DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE CHAPTER 22 DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE

EVOLUTION Evolution is defined as change over time in the genetic composition of a population (not an individual) Most attention given to Charles Darwin’s On the Origin of Species by Means of Natural Selection (November 24, 1859)

CONCEPT 22.1: Pre-Darwinian Views A. Creationism (Scala Naturae) Aristotle’s philosophy Aristotle opposed any concept of evolution Viewed species as fixed and unchanging All living forms could be arranged on a ladder of increasing complexity with each perfect, permanent species having its own rung Strict belief in the Book of Genesis and creation

B. Natural Theology Viewed the adaptations of organisms as evidence that the Creator had designed each species for a purpose Major follower—Carolus Linnaeus (1707-1778) --developed hierarchy of taxonomic categories based morphology and anatomy --did not believe in evolution --taxonomic system became the focal point of Darwin’s arguments for evolution

C. Catastrophism Georges Cuvier, French anatomist and paleontologist and father of paleontology (study of fossils) Based on fossils found in sedimentary rock strata Idea that the boundaries between strata were due to local catastrophic events (fires, floods, volcano eruptions, droughts) that destroyed the species then present

Cuvier proposed the theory of catastrophism to reconcile fossil evidence and his anti-evolutionary background Proposed that catastrophes were localized and regions were repopulated by species immigrating from unaffected areas Opposed idea of gradual evolutionary change

D. Gradualism James Hutton, geologist Change is cumulative product of slow continuous natural processes identical to those currently operating Competitive with Cuvier’s theory

E. Uniformitarianism Charles Lyell Expansion on gradualism Geological processes had not changed throughout Earth’s history

F. Darwin was strongly influenced by Gradualism and Uniformitarianism and reasoned that: Earth must be older than 6000 years. Slow and subtle processes can act on living organisms producing substantial change over a long period of time.

G. Lamarckism Jean Baptiste Lamarck (1744-1829) Mechanism: 1. Use and Disuse --body organs used become stronger/larger --those not used deteriorated 2. Inheritance of Acquired Characteristics --changes acquired during a lifetime are passed on to offspring

Lamarck

II. Concept 22.2: Charles Darwin A. The Voyage of the Beagle Sailed from England in December of 1831 to chart South American coastline Darwin Noted: 1. Geographical distribution of species 2. On the Galapagos Islands he collected several different kinds of finches that were similar but seem to be different species

Voyage of the Beagle (December 1831-October 1836)

B. The Book Darwin perceived the origin of new species and adaptation as closely related processes Formulated theory by early 1840’s 1844 wrote essay on origin of species and natural selection but did not publish June 1858 received Alfred Wallace’s manuscript on evolution and natural selection

Wallace

5. Both papers (Darwin and Wallace) presented by Lyell to Linnaean Society of London on July 1, 1858 6. Darwin published Origin of the Species in 1859 7. Two main ideas of the book: a. Species evolved from ancestral species; not specially created b. Mechanism for evolutionary change— natural selection

C. Principle of Common Descent In the 1st edition, he used term “descent with modification” instead of evolution. Modifications occur as organisms moved into new habitats or as habitats changed Viewed history of life as a tree with most branches evolutionary dead ends Common ancestors at each fork

Phylogenetic Tree

Logic of Darwin’s Theory of Natural Selection All species have potential fertility to show exponential growth in a population if all reproduced successfully. Populations tend to remain stable in size, except for seasonal fluctuations. Resources are limited. Individuals of population vary extensively. Much of this variation is heritable.

Three conclusions: Production of more organisms than can survive leads to a struggle for survival. Survival isn’t random, but depends on heredity. Unequal ability to survive and reproduce will lead to gradual change in a population with favorable characteristics accumulating over generations.

D. Natural Selection 1. Natural selection is the differential success in reproduction that results from the interaction between individuals that vary in heritable traits and their environment. 2. Thomas Robert Malthus’s Essay on the Principles of Population (1798) outlined a “struggle for existence” and heavily influenced Darwin’s views on “over reproduction.” 3. Natural selection is made possible by: a. Variation b. Over reproduction

4. Important Facts About Natural Selection: A population (group of interbreeding individuals of the same species in the same geographic area) is the smallest unit that can evolve. Natural selection can amplify or diminish only heritable variations. Natural selection is always operating, but which traits are favored depends on the environment. 5. Example of Natural Selection: antibiotic resistance in bacteria

III. Concept 22.3: Scientific Evidence to Support Evolution 1. Artificial Selection Striking differences can occur in a very short time if one selects which organisms reproduce. 2. Biogeography Geographical distribution of species Pangea Endemic species

3. Fossil Record Missing links gradually being filled in Shows chronological appearance of vertebrates (fish, amphibians, reptiles, birds, mammals)

Artificial Selection

4. Taxonomy Linnaeus’ taxonomic scheme reflected the genealogy of the tree of life 5. Comparative Anatomy a. Anatomical similarities between species in same taxonomic group show evidence of common descent b. Based on homologous and vestigial structures

homologous structures-represent variations on a structural theme that was present in their common ancestor -Ex: skeleton elements of mammalian forelimbs vestigial organs-remnants of structures that served important functions in the organism’s ancestors -Ex: pelvic and leg bones in snakes; human appendix

Homologous Structures

convergent evolution—refers to the development of structures which have a similar function but develop differently and appear unrelated Leads to analogous structures meaning they have similar functions but not common ancestry Ex: sugar glider and flying squirrel

6. Comparative Embryology Defined as the comparison of early stages of animal development Closely related organisms go through similar stages Ex: all vertebrate embryos have pharyngeal pouches and a tail at some time “Ontogeny recapitulates phylogeny.” Embryonic development (ontogeny) is a replay of the evolutionary history of the species (phylogeny).

Comparative Embryology

Evolutionary tree Evolutionary trees are diagrams that reflect evolutionary relationships among groups of organisms

7. Molecular Biology Hereditary background is reflected in genes and protein products. Since the genetic code is shared by all organisms, it is likely that all species descended from a common ancestor Closer the relationship, the higher the percentage of common DNA.

Molecular Biology

You should now be able to: Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace Describe Lamarck’s theories, and explain why they have been rejected Explain what Darwin meant by “descent with modification” List and explain Darwin’s four observations and two inferences

Explain why an individual organism cannot evolve Describe at least four lines of evidence for evolution by natural selection