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Lecture

PSYCH 1XX3 Lecture Notes - Medium Ground Finch, Blue Ocean Strategy, Daphne Major


Department
Psychology
Course Code
PSYCH 1XX3
Professor
Joe Kim

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Lectures 3/4: Evolution
Introduction to Adaptations
Adaptations are biological traits or characteristics that help an individual survive and
reproduce in its habitat
Can be physical or psychological
Adaptations perform specific functions that make an organism better suited to its
environment
Adaptations are always “for” something; they serve identifiable functions in the life of
the individual
Adaptations emerge in development as a result of the activation of relevant genes in
interaction with relevant aspects of the environment
Scientists categorized as “adaptationists” look for processes that are capable of
accomplishing tasks of detecting stimuli
o In other words, they look for the relevant adaptations
o Scientists describe how hypotheses about adaptive functions guide their
investigations
Cognitive psychologists study things like selective attention, memory encoding and
retrieval and word recognition
o The very names of these tasks refer to tasks that the mind needs to accomplish
to do its job
o They refer to the adaptive functions of mental activity
o Therefore, cognitive psychologists are also adaptationists
Evolution By Natural Selection
Natural selection is one of four basic mechanisms of evolution, the others being
mutation, genetic drift and migration
The process of natural selection can be described as the differential survival and
reproduction of organisms as a result of the heritable differences between them
Three essential components to Darwin and Wallace’s insight
o First is that there are significant individual differences
Within any population, there is variation among individuals for any given
characteristic
o Second, these differences affect individuals chances of surviving and reproducing,
causing differential reproduction
Some individuals will have more offspring than others
o Lastly, the traits that give rise to differential reproduction have a genetic basis,
meaning they are heritable
The offspring of successful reproducers will resemble their parents with
respect to these variable characteristics
Ex. Imagine a population of fish that vary in colour
o Some individuals are blue and others are red

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o The blue fish camouflage well in the blue ocean water and the red fish are much
more visible to predators
o Therefore, the red fish get eaten more often and so on average, the blue fish
survive and reproduce better than the red fish
o Blue fish tend to have blue coloured offspring because body colour is a heritable
trait
o Over successive generations, there will be selective transmission of heritable
parental traits and the population will be mostly blue
o This is because the specific characteristics that are best adapted for survival and
reproduction are going to be reproduced at higher rates
o Eventually, if this process continues, the entire fish population will be blue
Natural Selection In the Wild
What researchers usually observe in wild populations is stabilizing selection, selection
against any sort of departure from the species-typical adaptive design
o This sort of selection tends to keep traits stable over generations
Ex. Blue would remain the most common colour in the fish population because it is
adaptive and minimizes the risk of predation
However, in some cases, especially when there has been a significant change in the
environment, selection favours traits that are not typical and evolutionary change can
be observed
A classic example of rapid evolutionary change comes from work on the evolution of
beak shape and size in a particular species of Darwin’s finches, the medium ground finch,
which lives on Daphne Island in the Galapagos
Peter and Rosemary Grant who studied these birds, were able to observe natural
selection within only a generation
In 1977, a drought hit the island and decimated the vegetation
o Food was scarce and all of the small seeds were quickly eaten up, leaving only
large, tough seeds that the finches usually didn’t bother with
o The birds that had unusually big, heavy beaks were able to eat the hard seeds
that remained and so survived the drought, whereas the birds with small beaks
died of starvation
o Between 1976 and 1978, the average beak depth increased
o The large-beaked survivors went on to reproduce when conditions were again
favourable for breeding and because beak size is heritable, their offspring
inherited large beaks as well
Reproductive Success Fitness
Natural selection favours those individuals who are not only best at surviving, but also
those who are best at reproducing
Fitness in biology refers to how good a particular genotype is at leaving copies of its
gene in the next generation relative to other genotypes
Therefore, the fittest individual is not always the smartest, biggest or fastest

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Darwinian fitness is the average reproductive success of a genotype relative to
alternative genotypes
Because fitness is ultimately about the competition between genotypes to leave copies
of themselves in the next generation, some evolutionary biologists like to define
evolution as a change in gene frequencies over generations
Sexual Selection
In sexually reproducing organisms there is often competition for mates and natural
selection acts on mate-finding and reproductive behaviours
o Known as sexual selection
o The component of natural selection that acts on traits that influence an
organism’s ability to obtain mates
Peacock’s tail
o Energetically expensive to produce
o Makes male more conspicuous to predators and it actually interferes with his
ability to escape from a predator
o A peacock’s tail is no help at all with respect to physical survival
o Increases the risk of dying and for that reason, he’ll shed his tail at the end of the
breeding season and grow a whole new one next year
o However, the tail contributes to a male’s fitness by increasing his chances of
mating
Traits like these that led Darwin to propose a second theory, the theory of sexual
selection
Some evolved traits like the tail elevate mortality and are actually being selected against,
but they can still evolve and become more elaborate under the countervailing pressure
of sexual selection
Stag’s antlers
o Only males have antlers and carry them around to fight for females
o In some ways, the stags are more vulnerable than the females
o Because of their bulk, males don’t have as much stamina as females for running
away from predatory wolves and a stag is more likely to get stuck in deep snow
o The total effect on survival for all his weaponry is negative
o In fact, like the peacock’s tail, stags shed their antlers at the end of the breeding
season and grow new ones each year
In both examples
o The male trait has a negative effect on survival, but has evolved and persists
anyways because it has a big positive effect on the male’s chance of mating
o An important difference between these two examples of sexually selected traits
Peacock’s don’t use their tails to fight with
Antlers have evolved to be effective weapons in fights with other males,
but the peacock’s tail evolved solely to dazzle the females
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