Evolution Darwin’s Theory of Evolution Evolution of Populations The History of Life Classification

Evolution = Theory = “Change over time” The process by which modern organisms have descended from ancient organisms A verb!!! NOT a noun!!! Theory = A well-supported testable explanation of phenomena that have occurred in the natural world Based on measurable observations of the natural world

Microevolution – Macroevolution – Describes the details of how populations change from generation to generation Describes how new species originate Macroevolution – Describes patterns of changes in groups of related species over broad periods of geologic time Determines the phylogeny (evolutionary relationships) among species/groups of species

Darwin’s Theory of Evolution

Voyage of the H.M.S. Beagle (1831-1836) As Darwin made observations on his journey he wondered about… Why were many plants and animals well suited to the habitat in which they were found? Puzzled by where plants and animals lived and did not live. Were fossils related to species still around today? Darwin was also intrigued by the tortoise diversity on the Galapagos Islands.

Ideas that shaped Darwin’s Thinking Hutton’s theory of Geologic Change (1785) – Earth is shaped by geological forces that took place over extremely long periods of time Earth is millions of years old (not thousands) Thomas Malthus (1798) – Predicted that the human population will grow faster than the space and food supplies needed to sustain it

Ideas that shaped Darwin’s Thinking Jean-Baptiste Lamarck (1809)– 1st to propose a theory of how organisms change over time (Use and disuse, Inheritance of acquired traits, tendency toward perfection) Incorrect theory  an organism’s behavior has no effect on heritable characteristics!!! Lyell’s Principles of Geology (1833) – Processes occurring now have shaped Earth’s geological features over long periods of time.

On the Origin of Species Darwin did not rush to publish (waited 25 years!) Published his work because of Alfred Wallace (who had similar theories) 1859 – On the Origin of Species Caused a controversy because the theory radically challenged church doctrine

Evolution by Natural Selection Struggle for Existence – Members of each species compete to obtain food, living space, and other resources necessary for life Survival of the Fittest – Individuals that are better suited to their environment survive and reproduce most successfully. Fitness  ability to survive and reproduce Adaptation  any inherited characteristic that increases an organism’s chance at survival

Evolution by Natural Selection Descent with Modification – Species today look different from their ancestors Natural selection produces organisms that have: Different structures Establish different niches Occupy different habitats All living organisms are related to one another

Evidence of Evolution Evidence includes: The fossil record Geographic distribution Homologous and Analogous structures Similarities in Embryology Similarities in Biochemistry (review the activities done for each of these)

Evolution of Populations

Genetics and the Environment The characteristics of organisms  not solely determined by inherited genes Determined by interaction between genes and the environment Genes provide a plan for development  how the plan unfolds also depends on the environment

Genes and Variation 2 main sources of genetic variation: Mutations Gene shuffling during sexual reproduction Gene pool  all genes (and alleles) that are present in a population Relative frequency  # of times an allele occurs in a gene pool (given as a percentage) Evolution is any change in the relative frequency of alleles in a population

Natural Selection and Evolution Natural Selection never acts directly on genes Works on the entire organism…can only affect which individuals survive and reproduce If an individual dies  does not pass on genes ALSO…Individuals do not evolve…Populations evolve as the gene pool changes because of the relative frequency of the alleles changes

Natural Selection and Genetic Change Single-Gene traits  leads to changes in allele frequencies (thus to evolution) Natural Selection on Polygenic Traits  leads to changes in the distribution of phenotypes (3 ways): Directional Selection Stabilizing Selection Disruptive Selection

Directional Selection

Stabilizing Selection

Disruptive Selection

How do Populations Evolve? Natural Selection in not the only source of evolutionary change Genetic drift  Individuals that carry a particular allele may leave more descendents BY CHANCE. Over time, a series of chance occurrences can cause an allele to become common in a population A new species can result if there is enough of a genetic difference between the original population and the new population

Evolution vs. Genetic Equilibrium Hardy-Weinburg Principle  allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change Constant allele frequencies = genetic equilibrium

Hardy-Weinburg In order to maintain genetic equilibrium there are several conditions that must be met: Random mating Large population No movement into or out of the population No mutations No Natural Selection Refer to the activity for review

The Process of Speciation Formation of a new species (organisms that breed and produce fertile offspring) As new species evolve, populations become isolated from one another Reproductive isolation  members of 2 populations can no longer interbreed and produce fertile offspring

Isolating Mechanisms Behavioral Isolation  differences in courtship or other reproductive strategies that involve behavior Geographic Isolation  2 populations are separated by geographic barriers Temporal Isolation  2 or more populations reproduce at different times of the year

Case Study: Darwin’s finches Evolution of Darwin’s finches  Founders arrive Separation of populations Changes in the gene pool Reproductive Isolation Ecological Competition Continues Evolution

Patterns of Evolution 4 main patterns  Divergent Evolution: 2 or more species originate from a common ancestor Convergent Evolution: 2 unrelated species that share similar traits (independent adaptation to the environment) Parallel evolution: 2 related species (lineages) that have made similar changes after the common ancestor Coevolution: evolution of one species in response to new adaptations in another (predator/prey relationship)

Divergent Evolution

Convergent Evolution

Parallel evolution

Coevolution

Macroevolution 2 distinct theories: Gradualism Punctuated Equilibrium Evolution occurs by the gradual accumulation of small changes Punctuated Equilibrium Evolutionary history consists of geologically long periods of stasis with little or no evolution, interrupted by geologically short periods of rapid evolution

Gradualism

Punctuated Equilibrium

The Origin of Life: Chemical Evolution The following is a hypothesized order of events that led to life on Earth: The Earth and its atmosphere formed Outgassing of the molten interior (CO, CO2, H2, N2, H2O, S, HCl, HCN) The primordial seas formed Complex molecules were synthesized Oparin/Haldane and Miller experiments

Life on Earth (continued) Polymers and self-replicating molecules were synthesized Organic molecules were concentrated and isolated into protobionts Primitive heterotrophic prokaryotes formed Primitive autotrophic prokaryotes were formed

Life on Earth (continued) Oxygen and the ozone layer formed and abiotic chemical evolution ended Eukaryotes formed (“endosymbiotic theory”) Originated from a mutually beneficial association among various kinds of prokaryotes Mitochondia, chloroplasts possess their own DNA, reproduce independently of the cell, resembles bacteria and cyanobacteria

Standard Classification Developed by Carolus Linnaeus in the 18th century Organizes organisms into groups and subgroups based on evolutionary relationships Often revised when new relationships are discovered (DNA evidence) Example: Pseudocalanus spp.

Classification levels: Kingdom (broad) Phylum Class Order Family Genus Species (specific)