PSY318 Evolutionary perspectives on romantic and sexual relationships
Lecture 1
We're looking at evolutionary theory across:
• Mate preferences
• Mate choice
• Relationship formation
• Relationship functioning
• Relationship dissolution
Sexual orientation – downfall of evolutionary psychology... we still don’t have a good theory for why
homosexuality exists within evolutionary psychology, it is mainly focused on heterosexual ones. Partly
because results can be boring – upon doing some sex difference research comparing men and women
for mate preference for example, you’ll find the same results, just the target of affections has changed,
that’s all. Homosexuals aren’t different to heterosexuals.
Cross-cultural research – big in evolutionary psychology, as we’re trying to make conclusions about
humans everywhere not just humans from a certain culture.
Importance of evolutionary perspectives:
• Blank slate perspective in psychology can't explain everything (not all learned from others, lots
of things innate and instinctual)
• Not nature vs nurture, but an interaction perspective
• Most people agree our bodies have evolved from ancestors-->humans. There is more
controversy surrounding what has happened with our brains.
, • Cranial capacity had drastic increase in last 2 billion years (frontal lobes etc. expanding)
• If the brain has evolved, its going to be in this time, when its growing at such a pace
• We can look at what life was like for our ancestors during this time, to look into the threats &
benefits they needed to evolve their psychology in line with.
General evolutionary theories:
Evolution: “the process by which new species or populations of living things develop from preexisting
forms through successive generations” - Merriam-Webster
--> Natural selection historical background
• A scientific theory of evolution, a change in heritable characteristics over time
• Coined by Charles Darwin in 1859 (he didn’t know much about genes at the time)
• Even with no genes to look at, it's no problem, as his work with comparative anatomy,
embryology, fossil evidence, geographic location etc., helped build a strong picture for NS.
Darwin collected a vast amount of evidence.
• Not the only theory of evolution (Lamarckian – whatever happens to the parent gets passed
onto the child, another theory developed in the absence of genes)
• Also documented by Alfred Wallace, and many others.
• Some vest sexual selection under NS, others think it’s its own separate volition.
,Artificial selection
• Human doing AS is making the choice- ‘I want to push a species that way, I want it to be
bigger/stronger etc.’
• It is intuitive, as we can see it around us (e.g., a dog that comes from 2 different breeds looks
like a mix of the 2 breeds)
• AS is a case of filtering; you have a population, you select the ones which have the qualities you
want more of and breed these more until you have a population with the desired qualities.
• e.g., proto banana-->modern banana in 7,000 years, we still have both ‘breeds’ today
Natural selection
• The environment is selecting
• Some animals best fitted to current environment than others – these thrive, strive & reproduce,
so in the next gen, they represent more of the leftover stock who can then carry on the lineage
of that species.
• NS provides a filter; could be survivability in terms of avoiding predation, access to food, being
able to reproduce
• e.g., Darwin found on the Galapagos islands, finches native to each island that looked very
similar apart from their beaks. He surmised a relationship between their beaks & the food
sources on the island. He concluded that an initial prototypical finch became more specialized
versions through NS: ancestor finch--> insect-eating (short, narrow beak)/ woodpecker type
insect-eating (large, long beak)/ seed-eating (short stubby beak) [Grant & Grant (2003)]
• Lots of adaptations can add up to big qualitative changes over big lengths of time
• e.g., we're pretty sure a lang based mammal became committed to the sea as a whale, shown
by fossils.
• In NS evolution, body parts etc. that aren't being used anymore don’t get removed, but instead
get riddled with mutations and hang out for a while.
• Ironically, the human brain wasn't evolved to be able to fathom these big time scales of
millions/billions of years.
Sexual selection
• Other organisms are selecting each other.
• Some say this is a form of NS
• Others raise it as a form of selection in its own right, as it’s so powerful.
• More barriers to reproduction than survival
• Competition within the same sex – intra-sexual selection
• Competition between two sexes – inter-sexual selection
• Sexual selection boils down to variance in reproductive success due to pressures from within the
species related to reproduction (e.g., same-sex competitors, opposite-sex choice)
• More genes are passed onto next generation if one can
-fend off competitors for sexual access
, -increase the rate of reproduction
-increase the quality of one’s offspring (mate better)
• If a human is deciding to only mate with another human who meets the criteria of a certain
filter, then that filter is an element of ‘artificial’ selection, except not every human is on the
same page with what their filter is.
• Sexual selection occurs across all species that reproduce sexually, whereas AS is uniquely a
human thing.
• Uneven selection pressures where one sex has more than the other – e.g., ornaments for
attraction such as peacock's tail, also you have weapons for competitiveness with the same sex,
such as elephant seals being larger – these ornaments/weapons are often sexually dimorphic
(pertains to one sex and not the other, uneven selection pressure on one sex and not the other,
get this more so in species that are more polygamous/promiscuous)
• Every now and then, you get monogamous species where the selection pressure is equal –
males and females will have very similar adaptations and look/act almost the same way. E.g.,
gibbons – we are very much like them in terms of m/f not having much aesthetic difference.
They both sing to keep competitors away from their mate (a sexually selected
weapon/ornament)
• In humans, the biggest sexually selected thing that we have is our brain – what it can show off,
etc. Things like art, creativity, singing, dancing are ways of showing off how high quality our
brains are (superfluous things that aren’t required for survival). [Jeffrey miller’s ‘mating mind’]
Selection constraints
• Evolution just works with whatever you currently have, nudging it, generation by generation in a
certain direction
• In whales, you can still find every single bone that the human hand has, and the same in a bat’s
wing.
• Growing, extending & adding, but always must be in a forward direction, no going back (e.g.,
giraffe’s neck)
• 3 things you need for selection to take place – variation in a trait (with relation to genetic code),
heredity & selection
The units of selection
• Selection acts at the level of the organism; more specifically the genes within that organism (not
the species as a whole- evolution doesn’t work at the group level)
• E.g., lemmings throwing themselves off cliffs – rumor that some lemmings would willingly end
their own life for the good of the species, due to food shortages. This was a lie, documentaries
made on this were falsified. Doesn’t make any sense, as if a single lemming decided not to do
that, then it would be one of the ones left behind to reproduce. Providing that selfishness is
linked to its genetic code somehow, and then also its offspring, then there would be more of
them than those who were suicidal, which apparently there aren’t. Very quickly, a level of
Lecture 1
We're looking at evolutionary theory across:
• Mate preferences
• Mate choice
• Relationship formation
• Relationship functioning
• Relationship dissolution
Sexual orientation – downfall of evolutionary psychology... we still don’t have a good theory for why
homosexuality exists within evolutionary psychology, it is mainly focused on heterosexual ones. Partly
because results can be boring – upon doing some sex difference research comparing men and women
for mate preference for example, you’ll find the same results, just the target of affections has changed,
that’s all. Homosexuals aren’t different to heterosexuals.
Cross-cultural research – big in evolutionary psychology, as we’re trying to make conclusions about
humans everywhere not just humans from a certain culture.
Importance of evolutionary perspectives:
• Blank slate perspective in psychology can't explain everything (not all learned from others, lots
of things innate and instinctual)
• Not nature vs nurture, but an interaction perspective
• Most people agree our bodies have evolved from ancestors-->humans. There is more
controversy surrounding what has happened with our brains.
, • Cranial capacity had drastic increase in last 2 billion years (frontal lobes etc. expanding)
• If the brain has evolved, its going to be in this time, when its growing at such a pace
• We can look at what life was like for our ancestors during this time, to look into the threats &
benefits they needed to evolve their psychology in line with.
General evolutionary theories:
Evolution: “the process by which new species or populations of living things develop from preexisting
forms through successive generations” - Merriam-Webster
--> Natural selection historical background
• A scientific theory of evolution, a change in heritable characteristics over time
• Coined by Charles Darwin in 1859 (he didn’t know much about genes at the time)
• Even with no genes to look at, it's no problem, as his work with comparative anatomy,
embryology, fossil evidence, geographic location etc., helped build a strong picture for NS.
Darwin collected a vast amount of evidence.
• Not the only theory of evolution (Lamarckian – whatever happens to the parent gets passed
onto the child, another theory developed in the absence of genes)
• Also documented by Alfred Wallace, and many others.
• Some vest sexual selection under NS, others think it’s its own separate volition.
,Artificial selection
• Human doing AS is making the choice- ‘I want to push a species that way, I want it to be
bigger/stronger etc.’
• It is intuitive, as we can see it around us (e.g., a dog that comes from 2 different breeds looks
like a mix of the 2 breeds)
• AS is a case of filtering; you have a population, you select the ones which have the qualities you
want more of and breed these more until you have a population with the desired qualities.
• e.g., proto banana-->modern banana in 7,000 years, we still have both ‘breeds’ today
Natural selection
• The environment is selecting
• Some animals best fitted to current environment than others – these thrive, strive & reproduce,
so in the next gen, they represent more of the leftover stock who can then carry on the lineage
of that species.
• NS provides a filter; could be survivability in terms of avoiding predation, access to food, being
able to reproduce
• e.g., Darwin found on the Galapagos islands, finches native to each island that looked very
similar apart from their beaks. He surmised a relationship between their beaks & the food
sources on the island. He concluded that an initial prototypical finch became more specialized
versions through NS: ancestor finch--> insect-eating (short, narrow beak)/ woodpecker type
insect-eating (large, long beak)/ seed-eating (short stubby beak) [Grant & Grant (2003)]
• Lots of adaptations can add up to big qualitative changes over big lengths of time
• e.g., we're pretty sure a lang based mammal became committed to the sea as a whale, shown
by fossils.
• In NS evolution, body parts etc. that aren't being used anymore don’t get removed, but instead
get riddled with mutations and hang out for a while.
• Ironically, the human brain wasn't evolved to be able to fathom these big time scales of
millions/billions of years.
Sexual selection
• Other organisms are selecting each other.
• Some say this is a form of NS
• Others raise it as a form of selection in its own right, as it’s so powerful.
• More barriers to reproduction than survival
• Competition within the same sex – intra-sexual selection
• Competition between two sexes – inter-sexual selection
• Sexual selection boils down to variance in reproductive success due to pressures from within the
species related to reproduction (e.g., same-sex competitors, opposite-sex choice)
• More genes are passed onto next generation if one can
-fend off competitors for sexual access
, -increase the rate of reproduction
-increase the quality of one’s offspring (mate better)
• If a human is deciding to only mate with another human who meets the criteria of a certain
filter, then that filter is an element of ‘artificial’ selection, except not every human is on the
same page with what their filter is.
• Sexual selection occurs across all species that reproduce sexually, whereas AS is uniquely a
human thing.
• Uneven selection pressures where one sex has more than the other – e.g., ornaments for
attraction such as peacock's tail, also you have weapons for competitiveness with the same sex,
such as elephant seals being larger – these ornaments/weapons are often sexually dimorphic
(pertains to one sex and not the other, uneven selection pressure on one sex and not the other,
get this more so in species that are more polygamous/promiscuous)
• Every now and then, you get monogamous species where the selection pressure is equal –
males and females will have very similar adaptations and look/act almost the same way. E.g.,
gibbons – we are very much like them in terms of m/f not having much aesthetic difference.
They both sing to keep competitors away from their mate (a sexually selected
weapon/ornament)
• In humans, the biggest sexually selected thing that we have is our brain – what it can show off,
etc. Things like art, creativity, singing, dancing are ways of showing off how high quality our
brains are (superfluous things that aren’t required for survival). [Jeffrey miller’s ‘mating mind’]
Selection constraints
• Evolution just works with whatever you currently have, nudging it, generation by generation in a
certain direction
• In whales, you can still find every single bone that the human hand has, and the same in a bat’s
wing.
• Growing, extending & adding, but always must be in a forward direction, no going back (e.g.,
giraffe’s neck)
• 3 things you need for selection to take place – variation in a trait (with relation to genetic code),
heredity & selection
The units of selection
• Selection acts at the level of the organism; more specifically the genes within that organism (not
the species as a whole- evolution doesn’t work at the group level)
• E.g., lemmings throwing themselves off cliffs – rumor that some lemmings would willingly end
their own life for the good of the species, due to food shortages. This was a lie, documentaries
made on this were falsified. Doesn’t make any sense, as if a single lemming decided not to do
that, then it would be one of the ones left behind to reproduce. Providing that selfishness is
linked to its genetic code somehow, and then also its offspring, then there would be more of
them than those who were suicidal, which apparently there aren’t. Very quickly, a level of
