more evolved.

Increased cortex: In lower animals the cerebral cortex primarily has sensory-motor functions,

whereas in man the functions of the cortex have become more specialized. Sensory motor

functions are reduced and higher order functions such as association have evolved in the cortex.

The cortex has taken over as the master control in humans.

Thumb: The separation of thumb from finger is a major development. In apes we see in less

evolved primates. However, this is larger and separated in man, making the hand more efficient

and useful for grasping and efficient tool use. These are prehensile hands.

Neurological Basis of Behavior (PSY - 610)

Language evolved in humans as a strong means of social and other communication, visual cues

no longer remain that important. This language can easily learnt by infant by being with the

caretaker (usually mother). Language also sharpened the capabilities of homo sapien for

planning, foresight, language, art and culture.

Teeth and jaw (and forehead) development: In baboons and other apes the size of the canine

is different for males and for females. The males have much larger canines as they are the

fighters. Their canines are used to threaten (through display), attack, hold, shake, pierce the

enemy. Females have smaller canines as there is no need for a fight against predator. So we see

a reduced canine size with development of differentiation of the female role. Further, the jaws

moved to a point where the jaw bone's position with reference to position of the vertebral

column moved for balance the body for support of bipedalism. The forehead slope is also

reduced. The facial appearance is less brutish.

Family evolved: Since the females carry the young in utero for the period of gestation, the

female role/investment and involvement is greater with infant. The female has to remain with

the infant cannot move around freely while carrying the young- both can be endangered.

Therefore the male role as hunter evolved. Sexual dimorphism has evolved, to keep family

together and for protection of the offspring.

Social groups: Since male hunting alone would be vulnerable to predators, therefore hunting in

groups evolved females nursing stay behind. Males hunting together would also be able to hunt

large animals food would last longer. Thus, social living was evolved first in the caves. There

was food sharing, increased social contact which led to increased use of language and signals.

Reduced fat deposits on body as there was not much need to store food and also discovery of

fire and fur coverings also reduced the need for fat to keep the body ready for times of

starvation and cold. There was also reduced hair on the body perhaps as this created impediment

in running. Since body hair was reduced, specialized sweat glands for rapid diffusion of heat

were evolved.

Improved power of stereoscopic vision and other functions: This was most beneficial (as

described earlier) but along with this came other benefits and evolvement. Since longer

distances could be seen standing, there was development of perception and memory. These

became important for remembering food sources and water holes (and predators to watch out

for).

Evolution of the human brain

There is a rapid growth in both size and intellectual functioning. However, the growth in intellectual

capacity was more important. In comparison elephants (8000cc) and whales (5000cc) have

bigger/heavier brains than man (1300cc). Genius brains are not different from common men. The total

brain size may not be the critical issue. It is the growth of the cerebral cortex its size has grown

enormously and it has taken over the functions form lower (and earlier evolved areas). The cerebral

cortex ahs grown so much that it has to be folded to fit into the cranium. Thus, convulations (folds),

deep grooves are formed to fit in more cortexes in a small cranium case! The Cerebral cortex has taken

over association functions, not only sensory or motor functions. The higher the animal on the

evolutionary scale the greater the control of the cerebral cortex, homo sapien being the highest evolved

primate therefore has at the highest degree of encephalization.

What has evolution to do with psychology?

Evolutionary psychology have been studying the evolvement of a wide range of human and other

behaviors such as monogamy, polyandry, gender roles. These studies provide insights into the most

complex social and other human behaviors. These behaviors have resulted from adaptations of millions

of years

Neurological Basis of Behavior (PSY - 610)

· Behaviours of all animal kingdom evolved and similar

· Evolution-influences genes---gene programmed for neural development need interaction from the

environment/ experience. Brain continuously interacting with environment, whatever is successful

is passed on to next.

Man's rate of biological evolution may have been slowed, but social/cultural evolution increasingly

complex and fast...where are we going? Speculate. Points to ponder and think!

The Nature or nurture debate keeps coming up in research and discussions among scientists working in

behavioural neurosciences. In order to answer this we must remember that a) behaviour occurs in

relation to some event i.e. it has to have an interaction with the environment, affect it and be affected by

it, b) organism comes already equipped to face the world in a particular manner, i.e. is programmed

"genetically determined animal possessing biological structures and capabilities and limits"

Thus, behavior is genetically determined as well as exploited when an appropriate environment is

provided. Some behaviour is completely determined while others are somewhat determined whereas

there are some which are not at all controlled by genes. The range of behaviours extends from

completely innate to completely learnt. In the lower animals such as fruitflies the behaviour is carried

out as per genetic programming in response to the environmental cues. On the other hand in humans

language apparatus is biologically developed, but languages are learnt (language which is taught to the

growing child depends on the environment he is raised in). Similarly culture and traditions are not

biologically determined.

The continuum below shows that in lower animals and simpler organisms behavior is innately

determined, whereas in humans there are some completely learnt

Innate (completely determined)------------------------------------Only learned

Fruitflies-------------------------------------------------------------------------------human languages

The question is do genes produce innate behaviour? The answer is No; they only provide templates for

synthesis of appropriate proteins, protein chains and timing of release. There is programming of genetic

proteins and chains which determine the brain program and developments which can flourish in a

certain environment. The triggering cues for genetically programmed behaviors come from the

environment. These can be cues from the external environment e.g. External cue could be lion hunting

for food; deer sees the lion it runs to save itself. The internal cues come from within the organism's

systems the hormones, the needs and the signals form these lead the organism to action. For example,

internal cues may be signals for food/nutrition; the animals feel hungry and seek food. If there is rise in

the prostaglandins levels birds start nest building. There can also be a combination of both the external

and internal cues, that you see food or smell food and immediately feel like eating.

Can experience affect innate behaviour? Yes, in some cases it can. Mothering behaviour is due to

hormonal changes after birth. However, we cannot induce mothering with drugs only, unless this has

been experienced earlier (naturally). This experiment was carried out with ring doves.

Reference

Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

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