Chapter 10: Principles of Evolution

What is Evolution? Evolution is the process of biological change by which descendants come to differ from their ancestors It is the central theme in all fields of Biology

Carolus Linnaeus Developed a classification system for all types of organisms Organisms were grouped by similarities but also reflected evolutionary relationships

Georges Louis Leclerc de Buffon Proposed that species shared ancestors instead of arising separately Suggested that Earth was much older than 6,000 years old which was the common belief at the time

Erasmus Darwin Charles Darwin’s grandfather Proposed that all living things were descended from a common ancestor and that more-complex forms of life arose from less-complex forms

Early misconception by Jean-Baptiste Lamarck (1809) Proposed all organisms evolved toward perfection and complexity Use and Disuse of Organs Theory—organisms respond to their environment by developing new structures as needed The more an organ was in use, the bigger it would become and vice versa Inheritance of Acquired Traits—these traits are passed on to offspring Ex. giraffes

Lamarck continued… http://www.princessleia.com/images/MyImages/essays/giraffe_lamark.jpg

Lamarck cont. In order for groups of organisms to have adapted over time, populations must have evolved rather than individuals.

Charles Darwin (1809-1882) An English scientist who formed ideas that are now the basis of modern evolutionary theory When he was 21, Darwin took an apprenticeship on a 5-year scientific voyage on the HMS Beagle He was the unofficial naturalist on the ship collecting many specimens along the way

Darwin’s voyage (Page 277) Darwin's journey The Galapagos Islands, off the coast of Ecuador, became the focal point in Darwin’s observations

In 1859, Darwin published his theories and ideas in the book On the Origin of Species by Natural Selection

Variation is the difference in the physical traits of an individual from those of other individuals in the group to which it belongs Can occur either among members of different species (interspecific) or same species (intraspecific)

Darwin believed that variation arose when species adapted to their surroundings. An adaptation is a feature that allows an organism to better survive in its environment An adaptation can lead to genetic change in a population over time

Artificial selection Darwin also conducted many breeding experiments with pigeons and found that organisms with specific traits could be crossed to result in offspring that had those selected traits; this is called artificial selection Humans are the selecting agent in artificial selection

In order for—artificial or natural—selection to occur, the trait must be heritable. Heritability is the ability of a trait to be passed down from one generation to the next Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. The environment (nature) is the selective agent

Four main principles to the theory of natural selection Variation Individuals in a population have varying characteristics Overproduction Organisms tend to produce more offspring than can survive to maturity Adaptation The traits of survivors will become more common in a population Descent with modification Surviving individuals tend to reproduce more than others

Overview of the Evolution Theory Variation exists within the genes of every population or species (as a result of random mutation) In a particular environment, some individuals of a population or species are better suited to survive (a result of variation) and have more offspring (natural selection)

Overview cont. 3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population 4. There is a clear proof from fossils and many other sources that living species evolved from organisms that are extinct.

Natural selection acts on phenotypes or physical traits, rather than on genetic material itself.

Evidence for Evolution Fossil Record Geography Embryology Body Structures (Anatomy) Biochemistry (Genes and Proteins)

Fossil Record Fossils of animals show a pattern of development from early ancestors to their modern descendants “Intermediate” (missing links) species show how organisms evolved new adaptations Fossil Evidence Examples

Problems with fossils It is difficult to find fossils of soft-bodied organisms with no hard parts that can be left behind Organisms decay at different rates and may not leave any traces

Geography Shows similarities among species living on different areas “Descent with modification”

Embryology Most embryos look very similar and have gill slits and tails. This suggests a common ancestor.

Anatomy Comparing structures of related organisms to find relationships between organisms Ex. Homologous Structures Comparing Primate Skeletons Comparing common structures between unrelated organisms to find how natural selection affects organisms in similar environments Ex. Analogous Structures

Homologous Structures Have a common evolutionary origin Similar structure but different functions

Analogous Structures Structures that are similar in function but do not have a common evolutionary origin Different structures but similar functions Ex. Bird wing and an insect wing Shows that different species evolved similar traits to overcome similar selective agents

Homologous structures versus Analogous structures

Vestigial Structures A body structure that has no function presently but was probably useful to an ancestor Even though the species does not need the feature, the structure is still passed on to offspring Ex. Eyes on blind mole-rats, flightless wings on an ostrich, appendix/tonsils on humans

Biochemistry As organisms evolve, the differences in the amino acids, DNA, and proteins they make should change gradually The more amino acid differences there are between two organisms, the more distantly related they are