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PSYCH 1XX3 Chapter 2: Evolution (Full Notes)
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  • April 22, 2024
  • 5
  • 2023/2024
  • Class notes
  • Michelle cadieux, joe kim
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Chapter 2: Evolution

Evolutionary Psychology: The pursuit of psychological science with discriminating in mate choice than their male
explicit attention to contemporary knowledge and theory about the counterparts (bad choices are more costly to
evolutionary process females, who must make a major investment in
● Biology = science of life, theory of evolution = unifying each successful offspring)
conceptual framework of biology Concept of Evolution: Populations of organisms evolve in various
● Our brains = part of biology = subject to the forces of ways over generations (evidenced by dating fossil records of extinct
evolution like all living things species)
● Psychological study: ● Phylogeny: A method for understanding the history of
○ Male Students: Recruited to be ‘odour donors’+ evolution through the tracing of changes in species over
given fragrance-free soap to shower with, and time
clean T-shirts to wear on two consecutive nights, ○ Phylogenetic Trees: Can be constructed on the
each volunteer was told to sleep alone + refrain basis of anatomical structures and/or DNA
from eating garlic and spices, after two nights, sequencing
they were to seal their T-shirts in a zip-lock bag ● Major evolutionary changes occur over long periods of time,
and return it to the lab however, many evolutionary processes can be directly
○ Female Students: Recruited to sniff the contents of observed and used to support evolution since rapid changes
the plastic baggies and rate the odours considering also occur
their intensity + ‘pleasantness’ ● Adaptive Radiation: Diversification of a group of organsims
○ Molecular Genetic Techniques: Used to determine into forms filling different ecological niches, demonstrated
the students’ genotypes with respect to three by Darwin’s finches (ie. woodpecker finch, vampire finch)
particular genetic loci, namely members of the ● Additive Microevolution = Big evolutionary changes
Human Leukocyte Antigen (HLA) group (also ● Can occur by natural selection, mutation, genetic drift,
known as Major Histocompatibility migration
Complex/MHC) genes Evolution by Natural Selection: Variation affects survival and
■ These genes play a role in immune reproduction through the heritability of traits; useful traits are selected
function + were known to affect body and allow for reproduction and survival and through this propagate
odours in mice and other mammals themselves into the future, called descent with modification
■ Men chosen were genetically similar or ● First evidence for natural selection came from Darwin’s
dissimilar to the rater in their MHC observations of the changes in physical characteristics +
profile behaviours of finches across the Galapagos Islands
■ Women were divided based on if they ● Natural selection is non-goal-directed, but often a stabilizing
were taking oral hormonal process
contraceptives ● Stabilizing Selection: Selection against any sort of departure
○ Results: Naturally cycling women (not taking ‘the from the species-typical adaptive design, tends to keep traits
pill’) rated odours of men genetically dissimilar to stable over generations, may cause rapid evolution
themselves as significantly more pleasant but ● Three essential components of natural selection:
women taking the pill showed the opposite effect ○ Variation: There are significant individual
(rated genetically similar men’s odours as differences among individuals for any given
significantly more pleasant) characteristic in a population
○ Hypotheses Behind Study: Derived from ideas ○ Differential Reproduction: These differences
about the evolved functions/purposes of women’s affect individuals’ chances of surviving and
reactions to male odours reproducing (some individuals will have more
■ First Idea: A woman’s choice of a mate offspring than others)
can be influenced by her affective ○ Heritability: Traits that give rise to differential
responses to male odours reproduction have a genetic basis (offspring of
■ Second Idea: There is a potential cost successful reproducers will resemble their parents
associated with being attracted to people with respect to these variable characteristics)
whose MHC genes are similar to your Adaptations: A process by which organisms become better suited to
own (elevated likelihood of producing their environment + increase their fitness (ability to survive +
offspring with less versatile + weaker reproduce)
immune systems) so natural selection ● Phenotypes: Observable characteristics (including
should have favoured preferences for appearances and behaviours) of an organism resulting from
partners dissimilar in this aspect of their the interaction of genotype + environment
genetic make-up ● Daphnia Example: To avoid predators, they engage in
■ Third Idea: Taking oral contraceptives phototactic behaviour (if sun is visible, they sink lower in
puts women in an infertile the water to avoid being seen, when the sun has set, they
psychophysiological state in which their float closer to the water’s surface to feed)
affiliative preferences no longer reflect ○ Threat/chemical cues of nearby predators causes
an evolved strategy for screening them to stay closer to the water’s surface even
potential mates, but instead function in where there is light out
the realm of social support ■ This flexible phototactic behaviour itself
○ Why Male Odour Donors?: Because women (like evolved as a function of the risk of
most other female mammals) are typically more predation

, Chapter 2: Evolution

○ Offspring hatched from eggs laid by Daphnia ● Attraction: A factor of the sex of individuals: their gamete
when there were no fish in the pond responded sizes and differential parental investment
less to light (stayed closer to the surface) in the Cues: Different sexes look for different cues of reproductive
presence of fish chemical cues than did offspring ability/fertility to find a mate of the best quality for gene transfer
hatched from eggs laid by Daphnia when there ● Fluctuating Asymmetry: A measure of bilateral (left vs.
were fish in the pond right) traits that are symmetrical over the population as a
○ This means that Daphnia with genes that caused whole, but not necessarily symmetrical for any given
them to behave phototactically in the presence of individual
fish predators were more likely to survive to lay ○ Lower fluctuating symmetry = more desirable
eggs than Daphnia with genes that did not cause ○ Indicative of health and robustness towards
such phototactic behaviour environmental hardship (symmetry decreases
○ Conversely, when there was no threat of when faced with hardships/health issues)
predation, Daphnia with genes that did not cause ○ Healthier Individual = Better choice of mate
them to behave phototactically in the presence of because 1) they might be able to pass along the
fish predators were more likely to survive to lay genes that helped keep them healthy to their
eggs offspring and 2) they might make better long-term
Functionality: The functions of adaptations are often inferred from mates since they can stay around longer and in
their operations and corresponding hypotheses that have been better condition to help rear and support offspring,
empirically tested (hard to identify) hence, cues of health in general might be desirable
● Selectionism: Adaptations don’t serve simply to increase in a prospective mate
aspects of overall well-being, rather, they serve to increase ○ Feminine/Masculine Appearance: Consequence of
fitness (the relative reproduction of an individual’s genotype differences in hormones that women and men
as a consequence of its traits) have been exposed to over development, men =
○ Our current traits exist because they have been more testosterone during development, women =
inherited from ancestors with better reproductive more estrogen, these hormones affect fertility,
success (better genes lead to greater chances of physical strength and physical appearance
survival and reproduction) correlated with biological sex
● Adaptations are not continuously advantageous (as the ■ Ie. The waist-to-hip ratio (circumference
environment changes and they can lag behind) + they are of waist divided by circumference of
not perfect (just more optimal for the environment in which hips) is strongly sexually dimorphic–
they developed then other traits performing the same task) women tend to have much narrower
Sexual Selection: Sexual selection and the resulting differential waists, relative to their hips, than men
reproduction is a special form of natural selection based on do (lower waist-to-hip ratios = more
competition to mate and reproduce, represented by preferences by one estrogen = more fertile)
sex for particular characteristics in the opposite sex, may even benefit ● Cues that predict Attractiveness: Fluctuating asymmetry,
fitness at the risk of mortality (ie. Male peacock tail= beautiful but apparent health and masculinity/femininity
heavy to lug around) Infidelity: There exists increasing uncertainty from men about
● Intrasexual Selection: Competition among individuals of offspring as they have less reliable cues than females and face greater
one sex over access to the other sex (same sex interaction) costs of investing in the offspring of other males
● Intersexual Selection: Competition to capture the interests of ● As a result of differential investment and paternal
the other sex (interaction between sexes) uncertainty, there exist differential responses to infidelity
○ Mate Choice: Selection of a mate depends on the ○ Men are more prone to sexual jealousy (feelings
attractiveness of their traits of anger + desire to guard a mate/sexual prospect
● Reproductive Differences: Affect the evolution of sexual from engaging in sexual activity with potential
psychology and differences in attraction rivals)
○ Males= small gamete (sperm) + benefit from ■ Designed by natural selection to reduce
a man’s risk of cuckoldry
attempting to reproduce more often than females
■ Often the reason for domestic assault
since they can re-enter the mating ‘pool’ more
and homicide by men
often, females = large gamete (ova) + invest more
in reproduction (gestate, feed, nurture offspring, ○ Women are more prone to romantic jealousy
often without any help from males) (feelings of anger + desire to guard a mate/sexual
prospect from leaving the relationship to form a
■ Men should be attracted to women who
new one with potential rivals)
are likely to be able to reproduce
Social Behaviour: Actions that affect not just the individuals
soon/more often than other females +
performing them, but other individuals as well
should desire a greater number of mates
(prefer younger woman + casual sex + ● One question that doesn’t seem to make sense in light of
more sexual partners) natural selection is: Why do people help others?
■ Conversely, women should be attracted ○ Ex: Eusocial insects (ie. ants, termites, some bee
to men who are likely to invest in their and wasp species) all have a radical reproductive
offspring + should desire fewer mates division of labour meaning that a minority of
(prefer wealthier, slightly older men) individuals reproduce, and the rest are sterile and
help to defend the colony and rear the young

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