slide 1chapter 1 – evolution, heredity and behaviour chapter 3 evolution, heredity, and behaviour

Chapter 1 – Evolution, Heredity and Behaviour Slide 1

Chapter 3

Evolution, Heredity, and Behaviour


Darwin proposed the idea of biological evolution … the notion that populations of organisms change over time in a manner that ends up making them more suitedto their environment

This has lead scientists in many areas (but especially biology and psychology) toconsider the adaptive significance of the physical and behavioural characteristicsof their subjects

A distinction is often drawn between:(1) ultimate causes - events and conditions which, over generations, have shaped the behaviour of our species, versus(2) proximate causes - immediate environmental variables that effect

behaviour

Steve’s “Its really a woman’s world” example

Evolution Theory


Collected many species of animals during his voyage on the “Beagle” and sentmany of the specimens back to England for later study

Was fascinated by how well animals and plants seemed adapted to their environment

Also became interested in artificial selection … a procedure by which certainanimals are mated to produce offspring with desirable characteristics

Wondered if a similar process might also occur in nature … a natural selection

Began collecting data to support his theory of natural selection … but did notpublish his ideas or data for 20 years … until prompted by finding out that somebody named Wallace had a similar theory

Published his ideas in a book called “Origin of the Species” … a best seller then,and now

Brief History of Darwin


The 4 basic premises of Darwin’s theory of evolution

1) The plant and animal communities of the world are dynamic, constantly changing the physical and behavioural characteristics

2) Evolution is gradual. Changes arise through slow and steady environmental changes. Sudden changes challenge a species’ ability to adapt

3) All organisms descended from a single common ancestor. Over time, different species evolved, each adapted to their own ecological surroundings

4) Natural selection not only causes changes during changing environments, it also prevents changes during static environmental conditions

Us versus the whales example

Premises of Evolution


While “survival of the fittest” is part of evolution theory … fit does not meanphysically fit. Rather fitness is defined in terms of reproductive success whichis measured as the number of viable offspring an organism can produce relativeto the organisms that it competes for resources with.

Two processes affect changes to a species

1) Variation - individuals vary in terms of their physical and behavioural characteristics. This variation is often discussed in terms of differences in genotypes (an individuals genetic make-up) and phenotypes (an individuals physical characteristics and behaviour

phenotypes are the result of the interaction between an organisms genotype and its environment

2) Competition - competition for food and mates is critical for insuring natural selection. If there were no competition, fitness would not matter

Process of Natural Selection


Does natural selection apply to humans as well as to other animals?

There is now strong genetic evidence that we have a common with the gorillas and chimpanzees

Steve, show that time line thing here, and mention “Clan of the Cave Bear”

As a species we are somewhat “out of control”. Our strong evolutionarysuccess can be linked to two events in our past:

1) Development of Bipedialism - thereby freeing up the hands for all sorts of mischief (e.g., tool making, weapons, building in general)

2) Encephalization of the Brain - The larger brain allowed more brain area to be expended on cognitive operations like thinking, reasoning, and decision making

another important things it allows is planning … the ability to plan for and predict future events … oh, and language too!

Natural Selection in Human Evolution


Genetics and Heredity

Darwin’s work lead the way to new fields of researchincluding genetics, the examination of the structure andfunction of genes, including the manner in which genesare passed between generations

Included in this is the study of how genes affect an organisms physical and behavioural makeup

Related to this is the issue of heredity, the sum of the traits and tendencies inherited from one’s parents, grandparents, and so on


Basic Principles of Genetics

“Genes are segments of genetic material called DNA(deoxyribonucleic acid) - strands of sugar and phosphatethat are connected by nucleotide molecules of adenine,thymine, guanine, and cytosine”

DNA is in the form of a twisted ladder, with the sugar andphosphate forming the sides, and all those nucleotide thingsforming the rings

The sequence of the nucleotide molecules directs theprotein synthesis that control the biological and physical development of the body … and behaviour??

> cool book … “The Double Helix”


Heredity, Variability, & Chromosomes

Genes are located on chromosomes, and each chromosomecontains a different sequence of genes

We inherit 23 chromosomes from each of our parents,giving us 23 pairs. Different pairs control different things,for example one pair determines gender characteristics

Sexual reproduction involves the union of a sperm and an ova … each of which are formed through a special form ofcell division called meiosis

The 23 pairs of chromosomes split into two groups with onemember of each pair joining each group … allowing for223 or 8,388,608 different combos of sperm or ova per person … allowing 70 trillion possible kids per couple!!


What’s the Big Deal About Sex?

The vast majority of organisms reproduce via a sexualprocess of some sort … why sex??

As seen by the previous “couple” number, the need fortwo individuals to jointly create one greatly increases thegenetic diversity of the organism … make it more ableto evolve if evolution is necessary

Nasty bug example - yuck!


Genetics and Psychology


Genetics and Psychology

The image to the left is a colorblindnesstest - colorblindness is determined primarilythrough genetics … can you see the shapes?

OK, now for another example … the taste test!

The moral? Our perception of the world is largely determined by our genetic make-up. How far dogenetics go in explaining human experience and behaviour?


The Example of Alcoholism

Alcoholism can obviously be a very destructive“disease” … how much is it due to genetic factors?

Twin Studies -

Concordance rate for alcoholism is higher for MZ thanfor DZ twins (76 vs 61 for males, 36 vs 25 for females)

This is true even when the kids are not raised by theirbiological parents


The Challenge of Altruism

As a final look at Evolution Theory, let’s consider the challenge that is posed by altruistic behaviours

An altruistic behaviour is one in which an organism does something that puts itself at risk, in order to aid another

Many animals (including humans) perform altruistic acts - for example, howling wolves warning of predators

Surely these behaviorsdefy the notions ofEvolution Theory, right?

Turtle soup chef coming!!Run for your lives!! Ahh!!


First Reply to the Challenge - Inclusive Fitness

Hamilton (1964) argued that evolution is not really focusedon the reproductive success of the “individual” but ratherfocuses on the reproductive success of the “gene”

Often times, altruistic acts are directed towards close family members who share many of the same geners … especially towards children

Thus, although the altruistic act may hurt one individual carrying a certain gene, in doing so it may serve the “greatergood” of preserving the same genes in related individuals

This notion is termed inclusive fitness


Second Reply - Reciprocal Altruism

But not all altruistic acts are directed at family members,what of the acts directed at total strangers?

Trivers (1971) claims that Evolution Theory also has ananswer to that … reciprocal altruism

This notion is that an individual considering performingan altruistic act towards a stranger will do so if thepotential benefits of the acts outweigh the risk

If the benefits do outweigh the costs, then the individual can increase their reproductive success by performing theact and does so … a somewhat dark view of altruism eh?


Summary of Chapter 3

There is no doubt that our genes affect the manner in whichbe perceive and relate to the world around us

Evolution Theory provides a theoretical framework forunderstanding (a) how we as humans have come to be as we are and (b) why we may act as we do in certain situations

Often, when one proposes a theory of human behaviour, they include some discussion of their theory in terms ofEvolutionary Adaptiveness … e.g., inhibition of return


Inhibition of Return Example

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Subjects are faster when the target is in a new area of thescreen, than if it is in the area that was flashed, why?


slide 1chapter 1 – evolution, heredity and behaviour chapter 3 evolution, heredity, and behaviour

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