EVOLUTION

A SCIENTIFIC THEORY

I. The HistoryCarl Linneaus (18th century)– The

father of taxonomy. Used binomial nomenclature, came up with the hierarchical classification theme, used visible characteristics to classify plants and animals.

Thomas Malthus (18th – 19th century): Attempting to justify the conditions of the poor by stating that poverty and starvation were merely a consequence of overpopulation.

http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html

Lamarck (18th – 19th century) – First to publish a reasoned theory of evolution: A) the idea of use and disuse B) inheritance of acquired characteristics

Lyell (19th century) – natural processes form geological formations over a long period of time, erosion and other forces that shape rocks are very slow processes that take millions of years, so the earth must be older than previously believed.

Wallace (19th – 20th century): theory of evolution by natural selection.

Charles Darwin (19th century) – theory of evolution by natural selection.

II. What is a scientific theory?

A widely accepted explanatory idea that is broad in scope and supported by a large body of evidence.

http://www.pbs.org/wgbh/evolution/library/11/2/e_s_1.html

III. Natural Selection

Natural Selection: The process in nature by which, only the organisms best adapted to their environment tend to survive and transmit their genetic characteristics in increasing numbers to succeeding generations while those less adapted tend to be eliminated. As a result the POPULATION EVOLVES – or changes over time.

The five aspects (steps) of natural selection:Variation – individuals exhibit variation in a

population, they have a unique set of traits. Some of these traits improve their chances of survival while others are less favorable.

Overproduction – populations produce too many young, many must die.

Struggle for existence – food, water and other resources are limited, organisms are compete with one another for these resources.

Differential reproductive success – those individuals that have the most favorable characteristics in an environment, has higher chance of reproduction.

Descent with modification – the varying reproductive success result in a change in the population – the more successful traits become more common

http://www.pbs.org/wgbh/evolution/library/01/6/quicktime/l_016_08.html http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html

IV. Evidence of Evolution

The fossil record – remains or traces of previously lived organisms (shells, amber, prints, skeletal remains). Mostly found in sedimentary rocks

Their age can be determined by radiometric datinghttp://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html

Comparative anatomy: homologous structures – structures that have similar origins but may look different from the outside. Analogous structures -- may look similar but have different origins

Vestigial structures – structures that are not used any more but were used by our ancestors

Biogeography of animals and plants and continental drifts (geographic distribution of species) – organisms with similar origin tend to live in the same area

http://www.ucmp.berkeley.edu/geology/anim1.html -- so similar fossils from different continents could be found

Developmental biology – the embryos of related species look similar during their early embryonal development.

Artificial selection – humans select traits of organisms for human benefits (domestication)

Molecular comparisons:Universal genetic codeProteins and DNA (the closer related two

species are the more similar their DNA and proteins are)

Molecular clocks

Biogeography – geographic distribution of species.

V. The Mechanisms of Evolution

Natural selection – you already know this one.

Mutations (small changes in the nucleotide sequence of DNA) result in new traits and increasing variation in the population. One mutation alone usually does not change the population, however, beneficial mutations can cause some change

Genetic drift – change in the allele frequency in a population based on chanceFounder effect – small group of organisms

move away from the main population and give rise to a new population

Bottleneck effect – after a natural disaster, a small group of organisms with different characteristics survive

Gene flow – movement of organisms from one population to another

Nonrandom mating – sexual selection, selecting mates because of their visual traits.

http://www.youtube.com/watch?v=cEh-zclVo44

VI. Examples of EvolutionIndustrial MelanismHuman birth weightHeterozygous advantageDarwin’s finchesAntibiotic and pesticide resistance

VII. Modern Evolutionary TheorySeveral scientists improved on Darwin’s

theory and this improvement is still going on. We know that POPULATIONS EVOLVE NOT

INDIVIDUALSToday we explain the causes of evolution

with mutations, changes in DNA and sexual reproduction.

Evolution is closely related to genetics.

http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

Today’s definition of evolution: Genetic change in a population or species over generations; all the changes that transform life on Earth; these heritable changes produced Earth’s diversity of organisms

Just for fun: http://www.youtube.com/watch?v=T1_vnsdgxII