Evolution March 23, 2009

Jean-Baptiste Lamarck First scientist to propose a mechanism for how organisms change (1809) Theory of Acquired Traits Through time, a generation would use an organ more than previously, and would pass those traits on to their offspring.

Charles Darwin English naturalist Sailed around the world on the ‘Beagle’ His observations lead to theory of evolution

Why did some species survive while others became extinct?

Evolution = Change over time In Biology evolution is the change in a species over time How do species change?

Evolution - Fact vs. Theory Evolution is the change in the genetic make up of populations over time. All living things change. Evolution is a fact. Populations evolve, not individuals. The mechanism for evolution (how it happens) is a theory.

Theory of Natural Selection Within a population, there are natural variations. Farmers improved their plants and animals through selective breeding.

Farmers bred the plants or animals with most desired traits. This process of humans allowing only the best organisms to reproduce is called artificial selection.

“Survival of the Fittest” In nature, fitness is the ability of an organism to survive and reproduce in its environment. Individuals with characteristics best suited to environment survive the struggle for existence. This principle is called survival of the fittest.

Natural Selection The process by which nature allows only the organisms best suited to their environment to reproduce is called natural selection. I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.    —Charles Darwin from "The Origin of Species"

Natural Selection in Action Two variations of peppered moths (light and dark). Tree trunks light colored. Who will survive?

Light populations grew. Industrial revolution released soot into air - tree trunks darken… Now who will survive? Example of microevolution

Microevolution Small changes between generations Allele frequency Leads to macroevolution

Macroevolution Large scale changes over long periods of times Eliminate/create species

Mechanisms of Microevolution Mutation Migration Genetic drift Natural selection

Mutation Allele is changed by random mutation Mutation present in offspring and may be passed to next generation

Migration New individuals emigrate into population.

Genetic Drift By random chance, individuals mate and increase allele frequency

Natural Selection Survival of the fittest. Some individuals have traits making them more adapted to their environment.

Evidence for Microevolution Pesticide resistant insects Gene for pesticide resistance passed on through ‘fit’ survivors

Evidence for Macroevolution Fossil record Biochemistry & Molecular Biology Anatomy Vestigal structures Comparitive embryology

Fossil Record Fossils are the remains of ancient life. When fossils are arranged according to their age, a progressive series of changes are seen.

How Fossils are Formed Petrification - Organic material replaced by minerals Mold & Cast - Form of organism after rots away Carbonization - All element except carbon removed Unaltered Preservation - Original state (amber)

Law of Superposition Each layer of rock is older than the layer above it. Fossils arranged by age relative to each other Radioactive Dating Used to date layers in which fossils occur. Allows time frame of when fossil was formed

Biochemistry & Molecular Biology All organisms from bacteria to humans share many of the same biochemical details. The genetic code for protein-coding genes All organisms use ATP Plasma membranes of all organisms are structurally similar (phospholipid bi-layer)

Anatomy Homologous structures are parts of different organisms, often quite dissimilar, that develop from the same ancestral part.

Analogous Structures Analogous structures have similar form & function, but are structurally quite different

Vestigial Structures Traces of structures no longer used by organism. May be reduced version of homologous structures in other species.

Comparative Embryology Embryos of many animals with backbones look so similar they are hard to tell apart.

Human Embryo Characteristics Early in their development, embryos posses gill slits like those of fish. Later in development, the embryos develop a tail. Human fetuses have a fine fur (lanugo) during the fifth month of development

So far… Darwin & Natural Selection How species evolve between generations Evidence for evolution How do we get new species?

Speciation Changes leading to formation of new species. Populations evolve and become reproductively isolated from each other (members of two populations cannot interbreed) Behavioral isolation Geographic isolation

Behavioral Isolation Capable of interbreeding, but have different courtship rituals.

Geographical Isolation Populations separated by geographic barriers (rivers, mountains, bodies of water, etc.) Doesn’t always lead to new species.

Patterns of Evolution Adaptive Radiation Small group of species evolve into different forms that live in different ways.

Patterns of Evolution Convergent Evolution Unrelated organisms begin to resemble each other. Similar environmental demands

Patterns of Evolution Coevolution Two species evolve in response to changes in each other.

Summary