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