1. Evolution and the Brain
Jana Vukovic
Human Neurobiology 217
As you can imagine this is an extremely broad topic and I will focus on several aspects relating to evolution of the brain. The way to understand the history of vertebrate evolution is to first get some idea of how species of animals are categorised. Then we can trace the presumed course of evolution and see how it affected the brain.

2. Key points Classifying the human
Vertebrate vs. invertebrate nervous system
Less to more complex vertebrate nervous system
Brain size and evolution

3. Origin of Brain Cells and Brains
Despite the age of the Earth (4 500 million years), brain cells and brains are quite recent adaptations
– First forms of life: million years ago
– First brain cells: million years ago
– First brain: million years ago
– First human-like brain: million years ago
– Modern brain: million years ago

4. Classification of Life
• up to 100 million species of life on Earth
only described about 1.5%
Taxonomy:
– Branch of biology concerned with naming and
classifying species
– Groups organisms with common characteristics

5. To classify the modern human

6. Five different kingdoms:
• Monera (bacteria)
• Protista (single cells)
• Plantae (plants)
• Fungi (fungi)
• Animalia (animals)
The only ones with brain cells and brains.

7. Animal phyla
Different Phyla

8. Chordates: Invertebrate vs.vertebrate
Complexity of movement

9. – Sensory and motor neurons
• Nerve net:
– Sensory and motor neurons
Anemone

10. Segmented nerve trunk:
– Divided into a number of parts
– Bilaterally symmetrical
Ganglia:
– Collection of nerve cells that function somewhat like a brain
C. elegans
Ascidian

11. Invertebrate vs. Vertebrate Nervous System
Nerve nets, segmented nerve trunk, ganglia
Stimulus/response, receptor/effector
Reflexes, conditioned responses
Vertebrate
– Brain and spinal cord encased in cartilage/bone
Earthworm – invertebrate
– Crossed organization: Each hemisphere receives information
from and controls the opposite side of the body
– Spinal cord is dorsal at the back of the heart and gut

12. Evolution of Vertebrate Nervous System
• Behavioral complexity is correlated with the evolution of cerebral hemispheres and cerebellum:
– Cerebellum: involved in the coordination of motor and possibly other mental processes
– Increased size and folding (to fit more tissue into the skull)

13. Less to more complex vertebrates

14. Less to more complex vertebrates Cortical specilasation
Sensory/motor cortex
Frontal cortex

15. Less to more complex vertebrates
Changes in representation of the body on the
sensory cortex and locomotion

16. Less to more complex vertebrates (i.e. rat to human)
Changes in size vascularity
variety of non-neuronal cells
Complexity of circuits
Changes in time course of development
Changes in relative size of different parts of the brain
Many conservative features – eg. neurochemistry

17. Chordate – mammals – primates
Features common to primates:
• Excellent color vision
• Eyes in front of face: enhance depth perception
• Females: Usually only one infant per pregnancy;
infants require more care
• Larger brains

18. Primates hominidae • Hominid:
– Primates that walk upright; includes all forms of humans, living and extinct
• Australopithecus
– Austral: “southern”; pithekos: “ape”
– Our distant ancestor
• Gave rise to the genus Homo, or human
– 4 million years ago
Brains were 1/3 the size of ours
• Homo habilis (“handy human”)
– 2 million years ago; in Africa
– Made simple stone tools
• Homo erectus (“upright human”)
– Migrated to Europe and Asia
– 1.6 million years ago
– Larger brain than H. habilis
– More sophisticated tools than H. habilis

19. • Homo sapiens (“wise human”)
– Africa and Asia: 200,000 years ago
– Europe: 100,000 years ago
– Larger brain that H. erectus
– Coexisted with other hominids
• Example: Neanderthals, who had comparable or even larger brains than H. sapiens
• Exact reason why we replaced Neanderthals is unknown

20. Brain size in mammals

21. Encephalization Quotient
Encephalization Quotient (EQ):
– Measure of brain size obtained from the ratio of actual brain size to the expected brain size for an animal of a particular body size
• H. sapiens have the largest EQ

22. Why is the Hominid Brain Enlarged ?
1. The Primate Lifestyle
• Eating behavior of primates is more complex than other animals
– Finding fruit is more difficult than eating grass
or other vegetation on the ground
• Need good sensory, spatial, and memory skills
– Fruit eaters have larger brains

23. Why the Hominid Brain Enlarged
2. Changes in Hominid Physiology
Radiator Hypothesis (Falk, 1990)
– The more active the brain is, the more heat it generates
Increased Blood Circulation
Improved Brain Cooling
Enabled Size of Hominid Brains to Increase
Stedman and colleagues (2004)
Genetic Mutation
Smaller Facial Muscles & Bones
Change in Diet
Increased Brain Size

24. Why the Hominid Brain Enlarged
3. Neoteny
• Rate of maturation is slowed
– Allows more brain cells to be produced
• Adults retain some infant characteristics
• Newly evolved species resemble the young of their common ancestors
– Human heads look more like the heads of juvenile chimpanzees than adult chimpanzees

25. Modern Humans Are people with larger brains more intelligent?
Problems with answering this question:
How does one measure intelligence?
• How does one measure brain size?
– Control for skull thickness
– Volume versus weight
– Control for body weight
• Can fluctuate within an individual over time
– Effect of age, physical health, brain damage?

26. Modern Humans Are people with larger brains more intelligent?
• Brain size and intelligence do not seem to
be particularly related
– Research has shown that many smart people
(e.g., Einstein) have average size brains
– Women’s brains weigh about 10% less than
men, but the two sexes do not differ in measures of average intelligence

27. Can you name few differences between the invertebrate and vertebrate nervous system?
- Nerve nets, ganglia
- Stimulus/response, receptor/effector
- Reflexes, conditioned responses
Vertebrate
– Brain and spinal cord encased in cartilage/bone
– Crossed organization: Each hemisphere receives information
from and controls the opposite side of the body
– Spinal cord is dorsal at the back of the heart and gut

28. What are the changes that occurred between less to more complex vertebrates?
Changes in size
Changes in relative size of different parts of the brain–cerebral cortex ,cerebellum
Changes in representation of the body on the
sensory cortex and locomotion
Cortical specialistion (association cortex)
Complexity of circuits
Vascularity, variety of non-neuronal cells
Changes in time course of development
Thank you...