Evolution and Human Survival

Lecture 4

PSY391S

John Yeomans

Diversity of Life Forms

• Categorization by phenotypes.

• Linneaus: Species, genus, family, order class, phylum, kingdom.

• Which features are most important in making groups?

• Can the same principles be used to make other groups?

• How were these groups formed?

Diversity of Ancient Life

• Geology: Older fossil forms in deeper sediments.

• Changes in size, structure and design imply family histories. Evolution.

• Variety of habitats and fossils. Beagle.

• How did species evolve over millions of years?

• Darwin: “Survival of Fittest”

Evidence for Theory

• Historical Record: Wars, famines, diseases, habitat lossselection.

• Movement of species to new habitats new structures, e.g. lungs, legs, hair.

• How did this happen in prehistory?

• Selective breeding of domestic animals--pigeons, cows, dogs.

Speciation

• Finches in Galapagos--Darwin and Grants.

• When do phenotype differences become species differences?

• How did humans diverge from primates?

• Why did Neanderthals or other primates die?

How to Survive?

• “We are the accumulation of mechanisms that allowed our ancestors to survive and to reproduce their genes” (Sagan)

• “Accumulation” includes functional and vestigial systems. DNA also an accumulation.

• Who were our ancestors who managed to survive and reproduce?

• The Selfish Gene: All our systems and strategies are shells for helping our genes survive.

• Biological Purpose of Life?

Human Strategies• Survival: Kill others genes and save your

own? Humans survive by social cooperation rather than “dog eat dog”.

• Reproduction: Have the most offspring possible? Humans have the fewest--single births, long immature period--but highest survival rate.

• Learning and specialization--Civilization.

• Aggression? Yes, but not to disrupt social organization.

Classification and Gene Lineages

Lecture 5

PSY391S

John Yeomans

Classification by Phenotype

• Which features are most important? Little agreement.

• Principles of comparing different groups?

• Where is change from species to genus to family etc, if evolution is continuous?

• Genes are more fundamental, in theory, than any surface features.

• Quantitative rather than qualitative.

Classification by Genes

• Hybridization of DNA samples (Wilson).

• Complete sequences, genomes.

• Similarities in genes from flies to humans imply common lineages.

• Reconstruction of family trees: Are all bases equally important?

• Is DNA mutation rate constant?

• Genetic Clock~ 1%/5 million years.

Human Family History

• Females: Mitochondrial DNA is preserved from mother to daughter. 16,569 bases.

• Trace human origins to Eve? Neanderthals?

• Males: Y chromosome is preserved from father to son. Trace family lineage.

• Trace DNA in all humans to extract lineages around the globe.

Human Genes

• Which DNA makes us different from primates? E.g. prodynorphin.

• Are some genes more important?

• Which genes affect hands, brain, speech?

• Could a few genes lead to larger brains?

CNS Evolution--Invertebrates

• Nerve nets: Action potentials, reflexes.

• Ganglia chains: Molluscs, worms, arthropods.

• Giant neurons and axons--no myelin.

• Head ganglia are fused.

Lecture 6: Evolution of Brain

• Mammalian brain properties

• Brain size vs. body weight

• Ancient brains--when did they get bigger?

• Human brains--when did they get bigger?

Vertebrate CNS

• Protected brain and spinal cord.

• Myelinated axons saves space for more neurons.

• Shift from midbrain, cerebellum and olfaction to limbic system then cerebral cortex.

Brain Size and Body Weight

Equation

• Log Brain Weight=0.7(log Body Weight)+b

• Or: Brain Weight = K(Body Wt)0.7

• Power function linear on log-log plot.

• Some mammals have extra brain size (Humans and dolphins 8X extra)

• K = encephalization factor.

All Vertebrates

Ancient Vertebrates

• Brain weight from endocranial space.• Body weight from leg bone diameter.• Ancient reptiles same as modern reptiles,

except for Archeopteryx (bird-like predator).

• Modern birds and mammals increased brain capacity by 4X over ancient birds and mammals (still 4X reptiles).

• Warm blood favors brain evolution?

Encephalization

Evolution of Human Brain

• Increased by 3X about 1-2 million years ago.

• Most of change in frontal cortex.

• Neoteny: Do we sustain embryonic brain growth for longer by keeping neonate features?