Chapter 4

Evolution: History and Evidence

Evolution: History and Evidence

• Organic Evolution– Darwin• “Descent with modification”

– Populations change over time.

Pre-Darwinian Theories of Change

• Greek philosophers– Empedocles (495-435 B.C.)– Aristotle (384-322 B.C.)

• Buffon (1707-1788)• Erasmus Darwin(1731-1802)• Lamarck (1744-1829)– Change results from “need”

Voyage of HMS Beagle

• Charles Darwin (1809-1882)– Boarding school– Edinburgh medical school– Christ’s College Cambridge– Nominated by Henslow to serve as

naturalist on HMS Beagle (1831)– On Origin of Species by Means of

Natural Selection (1859)

Figure 4.1 Voyage of the HMS Beagle.

Early Development of Darwin’s Ideas of Evolution

• Geology– Hutton and uniformitarianism• Geological change occurs over hundreds of

millions of years.

– Earth is much older than 6,000 years.– Could not living forms change as well?

Early Development of Darwin’s Ideas of Evolution

• Fossil evidence– South American

fossils

Figure 4.2a The giant sloth.

Early Development of Darwin’s Ideas of Evolution

• Galapagos Islands– Tortoises– Finches

• Adaptive radiation– The formation of

new forms from an ancestral species

Figure 4.3a Galapagos tortoise (Geochelone elephantopus).

Figure 4.4 Adaptive radiation of Galapagos finches.

The Theory of Evolution by Natural Selection

• Other observations– Artificial selection– Thomas Malthus

(1766-1834)

Figure 4.5 Artificial selection in Canis lupis. The 147 breeds of dogs recognized by the AKC originated from artificial selection of wolf ancestors. The grey wolf (a), Shetland Sheep Dog (b), and Irish Wolfhound (c).

(a) (b)

(c)

The Theory of Evolution by Natural Selection

1. High reproductive potential2. Inherited variation exists.3. Constant struggle for limited

resources, many individuals die.4. Adaptive traits become more

common in subsequent generations.

Adaptation

• Occurs when a HERITABLE CHANGE IN PHENOTYPE increases an animal’s chances of SUCCESSFUL REPRODUCTION– Examples?

• Arise as a result of chance mutations

• Perpetuated by natural selection

Figure 4.6 Adaptations of the Arctic Hare (Lepus articus).

Alfred Russel Wallace (1823-1913)

• Theory of evolution similar to Darwin’s

• Published ideas jointly with Darwin• Impetus for Darwin’s publication of On

the Origin of Species by Means of Natural Selection

• Darwin given credit– Years of work – Massive accumulations of evidence

Microevolution, Macroevolution, and Evidence of Macroevolutionary Change

• Microevolution– Change in the frequency of alleles in a

population over time

• Macroevolution– Large-scale changes that result in the

extinction and formation of new species

Biogeography

• Study of the geographic distribution of plants and animals

• Life-forms in different parts of • the world have distinctive

evolutionary histories.• Biogeographers attempt to explain

distribution patterns.

Figure 4.7 Biogeography as evidence of evolutionary change.

Figure 4.8 Biogeographic regions of the world.

Paleontology

• Fossils– Evidence of plants and animals that

existed in the past and have become incorporated into the earth’s crust

• Direct evidence of sequences of appearance and disappearance of organisms

PaleontologyFigure 4.9 Fossils like this trilobite are direct evidence of evolutionary change.

Figure 4.10 The fossil record gives evidence of the horse lineage.

Analogy and Homology

• Convergent evolution– Evolution of superficially similar

structures in unrelated organisms– Similar structures are analogous.

• Homology– Resemblance that occurs because of

common ancestry

Homology—Comparative Anatomy

• Study of the structure of living and fossilized animals and homologies that indicate close relationships

Figure 4.11 Vertebrate forelimbs evolved from an ancestral pattern.

Figure 4.12 Evolution of the vertebrate ear ossicles.

Figure 4.13 Vestigial structures have no apparent function in an animal, but evolved from functioning structures in ancestors.

Homology—Developmental Patterns

• Developmental stages of related animals often retain common features.

• Changes in genes controlling development are usually harmful and eliminated by natural

selection.

Figure 4.14 Early developmental stages of vertebrates are similar.

Homology—Molecular Biology

• Study of nuclear DNA, mitochondrial DNA, ribosomal RNA, and proteins

• Molecules provide direct evidence of change in genes.

• Genetic similarity (degree of relatedness) is reflected in variation in amino acid sequences in proteins and base sequences in DNA.

Interpreting the Evidence: Phylogeny and Common Descent

• Phylogeny– Evolutionary relationships among

species

Phylogenetic Trees

• Show lines of descent

• Branches– Evolutionary

connections

• Nodes– Branch points– Genes, populations,

or species where a change occurs

Modern Synthesis

• Principles of modern genetics combined with Darwinian evolutionary theory

• Chapter 5