Natural Selection

A Brief Overview

“Descent with Modification”• Species change over time = hot idea in 1700’s• G. Cuvier noted fossils in rock strata– “Catastrophism” explains abrupt changes in fossils

• C. Lyell, geologist, was for “uniformitarianism”– Geological forces of past still working today

• J.B. Lamark supported spontaneous generation & inheritance of acquired traits– Neither of these explanations is accepted today

Lexington, KY: Ordovician Period Fossils450 million years ago

“Descent with Modification” “Natural Selection”

• Evolution proposed by others already– Anaximander (611-546 B.C.) 1st Westerner– Erasmus Darwin (Charles’ grandfather)

• Charles Darwin & Russell Wallace present idea of evolution to scientific community in France

• Charles Darwin (1859) published On the Origin of Species by Means of Natural Selection.– Descent with Modification = process of evolution– All current life descended from 1 (or few) life forms – Species must be able to change over time

Darwin’s Grounds for Evolution

• Observations during sea trip around world– Galapagos Islands’ distinct populations• Finches, tortoises, mockingbirds, etc…

– Plant & animal comparisons among continents• Prickly pear, octopus, birds, insects, lizards, mice, coral

• Writings from Lyell on fossils & rock strata• Notes from grandfather Erasmus Darwin• T. Malthus’ writings on population pressures

Basis For Natural Selection1) Overproduction

More offspring are produced than can survive.

2) Genetic VariationIndividuals have range of traits.

3) Struggle to SurviveCompetition and Adaptation favor “best fit”.

4) Differential Reproduction“Adaptation”- best survive & out-reproduce others“Acclimatization” – personal adjustments

Evidence for Evolution I• Biological Linnaean Classification– Implied evolutionary relationships

• Anatomical Homology– Mammalian forelimbs have same bones

• Vestigial Structures– Traits remain longer than their function does• Humans’ appendix• Whales’ pelvic bone• Penguins’, ostriches’, emus’, et al. wings

Anatomical Homology

Vestigial Structures

Evidence for Evolution II• Shared developmental pathways– Similarity among embryos of same families

• DNA homology– Closer related organisms have greater % homology

• Biogeography– Species geographically share common ancestor

• Fossils– Direct evidence of changing organisms over time

Shared Developmental Pathways(fish, chicken, pig, human)

DNA Homology

DNA Homology II

Biogeography

Fossils

Coevolution

Artificial Selection