PSYC 101 Lecture Notes - Sickle-Cell Disease, Encephalization, Egg Cell

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Published on 1 Feb 2013
Psych 101, 007
Jan. 15
Chapter 3 Evolution, Heredity, and Behavior
This Chapter: Considering biological basis/ evolution to understand behaviour
The Development of Evolutionary Theory
Natural Selection & Evolution
Heredity and Genetics
For thousands of years, people knew that they could cross-breed animals to get the traits that they want in the animals
(ex. retriever dogs for hunting, varieties of pigeons were produced through artificial selection like Blue grizzle frillback,
English pouter, Indian Fantail)
mutation showed up and people bred that mutation in the species to produce a stable line with that
mutation as a desirable trait
Charles Darwin formulized the Theory of Evolution & Natural Selection
Darwin published The Origin of Species (1859)
3 main ideas: heredity, variability, & natural selection
Heredity= generation to generation
Variability= characteristics across species -> in homo sapiens: eye colour, hair colour, height, personality,
weight, intelligence
Natural Selection= “survival of the fittest” (most successful in competition for resources)
About me and my genes, not about individuals
Those who reproduce are more successful in the long run in an evolutionary sense
Creates survival & reproductive advantage
Darwin’s Theory of Evolution
Living things are dynamic, not static
Evolution is gradual & continuous in slowly changing environment but more rapid changes when sudden change
of environment. Pace of evolution depends on rate of change.
Ex. White coat colour is huge advantage in the Arctic. When snow goes away, white now stands out against the
dirt/green background so white colour becomes disadvantage. The species must change/adapt to survive or die.
All organisms descended from an original and common ancestor -> this notion was the most
controversial/contested when Darwin first published it
changed the way humans thought of themselves
humans no longer separate & different from animals, we were all the same
justifies studying animal behaviour & biology to learn about humans
natural selection also maintains status quo under steady conditions
*There is no scientific evidence that refutes the theory of evolution- there is a great deal of evidence that supports it.
Natural Selection as a Three Step Process: Variation, Selection & Retention
Variation: there are differences in genes in same species, mutations show up
Selection: some traits are advantageous, some are disadvantageous
Retention: species with traits that are advantageous, survive, reproduce,& the gene/mutation stays
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Natural Selection
Survival of the fittest is determined by an individual’s reproductive success
Variation=differences among members of a species in both genotype & phenotype
Phenotype: is what you see about a person
Genotype: inferred from phenotype, can be altered (b/c differences in the environment, womb, nutrition etc.) ,
produced through interaction with the environment
just the genes, like a recipe but a lot of things can change the way of how that recipe comes out
can’t know the height of someone b/c height isn’t coded
Competition-resources (shelter, food, mates) are limited- individuals compete with varying success, those that
win more are more likely to succeed & reproduce
Competition can be within a species or between species
If they need similar resources, animals could change their behaviour. For example, be nocturnal so not directly
competing fir same resources
Sexual Selection
Another type of selection, explains traits that can’t be explained with natural selection
Some traits don’t seem advantageous like peacock tails & antlers, yet they exist in animals, doesn’t make sense
through natural selection
Why would the animals develop those traits when the trait doesn’t help them survive, get food, uses a lot of
energy, etc.
The idea that attractive ones have more offspring
Ex. Male peacock with the most beautiful, big tail is more successful with mating & reproducing, the big
colourful tail tells the female peacock that the male has good genes & is healthy (the male has to be healthy to
grow that tail & survive with it)
In sexual selection, traits are shaped by the choices that influence mate selection- females want to choose
mates that will father the best offspring
Alternative strategies: Arnold vs. Woody, stolen copulations -> happens in deer, fish
Ex. Some male fish mimic the colouring of females, pretend to be females laying eggs, but actually male
depositing sperm, won’t be chased away by another male fish, can reproduce
Two Common Mistakes in Interpreting Darwin
1. Assumption that evolution equals “progress” the difference between better & “better adapted” , evolve does
not equal improve, just means better adapted for a specific direction (more specialized rather than more
advanced or highly evolved), there is no perfecting direction in evolution that we are headed towards
2. Assumption that ‘Survival of the fittest” means “survival of the strongest” rather than survival of the most
Application of Darwinian Theory to Psychology
Realization of common ancestry among animals led to use of rats & other animals of psychological experiments
Determined the position of humans within kingdom, rather than above it
We are not separate & different, we are part of a continuum
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Alternate Theories
Darwin’s theory of evolution in completion with other theories
Lamarck- inheritance of acquired characteristics ex. giraffe’s neck
Adopted theory as policy in the Soviet Union under Stalin- with disastrous results for their agricultural
Human Evolution
2 major factors occurred in human evolution
Bipedalism- ability to move about in environment on 2 legs- 4 million years ago- freed hands for grasping &
Encephalization- increased brain size- began about 2 million years ago- thinking, planning, language, huge
dramatic change in brain size over a relatively short period of time
Modern humans first appeared 40,000 years ago, we are fairly new
Sex is the source of variation- organisms that reproduce asexually make offspring just like themselves
If the environment changes, offspring with exact same genes die if their genes don’t fit well in new environment,
no backup plan
Dominant & Recessive Alleles
Humans and all mammals are diploid. That means they have 2 copies of every gene, one from mother, one from
Sometimes both members of a pair are identical, sometimes they are different- the different forms of a single
gene are alleles
The allele that has the most impact on the phenotype is called the dominant allele- the other is the recessive
Ex. brown eye allele dominant over blue eye allele so you have brown eyes
Sometimes a number of genes influence a trait- this is called polygenic
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