Beginnings: The Big Bang

Earth formed more than 4 billion years ago

Nanobes

Life in Thermal Pools

Conditions on Early Earth Organic compounds

spontaneously • self-assemble under

conditions possible on early Earth

Alternatively, compounds might have formed • in deep space and

reached earth in meteorites

Stanley Miller & Urey experiment

How Did Cells Emerge?

Self-replicating genetic systems require proteins (including enzymes) and nucleic acids

Proteins and nucleic acids may self-assemble•Form proto-cells• when certain conditions are met

•Clay-template hypothesis•Hydrothermal vent hypothesis

Origins of Self-Replicating Hypothesis: RNA world•RNA stores genetic information, but

breaks apart easily and mutates often•Ribozymes: Catalytic RNAs

Switch from RNA to DNA •Makes the genome more stable Early

Life

Early Life

The First Cells 3.8 billion years ago

• oxygen levels in atmosphere and seas were low • early prokaryotic cells probably were anaerobic

Divergence • separated bacteria from ancestors of• archaeans and eukaryotes

Cyanobacteria evolved • oxygen-releasing, noncyclic pathway

Increased oxygen favored aerobic respiration• ATP-forming metabolic pathway• Key innovation in evolution of eukaryotic cells

Stromatolites

Where did organelles come from?

Eukaryotic internal membranes may have evolved through infoldings of cell membrane

Endosymbiosis

One cell enters and survives inside another

Host and guest cells come to depend upon one another for essential metabolic processes

Mitochondria and chloroplasts may have evolved by endosymbiosis

Early Discoveries 19th century

• advances in geology, biogeography, and comparative morphology

• awareness of change in lines of descent of species

Development of new theories

Evolution•Change that occurs •line of descent

19th-century naturalists •tried to reconcile traditional beliefs

with evidence of evolution•Lamarck’s theory of inheritance of

acquired characteristics•Giraffe’s long neck

Voyage of the Beagle Charles Darwin’s observations on a

voyage around world led to new ideas about species

Descent with Modification

Darwin compared •modern armadillo with the extinct

glyptodont

Variations in Traits Darwin observed •variations in traits influence an

individual’s ability to secure resources – to survive and reproduce

Darwin, Wallace, and Natural Selection

In 1858, Charles Darwin and Alfred Wallace independently proposed a new theory, that natural selection can bring about evolution

What is evolution? Population• Individuals of the same species in the same

area•same number and kinds of genes same traits

Populations evolve •Traits that help characterize a population (and

a species) can change over generations Gene pool•All the genes of a population

Evolution •Change which occurs in a line of descent

What is natural selection?

Natural selection• In natural populations• Differential survival and reproduction among

individuals that vary in one or more heritable traits

Theory of Natural Selection•differential in survival and reproduction

among individuals of a population •Exhaust resources of its environment •lead to increased fitness • individual’s adaptation

• Individuals must compete for resources •food and shelter from predators

•more competitive tend to produce more offspring

•natural selection

Variation in heritable traits

some trait forms are more adaptive than others•bearers more likely to survive and

reproduce over generations, adaptive forms of

traits tend to become more common in a population• less adaptive forms of same traits

become less common or are lost

Fossil evidence Fossils •Physical evidence of

life in distant past Found in stacked

layers of sedimentary rock•Younger fossils in

more recently deposited layers

•Older fossils underneath, in older layers

Geologic time scale major intervals

determined fossil record

Correlated with macroevolutionary

events Major patterns,

trends, rates of change

among lineages Includes dates obtained radiometric dating

Comparative morphology Comparisons body form

and structure of major groups of organisms

Reveals evolutionary connections

Homologous structures: • similar body parts

that became modified differently in different lineages

Evidence of descent from a common ancestor

Morphological Convergence

Analogous structures: body parts in different lineages

look alike, but evolved separately after • lineages

diverged did not evolve in a

common ancestor

What is mutation ? Life’s diversity arises from mutations •Changes in molecules of DNA which

offspring inherit from their parents In natural populations, mutations introduce

variation in heritable traits among individuals

Super rats

Variation?

Individuals who inherit different combinations of alleles vary in details of one or more traits•Polymorphism: Several alleles in a

population Mutations are the original source of

new alleles•Lethal mutations result in death•Neutral mutations neither help nor

hurt

When is A population not evolving?

Genetic equilibrium•A state in which a population is not

evolving•Never occurs in nature