Theories of Evolution
Lamarck’s Explanation (1744-1829) 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 EvolutionThe 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 EvolutionComparative 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 EvolutionMacromolecule 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 EvolutionCoevolution 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 EvolutionAdaptive Radiation Many species evolve from a single ancestral species – ex.
Galapagos FinchesArtificial Selection Process of speeding up divergence artificially- ex. Dog
breeding