Theories of Evolution

Lamarck’s Explanation ( )  Hypothesized that similar species descended from the same common ancestor  Acquired traits – traits that arise during an organism’s lifetime because of their experiences or behaviors

Beginning of the Modern Theory  In the mid 1800’s both Charles Darwin and Alfred Wallace proposed the theory of Natural Selection.  Organisms best suited to their environment reproduce more successfully than others.

Charles Darwin  Published the Origin of Species in 1859  Sailed around the world on the HMS Beagle studying different species in their natural environment  Did a lot of his studies in the Galapagos Islands

Darwin’s Theories Descent With Modification  Newer forms of organisms appearing are actually modified descendants of older species

Darwin’s Theories Modification By Natural Selection  This theory states how evolution occurs  Darwin agreed w/Malthus’ views on human population – have the potential for growing unchecked but are limited by adverse conditions  Environment limits growth of populations

Modification by Natural Selection  Some organisms have traits that make them more suitable for coping with their environment.  Organisms with more of these traits tend to leave more offspring

Evidence For Evolution The Fossil Record  Shows a long history of life on Earth  Shows that forms of organisms appeared, lasted for long periods of time, then disappeared to be followed by newer forms of life

Fossils  Trace of organisms  Develop from hard parts – shells, bones, teeth  Law of Superposition- Sedimentary rock layers - lowest layer is oldest  Relative Age  Absolute Age

Evidence for Evolution Comparative Anatomy – study of structural similarities and differences among living things The presence of certain types of similarities offers evidence for the evolutionary relationships between species.

Homologous structures  Parts of different organisms that have similar structures and similar embryological development, but have different forms and functions  Give evidence that some species may have evolved from common ancestors  Ex. Structure of arm and hand of human, whale, cat, bird, bat

Analogous Structures  Structures that have similar external form and functions but different internal structures  Ex. Wings of moth and bird

Vestigial Structures  Remnants of structures that were functional in an ancestral form  Ex. Appendix, human tailbone, pelvic bones of snakes

Evidence for Evolution Embryological Similarities  Embryos of closely related species show similar patterns of development  Ex. Fish, pig and human embryos look similar see page 223 or color plate 5-3

Evidence For Evolution Macromolecule Similarities  Molecular level – homologous proteins  Ex. The amino acid sequences in hemoglobin molecules of different species are similar  The more similar the homologous proteins are in different species, the more closely related the species are thought to be

Patterns of Evolution Coevolution  Change of two or more species in close association with each other  Ex. Long-nosed fruit bat has coevolved with the flowers they feed on  Predator-prey relationships and parasite-host relationships often coevolve

Patterns of Evolution Convergent Evolution  Organisms that seem very similar but not closely related at all  Occurs when environment selects similar phenotypes even though ancestral types were quite different  Ex. Sharks and porpoises

Patterns of Evolution Divergent Evolution  Two or more related populations of species become more and more dissimilar  Almost always as a response of differing habitats and can ultimately result in a new species

Divergent Evolution Adaptive Radiation  Many species evolve from a single ancestral species – ex. Galapagos Finches Artificial Selection  Process of speeding up divergence artificially- ex. Dog breeding