PSYC 2410 – Chapter 2
Most people now understand that human behaviour has a physiological basis, but many still cling to the dualistic
assumption that there is a category of human activity that somehow transcends the human brain.
Ethology – the study of animal behaviour in the wild
Asomatognosia – a deficiency in the awareness of parts of one’s own body. Usually involves the left side of the body and
usually results from damage to the right parietal lobe.
Evolution: WHY questions
Mechanisms: HOW questions
Ex: Why do all humans show the same kind of facial expression to communicate their different emotions? How do facial expressions,
such as smiling, develop? What parts of the brain are involved in the production and recognition of smiling?
Face Recognition Neurons, Mirror Neurons are the basis of imitation. Your mirror neurons fire when you are
watching someone do something, when you are imitating someone else and when someone else is imitating you.
Evolution: the change across generations. Evidence includes fossils, similarities and yet difference found in different
species, and the results of human processes of artificial selection (cats, dogs, etc.) Ex:
Before the industrial revolution, peppered moths were mostly in the white form, after the industrial revolution
they were mostly found in the black form. Might be because lichens etc. on trees darkened, so white form was
easier prey, and all the white were eaten so it became a less frequent allele in peppered moth population.
Darwin’s Finches: after the 1997 summer of severe drought, only the plants that produced large seeds survived, so
that’s all there was to eat. Finches with small beaks died of starvation, but those with big beaks could eat large
seeds and survived, thus large beaks became the more frequent allele. See cycles of beak sizes in Darwin Finch
Worked on Theories of Evolution:
Greek philosopher Anaximander (611-547 B.C.)
Greek philosopher Aristotle (384-322 B.C.)
Roman philosopher Lucretius (99-55 B.C.)
Scientist, Leonardo da Vinci (1452-1519)
Physicist, Galileo Galilei (1564-642)
Geologist, James Hutton (1726-1797)
Geologist, Charles Lyell (1797-1875)
Evolution in the 1700s
Georges-Louis Leclerc, Comte de Buffon (1707-1788): Historie Naturelle – explanation of why “species change”:
the environment acts directly on organisms through “organic particles”
Erasmus Darwin (1731-1802), Grandfather of Charles Darwin: Zoonomia, or, The Laws of Organic Life – also
thought “species changed”; Position was similar to Lamark’s and theorized about competition and sexual selection
Evolution in the 1800s
Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck (1744-1829): in 1809 Philosophie Zoologique
First comprehensive theory of Evolution: use and disuse leads to change, movement toward perfection,
changes in form through conscious will, environmental effects on organ development, inheritance of
Charles Robert Darwin (1809-1882): provided biology with great unifying principle “Theory of Natural Selection”
Based on fossils in Patagonia and the diversity of life in the Galapagos Islands (giant tortoises and finches)
Alfred Russel Wallace (1823-1913): sent a letter to Darwin in 1858 as he had a similar set of ideas.
On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural
means of Selection. By CHARLES DARWIN and ALFRED WALLACE. Journal of the Proceedings of the Linnean
Society, Zoology 3: 45-62. 20 Aug 1858.
First observation: organisms have an enormous capacity to overproduce
Second observation: populations (with a few exceptions) remain remarkably stable
o Deduction 1: there is a struggle for survival
Third observation: individuals differ in their characteristics, and many of these differences are heritable
o Deduction 2: those individuals who possess adaptive characteristics will reproduce more
successfully than those who don’t and will pass on these characteristics to their offspring. PSYC 2410 – Chapter 2
“adaptive characteristics” = Natural Selection
o Evolution is the accumulation of the changes in the population due to natural selection.
Neo Darwinism (1900s): Darwin’s theory + HEREDITY + GENETICS
Fitness: the ability of an organism to survive and to contribute its genes to the next generation
Key Points on Evolution
Similarity among species do not necessarily mean that the species have common evolutionary origins.
Homologous Structures: structures that are similar but do not have a common evolutionary origin ( arm
and bird wing) “homo” = the same
Analogous Structures: structures that are similar but do not have a common evolutionary origin (bird and
insect wings) “ana” = similar. Similarities between analogous structures result from convergent evolution,
the evolution in unrelated species of similar solutions to the same environmental demands.
It does not progress to preordained perfection
Very slow or with sudden changes
Spandrels (evolutionary by-products: belly button) that are non-adaptive
Exaptations: evolved to perform one function and were later co-opted to perform anther. Feathers evolved as
thermal insulators but, allowed potential to fly
Noise: different molecules with identical function
450 Million Years Ago:
CHORDATES: animals with dorsal nerve cords
VERTEBRATES: 425 million years ago, first animals with vertebrae (spinal bones) to protect dorsal nerves
AMPHIBIANS: 400 million years ago, bony fish ventured out of water, natural selection lead to amphibians
oREPTILES: 300 million years ago, evolved from a branch of amphibians. First vertebrates to lay shell-covered
eggs and to be covered by dry scales
MAMMALS: 180 million years ago, first time to feed offspring with mammary glands
VARIOUS HOMO SPECIES
HOMO SAPIENS 40 000 years ago
Human Evolution – The Brain
Early Homo species: 850g
Homo sapiens: 1350g
Great variability in brain size within our species, no relation of size with intelligence. Brain size intelligence
3 important points about the evolution of the human brain:
1) It has increased in size during evolution
2) Most of the increase in size has occurred in the cerebrum
3) An increase in the number of convolutions has greatly increased the volume of the cerebral cortex.
Can look at size of certain brain structures. Humans have a larger cerebrum than other animals. In fish their brain
stem is much larger than their cerebrum, in rats they are roughly equal, in cats, the cerebrum is larger than the
brain stem, and in chimpanzees it is significantly larger.
Cerebrum: complex processes (ex: learning)
Brain Stem: basic processes (ex: respiration)
Evolutionary Psychology: Understanding Mate Bonding:
Evolutionary psychologists try to understand human behaviours through a consideration of the pressures that led
to their evolution.
Most mammals tend to form mating bonds: why?
Trivers (1972) – attributes it to the fact that female mammals give birth to relatively small numbers of
helpless, slow-developing young. It is adaptive for the males to stay with the females to promote the
successful development of those offspring. PSYC 2410 – Chapter 2
Polygyny is the most prevalent pattern of mate bonding: an arrangement in which one male forms mating
bonds with more than one female. Polygyny evolved as the predominant pattern of mate bonding
because female mammals make a far greater contribution to the rearing of their young than do males.
Polyandry: mating arrangement in which one female forms mating bonds with more than one male. It
does not occur in mammals, only in species which the contributions of the males are greater than those of
the females. Ex: seahorse, male carries eggs in pouch :3
Monogamy: mate-bonding pattern in which enduring bonds are formed between one male and one
female. It is thought o have evolved in those mammalian species in which each female could raise more
young, or more fit young, if she had undivided help.
Evolution and Behaviour
Behaviour is under the control of Natural Selection
Fitness: in the Darwinian sense, is the ability of an organism to survive and contribute its genes to the next
Adaptive Behaviour is maintained
Maladaptive Behaviour is not
Find and ingest food
Self and offspring defense
Social behaviour: Aggression – Affiliation
Evolution and Social Behaviour
Social Living is Adaptive evolution
can work together, can defend better, better survival rate, many sets of eyes can locate sources of food
better than one
also depends on the environment
Social Dominance: access to resources
Establish hierarchy which becomes an important factor in determined who’s successful and who isn’t and
whose genes are passed down to the next generations
Mating Bonds: adaptive, when the members of a reproductive pair develop bonds and prefer to stay together,
when it is hard to provide proper parental care and when one parent alone can’t raise the children successfully. Ex:
Courtship Display: mate choices – may even cause speciation. Trying to choose a good parent for the offspring
with good traits. Usually female invests more and is thus choosier of which male she accepts. Males can compete
with courtship displays. Females choose which traits are passed on, can cause speciation.
Speciation: the origin of a new species/the formation of a new species
o Geographic barriers
o Behavioural barriers (courtship displays)
Species: a group of organisms that are reproductively isolated from other organisms
Conspecifics: members of the same species
Evolution of Non-Adaptive Behaviour?
Can behaviours that put an individual’s life at risk evolve? Ex: Altruism, Heroism
Altruism: behavioural acts that may actually reduce an individual’s chance of survival and interfere with
its own reproductive success.
The cost of Parental Care ex: broken-wing display. Parental care increases an individual’s fitness (pass on genes).
Broken wing display – parent pretends their wing is broken and can’t fly and hop away from the nest to
distract predator and bring them away from the next, then they fly away.
Not all behaviour will directly increase individual fitness:
Alarm calls in ground squirrels (they are often stalked and eaten by predators) but protect the others
Genes that promote altruism within an individual could become more common in subsequent generations by
increasing the survival and/or reproductive capacity of relatives who share the same genes – one’s kin.
Is it possible for altruistic behaviour to occur among unrelated individuals?
o Alliances between male baboons: they alternate in engaging an alpha male in a fight while the
other copulates with the alpha males’ female. Each take turns. PSYC 2410 – Chapter 2
o Engaging the alpha male comes with a risk. They need to survive the fight with the alpha male,
and they need to take turns so that it’s altruistic.
o Feeding in vampire bats (Desmodus rotundus). Common in south America. Feed from large
herbivores, cattle. They drink so much blood they can’t fly back, they have to crawl back to the
nest. They have high metabolism and if a bat fails to find blood, they won’t make it to the next
day. If they can’t find food, other bats will regurgitate blood for those bats. Usually to bats who
have been altruistic to them, instead of one who has not.
Reciprocal altruism will emerge more often in species where there is:
o Individual recognition: know who has been altruistic
o Long-lived individuals: need to live long enough to have past experiences
o Stable communities: same people are there over and over
o Well-developed memory: need to remember who was altruistic before
Introduction to Genetics
Darwin’s “The Origin of Species” 1859
Dichotomous Traits: traits that occur in one form or the other, never in combination
True Breeding Lines: homozygous for a trait, always produce offspring with the same trait
Gene: part of DNA that codes for the protein for colour of seed, etc.
Allele: different versions of genes, ex: A and a (brown and white)
Brown crossed with white produces F1 = all brown, then cross F1 X F1 = F2 = ¾ brown and ¼ white (recessive)
Genotype: genetic makeup
Phenotype: observable trait
Behaviour is part of the phenotype and is mediated in part by genotype.
A Very Modern Application of Mendel’s Law: the maintenance and reproduction of lines of gene knockout mice where the
non-functional gene is necessary for reproduction.
o Mated mice that carried one allele of the knockout gene and one allele of the wild type. Dihybrid Cross which
produced ¼ homozygous wildtype, ½ hetero wildtype – knockout and ¼ homozygous knockout.
Genes are segments of DNA on Chromosomes: DNA found in the nucleus as chromosomes for most of cell life
Chromatin = DNA + Histones and other nuclear proteins
Genes – Chromosomes and Reproduction
o Chromosome pairs: maternal/paternal
o Pair Number: species-specific
o Humans: 23 pairs (46 total)
o Pair 23: X and Y sex chromosomes
o Fertilization: 2 gametes 1 zygote
Gametogenesis through Meiosis
o Start with 23 pairs of 46 chromosomes
o Replication occurs before Prophase 1: 23 pairs of 46 chromosomes, 23 tetrades
o First division: each daughter cell has 23 chromosomes, with two sister-chromatids
o Second division: each daughter cell has 23 chromosomes, only one chromatid
o Oogenesis produces one Ovum
o Spermatogenesis produces four sperm cells
o Sperm fertilizes the ovum, and it now has 23 pairs of 46 chromosomes.
o The newly formed Zygote then reproduces mitotically.
There’s more to Variability: Thomas Hunt Morgan (1866-1945)
o Crossing-Over occurs to increase genetic variability, only occurs between non-sister chromatids in a tetrad.
Produces four different chromatids.
o Gene Linkage: depends on distance of map units between different genes. Some genes are more likely than others
to occur together. Ex: blond hair and blue eyes PSYC 2410 – Chapter 2
Structure of DNA
o Discovered by Watson and Crick in 1953, the original paper was only one page with two columns. Became
immediately apparent that their discovery was crucial
o 1962 Nobel Prize in Medicine
o Double Stranded Helix
Each stand: a sequence of nucleotide bases connected by Phosphate and Deoxyribose
4 bases: adenine, thymine, guanine and cytosine. A-T, C-G complimentary.
Parent DNA unzips, then complementary bases fit in place to create two separate DNA helixes
o Structural Genes (most genes): gene encodes proteins (amino acid sequences)
o Operator genes (switches): control one or more structural genes
o Enhancers: stretches of DNA whose function is to determine whether particular structural genes initiate the
synthesis of proteins and at what rate.