Evolution Biology 20

Evidence of Evolution Evolution: all changes that have occurred in living things since the beginning of life. If history of Earth is condensed to one 24-hour day: Earth is formed at the beginning of midnight Prokaryotes appear about 5:00 in the morning Eukaryotes present at 4:00pm in the afternoon Invasion of land starts about 10:00pm at night Humans appear 30 seconds before midnight at the end of the day

Fossil Evidence Fossils are remains, traces or other direct evidence of past life forms Most fossils form from the burial of plants and animals in the sediment Most fossils are embedded in sedimentary rock Paleontologists study the fossil record based on the boundaries between the strata, this helps determine the relative age of fossils Fossil links combined with modern comparative anatomy allows us to deduce vertebrate descent: Fish  amphibians  reptiles  birds and mammals

Evolution of the Modern Horse One of the few animals for which we have a fairly complete evolutionary record is the horse, as all the main stages of horse evolution have been preserved in fossil form. Over 60 million years the horse evolved from a dog-sized rainforest-dwelling creature, into an animal adapted to plains-dwelling and standing up to 2 metres high. In the process it traded-in its multi-toed feet, adapted for walking across the forest floor, for single-toed hooves, suited for running over open country.

Geological Time Scale Geological history of Earth is divided into eras and periods Fossil record provided relative dating of rock layers; top layer of rocks are younger than lower layers of rock Absolute dating methods uses radioactive isotopes

Biogeographical Evidence

Anatomical Evidence Homologous & Analogous Structures Vestigial Features

Homologous and Analogous Structures

Comparative Embryology

Biochemical Evidence DNA base sequences differences is DNA between a number of organisms shows less difference the more closely related they are; for example, 2.5% difference between humans and chimpanzees but 42% difference between humans and lemurs.

Contributors to the Theory of Evolution Linneaus Developed the classification system (binomial nomenclature) Linneaus did not believe in evolution, but his classification system helped to organize many organisms to show similar ancestry Larmark Recorded the first theory of evolution Two major disputable points: Nature has an innate tendency to evolve in the direction of increasing complexity, determined by the interaction with environment Acquired characteristics will be passed onto offspring (not genetically acquired)

Other Contributors to the Theory of Evolution Charles Darwin Studied medicine and theology At 22 became a naturalist on the HMS Beagle which sailed through the Galapagos Islands Proposed the Theory of Natural Selection Alfred Wallace Proposed the same idea as Darwim

Theory of Natural Selection Natural selection is a theory that proposes that individuals whose genetic variation best adapt them to their environments will be most likely to survive and pass on those traits.

Darwin’s Discovery of the Theory of Natural Selection (Fact 1) There is a potentially exponential increases in population  Overpopulation + (Fact 2) Population sizes are relatively stable (observation) (Fact 3) Resources are limited = (Inference 1) There is a struggle for existence (Fact 4) Individuals are unique (observation)  Variation (Fact 5) Many characteristics are inherited (Inference 2) There is a differential survival, that is natural selection Survival of the Fittest (Fact 6) The Earth is very old (Inference 3) Through many generations species evolve  Origin of species by inheritance of successful variation

Key Points of Natural Selection Individual differences are essential for evolution The struggle in nature that is of greatest consequence to evolution is not that between different species; rather, it is the competition within a population of a single species to obtain food, attract a mate, escape predators, etc. Only the difference that are inherited are relevant to evolution Evolution generally takes a great deal of time and is ongoing.

Sources of Inherited Variation Due to mutations (changes in DNA) which are random May be harmful, beneficial or neutral Sexual reproduction allows for variation as opposed to asexual where all organisms are identical to the parent

Inherited Variation Beneficial mutations increase fitness and reproductive success of an individual and therefore may become more common in a population Harmful mutations decrease fitness and reproductive success and therefore do not tend to accumulate

Speciation Speciation – formation of a new species Allopatric Speciation – speciation by reproductive isolation

Rate of Evolution Theory of Gradualism – speciation takes place slowly Theory of Punctuated Equilibrium – species evolve rapidly followed by period of little or no change

The earth has experiences period of rapid diversification of living things – divergent evolution – as well as episodes of mass extinction.