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