Theme 1
Brain Basics
Breedlove & Watson (2017): Chapter 6: Evolution of the brain and behaviour
How Did the Enormous Variety of Species Arise on Earth?
Naturalist: A student of the forms and classification of organisms. Evolution happens via
natural selection and sexual selection.
Evolution by natural selection:
1. Reproduction will tend to increase a population rapidly unless factors limit it
2. Individuals of a given species are not identical
3. Some of the variation among individuals is inherited
4. Not all the offspring of a given generation survive to reproduce
Adaptations: traits that increase the probability of successful reproduction
Convergent evolution: behavioural or structural similarities among animals that are only
distantly related in response to ecological features
- Homoplasy: a resemblance between physical or behavioural characteristics that is due
to convergent evolution
- Homology: a resemblance based on common ancestry, such as the similarities in
forelimb structures of mammals
- Analogy: similar function although the structures may look different
However, Darwin's theory didn’t sufficiently explain two mechanisms:
1. the mechanism by which an individual inherits its characteristics from its parents, and
2. the source of individual variation upon which natural selection acts
→ these were later able to be studied via genetics and mutations
Mutations occur randomly, spontaneously, are heritable, and can be good, bad, or neutral.
,Linnaeus's animal classification system: each species is assigned two names - the first name
identifying the genus, the second name indicating the species (e.g., Homo sapiens).
Order of categories, from most broad to most narrow: kingdom, phylum, class, order, family,
genus, species
Phylogeny: the evolutionary history of a group of organisms
Ecological niches: specific sets of environmental opportunities (e.g. ability to learn)
Linear descent: the idea that evolution had proceeded along a single trajectory from simple to
complex, culminating in humans
Why study particular species?
1. Outstanding features
2. Convenience
3. Comparison
4. Preservation
5. Economic importance
6. Treatment of disease
Researchers have found that the strategies that different species use to obtain food are
correlated with brain size and structure.
Vertebrate Brains
The various orders of mammals all share the same basic set of brain regions devoted to visual,
auditory, and somatosensory processing. The regions are also arranged in the same basic
pattern. However, they differ in size, proportions,
and anatomical locations following adaptation to
ecological niches.
,Vertebrate nervous systems share many characteristics:
- Development from a hollow dorsal neural tube → the head of the embryonic neural tube
goes on to form the major subdivisions of the brain, but a fluid series of hollow spaces
within the brain -the ventricular system- persists into adulthood
- Bilateral symmetry → the cerebral hemispheres are almost mirror images
- Segmentation → pairs of spinal nerves extend from each level of the spinal cord
- Hierarchical control → the cerebral hemispheres control or modulate the activity of the
spinal cord
- Separate systems → the CNS is clearly separate from the peripheral NS
- Localisation of function → certain functions are controlled by certain locations in the
CNS
Endocast: a cast of the cranial cavity of a skull, useful for studying fossils of extinct species
All mammals have a six-layered neocortex which
accounts for more than half of the brain’s volume. In
mammals the cortex is mainly responsible for
higher-order functions. Larger brains evolved by
prolonging the later stages of development
Encephalisation factor (k): a measure of brain size
relative to body size (regression line represents
WBRAIN / WBODY(0.69))
Factors That Led to the Rapid Evolution of a Large Cortex in Primates
Social brain hypothesis: suggests that a larger cortex is needed to handle the complex cognitive
task of maintaining social relationships with other large-brained individuals. Based on the
correlation between social group size and brain size, it is possible to estimate the maximum size
of various species' social groups from the size of the cortex. For humans, this value is about 150.
An alternative hypothesis about brain size states that three factors account for the enhanced
size of primate brains: (1) innovations in behaviour, (2) use of tools, and (3) social learning
Miller’s hypothesis: creativity and related brain growth is due to sexual selection for abilities to
attract attention, stimulate, and surprise a potential mate
, Humans and their closest relatives can differ on a genetic basis in two principle ways:
1. the DNA sequences of specific genes may vary in important ways between the species
2. humans and their nonhuman relatives may also differ in how those genes are expressed
to construct a complex brain
Are Humans Still Evolving?
We are living in a world in which cultural and medical developments have radically altered two
main ingredients of evolution: life span and fertility
Artificial selection: when selection is driven by human behaviour
To determine whether a candidate gene has been under strong natural selection pressure in the
recent past, scientists look at and individual’s haplotype: how the gene is bundled together with
its neighbouring stretches of DNA
Single-nucleotide polymorphisms (SNPs): minor variations where one nucleotide substitutes
for another can occur within a gene. Most SNPs have just two different versions (alleles). If one
particular allele confers a slight reproductive advantage on those who possess it, it will come
under natural selection pressure-it will be "selected for"
Breedlove & Watson (2013): Chapter 2: Functional Neuroanatomy
The Nervous System
The neuron doctrine: proposes that (1) the brain is composed of separate neurons and other
cells that are independent structurally, metabolically, and functionally; and (2) information is
transmitted from cell to cell across tiny gaps (a.k.a., synapses)
Structural Divisions of the Neuron
- Mitochondrion: produces energy
- Nucleus: contains genetic info
- Ribosomes: translate genetic info into proteins
