Principles of Evolution

Chapter 24

Classification of Humans

• Kingdom Animalia

• Phylum Chordata

• Class Mammalia

• Order Primates

• Family Hominidae

• Genus Homo

• Species sapiens

Challenges to Early Beliefs

• Biogeography - discovery of species in isolated

locales

• Comparative morphology - similarities between

animals, parts with no functions

• Fossils - deep layers with simple fossils,

overlying layers with increasing complexity

Charles Darwin

• Proposed the theory of evolution by way of natural selection

• Influenced by– Observations made while naturalist on

H.M.S. Beagle

– Conversations with other naturalists

– Writings of Thomas Malthus

Variation in Populations

• Individuals do not evolve; populations do

• Members of a population have similar traits

• Details of traits vary among individuals

• Some variation results from genetic differences (different alleles)

Mutation

• A heritable change in DNA

• Most are harmful

• Some are neutral

• A few are beneficial

Natural Selection

• Individuals vary

• Some variations are heritable

• Some versions of traits increase fitness

• Natural selection is the difference in

survival and reproduction in individuals

who have different versions of a trait

Evolving Populations

• A population is evolving when some forms of a trait are becoming more or less common relative to the other forms

• Over time, shifts in the makeup of gene pools have been responsible for the amazing diversity of life forms on Earth

Other Changes to Gene Pool

• Genetic drift– Founder effect– Virtually no Native Americans with

type B blood

• Gene flow– Physical movement of alleles– Helps keep neighboring populations

genetically similar

Species

• A genetic unit consisting of one or more

populations of organisms

• Members can interbreed and produce

fertile offspring under natural conditions

• Reproductively isolated from other species

Speciation

time A time B time C time D

time

Fossils

• Usually hard parts

• Form in sedimentary rock

• Stratification

• Fossil record is biased

Biogeography

Distribution of plants and animals

Plate tectonics

Comparative Morphology

• Homology

– Similarity in body parts in different organisms

– Attributable to descent from a common ancestor

• Analogy

– Similarity in body parts in different organisms

– Attributable to similar environmental pressures

Homologous Structures

Vertebrate forelimbs

Comparative Embryology• Early vertebrate embryos strongly resemble one

another

• Same plan of development

Fish Reptile Bird Mammal

Proportional Skull Changes

Chimpanzee Human

Evidence from Comparative Biochemistry

• Molecular clocks

– Neutral mutations

• Protein comparisons

– Cytochrome C

• Nucleic-acid comparisons

– Base-pairing of DNA or RNA from one species

to another

Extinctions - End of the Line

• Background extinction

– Local changing conditions

• Mass extinction

– Catastrophic global event

– 65 million years ago

– Probably asteroid impact

Adaptive Radiation

• New species of a lineage moves into a wide range of habitats

• Has occurred in the human lineage

• Homo habilis remained in Africa

• H. erectus went to Europe, Asia

• H. sapiens evolved by 100,000 years ago

Trends in Human Evolution

• Upright walking

• Refined hand movements

• Enhanced daytime vision

• Changes in dentition

• Changes in brain and behavior

Comparison of Skeletal Organization

Trend toward Longer Life Spans and Dependency

From Primates to Hominids

• 60 million years ago– Tropical forests

– Small rodents, tree shrews

• 54 - 38 million years ago– Primates in trees

• 36 million years ago– Tree-dwelling anthropoids

• 10 - 5 million years ago– First hominoids

Early Earth

• Primitive atmosphere

– H2

– N2

– CO

– CO2

– Probably no O2

Complex Compounds Form

Organic compounds may have:

• Formed when lightning interacted with

gases in early atmosphere

• Assembled on clays in tidal flats

• Formed near hydrothermal vents

Emergence of First Living Cells

• Self-Replicating Systems

– RNA

– DNA

• Plasma Membranes

– Proto-cells