1. Brain Regions in Seven Classes of Vertebrates
The main brain structures are the same in all vertebrates
Details not on the exam
The main brain structures are the same in all mammals (and other vertebrates.
The relative sizes, proportions, and anatomical locations of these brain structures have been subject to evolutionary modification as the species have adapted to their unique ecological niches.
The Evolution of Vertebrate Brains Reflects Changes in Behavior
One important adaptation is the ability to learn, in order to find food and to avoid danger
Differences in brain size and structure can be due to behavioral adaptations.
Novel or strategic food-seeking behavior is correlated with larger brain size.
Animals who depend on hearing, vision, or memory for their food develop larger related brain structures
Mammals’ lifestyles are related to cortical organization:
Many Factors Led to the Rapid Evolution of a Large Cortex in Primates
Nocturnal rats that use whiskers have a large part of their cortex devoted to their whiskers, but only a little to vision.
The platypus uses its bill to detect mechanical and electrical stimuli – most of its somatosensory cortex is devoted to the bill.
Should focus on specialized brain structures not brain size
So Animals dependent on specialized hearing, vision, or memory for their food have evolved larger related brain structures.
Note: Optic Tectum is called Superior Colliculus in mammals, used to control eye movement and coordinate visual spatial movement

2. Figure 6.13 The Relation between Brain Weight and Body Weight
The black diagonal line is a regression line, the line of best fit
Figure The Relation between Brain Weight and Body Weight
Brain weight is related here to body weight in several mammalian species. Note that both axes are logarithmic, so the graph includes a wide range of brain weights and body weights. A polygon has been drawn to connect the extreme cases and include the whole sample. The black diagonal line is a line of best fit (also known as the regression line), indicating a prediction line for brain size among mammals as a group. For each species, the encephalization factor, k, corresponds to the distance (the residual) between the line and the brain weight value for that species. Although not shown, bird species are about as “brainy” as mammals, but reptile species are substantially less so (Jerison, 1991; H. Stephan et al., 1981).
Details not on the exam

3. Who Is the Brainiest? Details not on the exam
We must be careful not to interpret change over time, including the change in brain size, as if it were a linear evolutionary sequence.
The main classes of vertebrates represent different lines or radiations of evolution that have been proceeding separately and simultaneously for at least 200 million years.
For example, today’s sharks have much larger brains than primitive sharks had, but the evolution of large-brained sharks had nothing to do with the development of large brains in mammals.
The line of descent that eventually led to mammals had separated from the shark line long before the large-brained sharks evolved.
Through evolution, vertebrate brains have changed in both size and organization.
One difference in basic brain structure between the lamprey and other vertebrates is that the cerebellum in the lamprey is very small.
The differences are not in the basic subdivisions but in their relative size and elaboration.
All mammals have a six-layered cortex, also called neocortex.
Reptiles were the first vertebrates to have a cerebral cortex, but they have only three cortical layers, unlike the six cortical layers of mammals.
The encephalization factor is a measure of brain size relative to body size.
The relationship between brain weight and body weight is similar for all classes of vertebrates.
Brain weight relative to body size does vary between and within classes

4. Brain Region Proportions in Primates
Details not on the exam
Brain evolution shows size changes both in specific regions and overall.
Some animals have larger brains
Some brain regions “frontal cortex” are especially large
The size of each brain structure is highly correlated with the total brain size.
Most brain areas increase in size relative to whole brain
However, the rate of increase in some brain areas can differ between small and large brains.
Specialized areas for sensory input
Specialized areas for cognition
rate of increase in some brain areas can differ
Specialized areas for sensory input
Specialized areas for cognition

5. Evolution Allows Later-Developing Brain Regions to Grow Larger
Details not on the exam
Larger brains have evolved by prolonging the later stages of development.
In primates, brain regions that develop later have enlarged more than earlier regions.
Larger brains have evolved by prolonging the later stages of development.
In humans, this may explain changes in the cortex, where new neurons form the outermost layers.

6. The Metabolic Trade-off
Neural tissue is very “expensive” to maintain
Requires large numbers of calories
Every increase in the quantity of neurons will have a metabolic cost
In order for a brain to evolve in size, the organism must either:
Decrease the caloric demands of some other tissue
Evolve a way to acquire calories more efficiently
E.g., Trade-off between brain size and digestion
Brains must provide selective advantages to evolve beyond the minimum size and organization necessary for the organism’s continued success.

7. Hominid Evolution Costs of a large brain
Hominid brains enlarged rapidly in our recent evolution.
Australopithecines were hominids that made and used tools.
The ability to use tools reduced the necessity for large jaws and teeth, and those became steadily smaller.
As Homo erectus evolved, brains became larger and faces got smaller than the australopithecines.
Homo erectus made elaborate tools, used fire, and hunted. They also expanded their area over three continents.
With Homo sapiens, brain volume evolved rapidly and had reached modern levels about 150,000 years ago.
Costs of a large brain
A long gestation period
Prolonged dependence on parents
High metabolic cost
Complex genes are vulnerable to mutation
Adaptive advantages of a large brain include:
Ability for group interaction
Social brain hypothesis social learning
Positive correlation between clique size and size of the cortex
Innovative behavior
create and use tools
transmit culture
Problem solving, better able to handle a novel environment

8. Three important factors from comparing primates species
What are Big Brains For?
Three important factors from comparing primates species
Innovations in behavior
Use of tools
Social learning
Positive correlation with executive function and these factors
Ability to adapt to a novel environment or to a changing environment

9. The Social Brain Hypothesis
Specialized social cognitive brain circuits
Social brain hypothesis: role of social learning
Theory of mind is the ability to understand another individual’s mental state and take it into account in one’s own behavior
Syntactical–grammatical language is a unique human cognitive ability
Thicker cortical layer
Higher density of cortical neurons
Organized into columns

10. Figure 6.21 Transmitting Culture
Culture has been observed in nonhuman primates. For example, a population of Japanese macaques developed a set of behaviors that included washing food, playing in water, and eating marine food items, and they transmitted this culture of water-related behaviors from generation to generation.

11. Evolution of Brains Reflects Changes in Development
In primates, brain regions that develop later have enlarged more than earlier regions.
Larger brains have evolved by prolonging the later stages of development.
In humans, this may explain changes in the cortex, where new neurons form the outermost layers.
Very similar genomes can produce different brains:
A few crucial genes can have a great effect on development. 11

12. Figure 6.19 Fetal Development outside the Womb
(After Bogin, 1997.)

13. Evolution of the brain Small changes in DNA can alter the timing and location of gene expression Genes regulate the timing of development Rate of development Duration of development Shape and size of brain anatomy determined by Number of neurons Type of neurons Organization of brain circuit
Very similar genomes can produce different brains:
A few crucial genes can have a great effect on development.
Small changes in DNA can alter the timing and location of gene expression.
Evolution of the brain
Change in genes because of mutations and selection
Some genes code for proteins
Some genes regulate gene expression
Small changes in DNA can alter the timing and location of gene expression
Genes regulate the timing of development
Rate of development
Duration of development
Shape and size of brain anatomy determined by
Number of neurons
Type of neurons
Organization of brain circuits

14. Over Your Head: Normal mice have a simple cortex without sulci or gyri whereas the transgenic mouse have a much more complex folded cortex
Some evolution can be rapid:
Overuse of antibiotics speeds evolution of resistant bacteria.
Bighorn rams with smaller horns are not hunted, thereby surviving longer.
Darwin’s finches continue to change in response to food supply.
The largest cod are kept, and remaining ones mature at smaller sizes.
Evolution of the brain
Change in genes because of mutations and selection
Some genes code for proteins
Some genes regulate gene expression
A few crucial genes can have a great effect on development.
Small changes in DNA can alter the timing and location of gene expression
Genes regulate the timing of development
Rate of development
Duration of development
Shape and size of brain anatomy determined by
Number of neurons
Type of neurons
Organization of brain circuits

15. The Cutting Edge: Are Humans Still Evolving?
“… but medical science has now largely replaced natural selection in determining who dies and who gets to reproduce.” page 188 Breedlove and Watson.
Well Yes and No
What about these people ?????
Good health care has extended life span but some individuals will die before reproducing so there is still natural selection.
Can not separate genetics and experience they are integrated
Culture including medical science is a product of the human brain.
Natural selection for special brain circuits makes culture possible.
Culture is part of the environment so culture contributes to the selection process.

16. Divisions of the Human Nervous System in the Embryo and the Adult
Neural tube
develops into three subdivisions, the forebrain, midbrain and hindbrain
Forebrain later develops into the
Telencephalon (Cortex, Basal Ganglia, Limbic System)
Diencephalon (Thalamus, Hypothalamus)
Neural tube – develops into three subdivisions, the forebrain, midbrain and hindbrain
Forebrain later develops into the
Telencephalon (Cortex, Basal Ganglia, Limbic System)
Diencephalon (Thalamus, Hypothalamus)
Midbrain is called mesencephalon
Hindbrain develops into two subdivisions:
Metencephalon, which becomes the cerebellum and pons
Myelencephalon, called the medulla
Brainstem refers to the midbrain, pons, and medulla
Development follows an orderly sequence with precise timing that is unique to every species

17. Divisions of the Human Nervous System in the Embryo and the Adult

18. Cellular Differentiation
a primitive cell becomes a more specialized cell type
occurs during the development of a multicellular organism
A result of regulation in gene expression
Produces the many cell types that make up the complex system of tissues.
Sperm Entering Egg
Embryo with 8 cells
Five Day Embryo
Approximately 2.5 days

19. Development of the Nervous System in the Human Embryo and Fetus
The mature human brain has about 100 billion neurons.
The developing nervous system relies on genetic information and its environment
A zygote is a fertilized egg.
A human embryo will develop three cell layers:
Ectoderm–outer layer, becomes the nervous system
The neural groove forms between ridges of the ectoderm.
The neural tube forms from the neural ridges.
The anterior part of the neural tube has three subdivisions–the forebrain, the midbrain, and the hindbrain.
A developing human is called an embryo for the first 10 weeks, then is called a fetus.
5 weeks postnatal
See fig 6.19

20. 7 Development of the Nervous System Can Be Divided into Six Distinct Stages
Neurogenesis—mitotic production of neurons from nonneuronal cells
Cell migration—movement of cells to establish distinct populations
Differentiation—transformation of precursor cells into distinctive neurons or glial cells
Synaptogenesis—establishment of synaptic connections
Neuronal cell death—selective death of many nerve cells
Synapse rearrangement—loss or development of synapses, to refine synaptic connections

21. The Six Stages of Neural Development
Neurogenesis–mitosis produces neurons from nonneuronal cells
Cell migration–cells move to establish distinct populations
Differentiation–cells become distinctive neurons or glial cells
Synaptogenesis–establishment of synaptic connections
Neuronal cell death–selective death of some nerve cells
Synapse rearrangement–loss or development of synapses, fine-tuning

22. The Proliferation of Cellular Precursors of Neurons and Glial Cells
Neurogenesis is the production of nerve cells. Nonneural cells divide through mitosis and form the ventricular zone. Cells leave the ventricular zone and become either neurons or glial cells.
Neurogenesis is the production of nerve cells.
Nonneural cells divide through mitosis and form the ventricular zone.
Cells leave the ventricular zone and become either neurons or glial cells.

23. Glial Spokes Guide Migrating Cells
During cell migration, cells move away from the ventricular layer. Systematic movement of cells to form parts of the brain, see fig 2.15
Radial glial cells act as guides for cells to migrate along.
Cell adhesion molecules (CAMs) are proteins on cell surfaces that promote adhesion of parts of the nervous system to guide cells
During cell migration, cells move away from the ventricular layer.
Radial glial cells act as guides for cells to migrate along.
Cell adhesion molecules (CAMs) promote adhesion of parts of the nervous system to guide cells.

24. Figure 2.15 Layers of the Cerebral Cortex
(A) The six layers of cortex can be distinguished with stains that reveal all cell bodies (left) or with stains that reveal a few neurons in their entirety (right). (B) This pyramidal cell has been enlarged about 100 times.