Development of Evolutionary Thought

Isn’t evolution “just” a theory? Scientific theories are explanations that are based on lines of evidence, enable valid predictions, and have been tested in many ways.Scientific theories are explanations that are based on lines of evidence, enable valid predictions, and have been tested in many ways.

Evolve – change over time

What is Evolution? Evolution - a change in the genetic composition of a population over time. Evolution - a change in the genetic composition of a population over time.

Paleontology & Evolution Older layers of sedimentary rock (the layers on the bottom) contain fossil species very dissimilar from modern life. Older layers of sedimentary rock (the layers on the bottom) contain fossil species very dissimilar from modern life. Each layer (stratum) is characterized by a unique group of fossil species. Each layer (stratum) is characterized by a unique group of fossil species. As you move upward through the layers, you find species more and more similar to modern life. As you move upward through the layers, you find species more and more similar to modern life.

James Hutton A Scottish geologist A Scottish geologist proposed that it was possible to explain the various landforms by looking at mechanisms currently operating in the world proposed that it was possible to explain the various landforms by looking at mechanisms currently operating in the world Proposed that the earth was much more than a few thousand years old Proposed that the earth was much more than a few thousand years old

Jean Baptiste Lamarck Theory of evolution in 1809 Theory of evolution in 1809 mechanism: mechanism: –use and disuse - the idea that the parts used the most grow stronger; the parts that don’t get used deteriorate –inheritance of acquired characteristics - the modifications that an organism acquires during its lifetime can be passed along to its offspring recognized adaptation to environment as a primary product of evolution recognized adaptation to environment as a primary product of evolution

Charles Darwin ( )  Father of modern evolutionary theory  Born in England  HMS Beagle  Galapagos Islands

The Galapagos Finches

What is an adaptation? An inherited characteristic that increases an organism’s ability to survive and reproduce in its specific environment. An inherited characteristic that increases an organism’s ability to survive and reproduce in its specific environment.

Darwin’s Observations Darwin noticed that every bird on the Galapagos Islands was a modified finch. Darwin noticed that every bird on the Galapagos Islands was a modified finch. The only differences in the birds were their beaks and what they ate. The only differences in the birds were their beaks and what they ate. These finches looked very similar to one type on South American continent, but none of these were found in S.A. These finches looked very similar to one type on South American continent, but none of these were found in S.A. “How did one species change into a different species?”

He wrote On The Origin of Species (1859) after 20 years of study.

Darwin’s Four Postulates Individuals within a population vary in their traits. Individuals within a population vary in their traits. Some of these traits are heritable. Some of these traits are heritable. More offspring are produced than can survive because of limited resources. More offspring are produced than can survive because of limited resources. Individuals with advantageous traits will survive and reproduce. Individuals with advantageous traits will survive and reproduce.

What is natural selection? Natural selection - a population of organisms can change over generations if individuals having certain heritable traits leave more offspring than others Natural selection - a population of organisms can change over generations if individuals having certain heritable traits leave more offspring than others Natural selection is the mechanism by which evolution is proposed to occur Natural selection is the mechanism by which evolution is proposed to occur

What is “artificial selection”? Nature provides the variation among different organisms, and humans select variations that they find useful. Nature provides the variation among different organisms, and humans select variations that they find useful. Example: breeding cows, horses, hogs Example: breeding cows, horses, hogs Darwin used this to help support his case for natural selection. Darwin used this to help support his case for natural selection.

Descent with modification  the history of life is like a tree, with multiple branching and re-branching from a common trunk all the way to the tips of the youngest twigs  most branches of evolution are dead ends; about 99% of all species that have ever lived are extinct

Figure 22.7 Descent with modification

Survival of the Fittest Another name for Darwin’s theory of natural selection. Another name for Darwin’s theory of natural selection. Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it.Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it.

Mechanisms of Evolution

Natural Selection & Survival of the Fittest (already discussed with Darwin)

Modern Ideas Darwin + Mendel’s work and the work of others, have lead to modern ideas about evolution. Darwin + Mendel’s work and the work of others, have lead to modern ideas about evolution. Another mechanism of evolution is Genetic Drift (random changes in genes) which occurs through natural selection.

Modern Ideas Speciation – formation of new species is due to gradual genetic changes, and that large scale evolution is the result of a lot of small scale evolution. Speciation – formation of new species is due to gradual genetic changes, and that large scale evolution is the result of a lot of small scale evolution. Microevolution – process responsible for the variations that exist within a species, or a change in the allele frequency. Microevolution – process responsible for the variations that exist within a species, or a change in the allele frequency.

Modern Ideas Macroevolution – evolution that occurs between species. Macroevolution – evolution that occurs between species. Examples: the separation of a species to form two distinct species or the development of a new species from many small changes within an existing species Examples: the separation of a species to form two distinct species or the development of a new species from many small changes within an existing species

Gene Flow The change in occurrence of genes in a population. This occurs when an individual leaves a population (emigration) or new individual joins a population (immigration). The change in occurrence of genes in a population. This occurs when an individual leaves a population (emigration) or new individual joins a population (immigration).

Genetic Drift Random changes in the occurrence of genes through chance events. Random changes in the occurrence of genes through chance events. Can occur when a few individuals of a population break off from the original group and start their own population (founder effect). Can occur when a few individuals of a population break off from the original group and start their own population (founder effect). Large number of population is killed due to disease, starvation, natural disaster, etc. (bottle necking) Large number of population is killed due to disease, starvation, natural disaster, etc. (bottle necking)

Punctuated Equilibrium Darwin felt that biological change was slow and steady as indicated in the fossil record. Darwin felt that biological change was slow and steady as indicated in the fossil record. Modern scientists see that this pattern does not always hold. (Darwin’s finches) Modern scientists see that this pattern does not always hold. (Darwin’s finches) The term punctuated equilibrium is used to describe a pattern of long, stable periods interrupted by brief periods of more rapid change. This is still controversial today. The term punctuated equilibrium is used to describe a pattern of long, stable periods interrupted by brief periods of more rapid change. This is still controversial today.

Evidence of Evolution

Fossil Evidence Fossils provided a detailed record of evolution. Fossils provided a detailed record of evolution. Fossils formed in different layers of rock were evidence of gradual change over time. Fossils formed in different layers of rock were evidence of gradual change over time.

Homologous Body Structures Structures in different species that may perform different functions but are similar because of their common ancestry Structures in different species that may perform different functions but are similar because of their common ancestry Vestigial organs - structures of no apparent function to an organism; leftover from ancestry; ex - snakes have leg & pelvis bones Vestigial organs - structures of no apparent function to an organism; leftover from ancestry; ex - snakes have leg & pelvis bones

Figure Homologous structures: anatomical signs of descent with modification

More homology… Molecular homology - similarity in DNA sequence between an ancestor and its progeny Molecular homology - similarity in DNA sequence between an ancestor and its progeny Embryological homology - similarities only apparent in embryological development Embryological homology - similarities only apparent in embryological development –ex: all vertebrate embryos have “pharyngeal pouches” which later become gills or Eustachian tubes

Patterns of Evolution

Adaptive Radiation When a single species or a small group of species has evolved into several different forms that live in different ways. When a single species or a small group of species has evolved into several different forms that live in different ways. Example: Darwin’s finches (more than a dozen evolved from a single species) Example: Darwin’s finches (more than a dozen evolved from a single species)

Convergent Evolution Convergent Evolution Explains how unrelated species can develop similar characteristics Explains how unrelated species can develop similar characteristics Porpoise (mammal) & Shark (fish) Porpoise (mammal) & Shark (fish) Unrelated animals, but share similar characteristics to suit their environment Unrelated animals, but share similar characteristics to suit their environment

Analogous structures Show similarity in structure based on adaptation for the same function, not common descent. Show similarity in structure based on adaptation for the same function, not common descent.

Divergent Evolution Divergent Evolution Suggests that many species develop from a common ancestor Suggests that many species develop from a common ancestor Penguins (wings for swimming) & vultures (wings for flying) Penguins (wings for swimming) & vultures (wings for flying) Both are birds, diverged from a common ancestor Both are birds, diverged from a common ancestor

Co-evolution When two or more organisms in an ecosystem evolve in response to each other. When two or more organisms in an ecosystem evolve in response to each other. Example: Flowers and their pollinators Example: Flowers and their pollinators

Camouflage – an animal looks like its environment

Mimicry- when animals have coloring and markings to look like another animal