3.6 THE BRAIN
♥︎ THEME 1: BRAIN BASICS ♥︎
Breedlove & Watson CH 6: evolution of the brain and behaviour
VARIETY OF SPECIES
● Naturalists that study forms and classification of organisms, argue that species have
similarities in structures, so they must come from a single ancestor
● There is evidence of evolution, animal species are continually changing across
generations, gradually gaining some features and losing others, and sometimes
spinning off new species while others become extinct
● Evolution of natural selection by Darwin & Wallace
○ Darwin speculated that different birds had all descended from a single
ancestral species long ago but that, isolated on various islands, they had
gradually diverged from their ancestors and from one another
○ Observations: (1) reproduction will tend to increase 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 given
generation survive to reproduce
○ Inference: variations among individuals affect the probability of their surviving
long enough to reproduce, thereby passing on their individual characteristics
to their offspring
○ New adaptations, traits that increase the probability of successful
reproduction, will eventually predominate in the population
○ Both psychological functions and organs of body are products of evolution
○ Sexual selection says that members of each sex exert selective pressures on
the other in terms of both anatomical and behavioral features that favor
reproductive success
● Convergent evolution is when adaptation to similar ecological features results in
similarities in behavior or structure among animals that are distantly related e.g. body
form of tuna and dolphin due to efficient swimming
● Homoplasy is the resemblance between physical or behavioral characteristics that is
due to convergent evolution
● Homology is a resemblance based on common ancestry e.g. forelimb structures in
mammals
● Analogy refers to similar function, although structures may look different e.g. hand of
human and trunk of elephant are analogous features
● Problems natural selection: uncertainty about mechanism by which individual inherits
its characteristics from its parents, and source of individual variation upon which
natural selection acts
● Modern evolutionary theory by Mendel combines natural selection and genetics
○ Provided laws of hereditary that formed the foundations of genetics
○ De Vries noted that occasionally a new feature arose spontaneously and was
then passed on to successive generations, evolution could proceed by sudden
jumps, or mutations
, ○ Mutations occur spontaneously and randomly, they are the result of changes
in organism’s genes so are heritable (can be harmful, neutral or beneficial)
● Chromosomes are supercoiled lengths of DNA, found within the cell nucleus, that
contain the genes that encode the tens of thousands of proteins that make up the
body
● Epigenetics is the study of factors that affect gene expression without making
changes in structure of the genes themselves
● Linnaeus proposed the basic classification system
○ Each species is assigned genus (group of species that resemble each other
due to shared inheritance) and species (group of individuals that can
interbreed to produce fertile offspring) e.g. Homo sapiens
○ Order of categories from broad to narrow: kingdom, phylum, class, order,
family, genus, species → mnemonic to help remember: kindly put clothes on,
for goodness' sake
○ Phylogeny is the evolutionary history of a particular group of organisms,
reflects similarities between species fo organisms
● The proportion of differences between DNA samples from two species can be used
as a "molecular clock" to estimate how long ago they diverged from a common
ancestor, but these are just approximations
WHY STUDY OTHER SPECIES?
● Different kinds of animals have evolved specific behaviors and neural mechanisms
that allow them to exploit specific sets of environmental opportunities, or ecological
niches
● Comparing species leads to deeper understanding because evolutionary framework
provides additional explanatory power
, ● Criteria when selecting species: outstanding features, convenience (breed fast, not
endangered, lifespan, methodological reasons), comparison (closely related but
behave differently), preservation of biodiversity (set priorities and options for
endangered species), economic importance (animals for agriculture or food, increase
production and decrease loss), treatment of disease
● One important adaptation is the ability to learn and remember, even simple animals
show these and their study can provide insights into memory mechanisms in
more-complex animals
● Size of brain regions and adaptations
○ Strategies different species use to obtain food are correlated with brain size
and structure e.g. difficult (ripe fruit) vs difficult to find (grass)
○ More innovative bird species tend to have larger forebrains
○ Bats that depend on hearing to locate prey have larger auditory center and
those relying on vision have larger visual center in superior colliculus
○ Birds that store food for later use have larger hippocampus than those that do
not store food
○ Birds that sign many songs to attract mates have larger volume of higher
vocal center (HVC) in the brain
○ Rats have small primary visual cortex because are nocturnal and do not use
vision a lot
● Many researchers study the simpler nervous system of invertebrates to understand
basic cellular mechanisms of learning and memory that are shared across species
BASIC BRAIN STRUCTURES IN VERTEBRATES
● All mammals share the same basic set of brain regions devoted to visual, auditory,
and somatosensory processing
○ Regions are arranged in the same basic pattern
○ However, sizes, proportions and anatomical locations differ as the species
adapted to their unique ecological niche
○ Similarities in structure and organization of mammalian brains reflect the
heritage of our evolution from a common ancestor long ago
