EVOLUTION A SCIENTIFIC THEORY

I. The History Carl Linneaus (18 th 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 (18 th – 19 th century): Attempting to justify the conditions of the poor by stating that poverty and starvation were merely a consequence of overpopulation.

Lamarck (18 th – 19 th century) – First to publish a reasoned theory of evolution: A) the idea of use and disuse B) inheritance of acquired characteristics Lyell (19 th 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 (19 th – 20 th century): theory of evolution by natural selection.

Charles Darwin (19 th century) – theory of evolution by natural selection. Darwin’s dangerous idea:

II. What is a scientific theory? A widely accepted explanatory idea that is broad in scope and supported by a large body of evidence.

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 competing 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  

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 dating

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 so similar fossils from different continents could be found Developmental biology – the embryos of related species look similar during their early embryonic development.

Artificial selection – humans select traits of organisms for human benefits (domestication) Molecular comparisons:  Universal genetic code  Proteins and DNA (the closer related two species are the more similar their DNA and proteins are)

V. The Mechanisms of Evolution – any process that drives evolution and results in change in the genes of the population Types of natural selection:  Directional selection – one extreme phenotype or another is favored  Stabilizing selection – the middle (most common) phenotype is favored  Disruptive selection – both extremes are more beneficial then the most common phenotype

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 random chance  Founder 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.

VI. Examples of Evolution Industrial Melanism Human birth weight Heterozygous advantage Darwin’s finches Antibiotic and pesticide resistance

VII. Modern Evolutionary Theory Several scientists improved on Darwin’s theory and this improvement is still going on. We know that POPULATIONS EVOLVE NOT INDIVIDUALS Today we explain the causes of evolution with mutations, changes in DNA and sexual reproduction. Evolution is closely related to genetics.

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

VIII. Evolution of Populations Individuals cannot evolve, they have a set of genes that they cannot change. However, populations can. Populations – a group of organisms that look alike, belong to the same species and live in a given area Within the population there is variation to a given trait. This variation is frequently represented by a bell curve.

Causes of variation:  Environmental factors (like type of food source)  Crossing over and genetic recombination during meiosis and fertilization  Mutations Gene pool – the total genetic information available for a population. This can be used to predict all the genotypes and phenotypes in the population.

Allele frequency – the percentage of a certain allele in a population. Phenotype frequency – the percentage of a certain phenotype in a population

IX. The Hardy-Weinberg Equilibrium Allele frequencies in a population tend to remain constant under certain conditions, although the phenotype frequency may change – Hardy- Weinberg Equilibrium This equilibrium is based on the following assumptions:  No natural selection  No mutations  Large population  Random mating  No gene flow

Because evolution is the change in allele frequency in a population, if any of the above mentioned conditions change, evolution is occurring and the population is not in Hardy-Weinberg equilibrium. We can mathematically calculate the allele frequencies in the population by using the following: (We will practice lots of problems on this)