Evidence of Evolution Chapter 11. 11.1 Impacts/Issues Reflections of a Distant Past Events of the ancient past can be explained by the same physical,

Evidence of Evolution

Chapter 11

11.1 Impacts/IssuesReflections of a Distant Past

Events of the ancient past can be explained by the same physical, chemical, and biological processes that operate in today’s world

From Evidence to Inference

Scientists infer from evidence that an asteroid impact near the Yucatán 65 million years ago caused the mass extinction of dinosaurs

Mass extinction • Simultaneous loss of many lineages from Earth

From Evidence to Inference

Barringer crater, Arizona

Pioneers of Biogeography

Late 1800s: Charles Darwin, Alfred Wallace and other naturalists observed patterns in where species live, how they might be related, and how natural forces might shape life

Biogeography • Study of patterns in the geographic distribution of

species and communities

Biogeography

Wallace and Darwin thought similarities in birds on different continents might indicate a common ancestor

Biogeography

Some plants that lived in similar climates on different continents had similar features, but were not closely related

Comparative Morphology

Naturalists studying body plans were confused by vestigial body parts with no apparent function

Comparative morphology • Scientific study of body plans and structures

among groups of organisms

Vestigial Body Parts

Geology

Identical rock layers in different parts of the world, sequences of similar fossils, and fossils of giant animals with no living representatives also puzzled early naturalists

Confusing Discoveries

Taken as a whole, findings from biogeography, comparative morphology, and geology did not fit with prevailing beliefs of the 19th century

Increasingly extensive observations of nature led to new ways of thinking about the natural world

Comparative pelvic anatomy

11.3 A Flurry of New Theories

Nineteenth-century naturalists tried to explain the accumulating evidence of evolution

Georges Cuvier proposed that catastrophic geologic forces unlike those of the present day shaped Earth’s surface (catastrophism)

Jean-Baptiste Lamarck proposed that changes in an animal over its lifetime were inherited

Evolution

Naturalists suspected that environmental factors affected affect a species’ traits over time, causing changes in a line of descent

Evolution • Change in a line of descent (in a line from an

ancestor)

Voyage of the Beagle

1831: Charles Darwin set out as a naturalist on a five-year voyage aboard the Beagle

He found many unusual fossils and observed animals living in many different environments

Darwin and the Voyage of the Beagle

Lyell’s Theory of Uniformity

Darwin was influenced by Charles Lyell’s Principles of Geology, which set forth the theory of uniformity – in contrast to catastrophism

Theory of uniformity • Idea that gradual repetitive processes occurring

over long time spans shaped Earth’s surface

Shared Traits

Darwin collected fossils of extinct glyptodons, which shared traits with modern armadillos

Limited Resources

Thomas Malthus observed that:• A population tends to grow until it begins to

exhaust environmental resources—food, shelter from predators, etc

• When resources become scarce, individuals must compete for them

Darwin applied these ideas to the species he had observed on his voyage

Fitness

Darwin realized that in any population, some individuals have traits that make them better suited to the environment than others, and therefore more likely to survive and reproduce

Fitness • The degree of adaptation to an environment, as

measured by an individual’s relative genetic contribution to future generations

Adaptation

Adaptive traits that impart greater fitness to an individual become more common in a population over generations, compared with less competitive forms

Adaptation (adaptive trait) • A heritable trait that enhances an individual’s

fitness

Natural Selection

Darwin concluded that the process of natural selection, through variations in fitness and adaptation, is a driving force of evolution

Natural selection • Differential survival and reproduction of

individuals of a population that vary in the details of shared, heritable traits

Great Minds Think Alike

Alfred Wallace, the “father of biogeography”, proposed the theory of natural selection in 1858, at the same time as Darwin

Darwin published On the Origin of Species the following year, in which he described descent with modification, or evolution

Alfred Wallace

The codiscoverer of natural selection

Principles of Natural Selection

The Galapagos Islands

11.4 About Fossils

Fossils• Physical evidence of organisms from the past• Hard fossils include mineralized bones, teeth,

shells, spores and other hard body parts• Trace fossils include footprints, nests, trails, feces

and other evidence of activities

Fig. 11-7a, p. 202

A A 30-million-year-old fossil of Elomeryx. This small terrestrial mammal was a member of the same artiodactyl group that gave rise to hippopotamuses, pigs, deer, sheep, cows, and whales.

Fig. 11-7b, p. 202

B Rodhocetus, an ancient whale, lived about 47 million years ago. Its distinctive ankle bones point to a close evolutionary connection to artiodactyls. Inset: compare a Rodhocetus ankle bone (left) with that of a modern artiodactyl, a pronghorn antelope (right).

Fig. 11-7c, p. 202

C Dorudonatrox, an ancient whale that lived about 37 million years ago. Its artiodactyl-like ankle bones (left) were much too small to have supported the weight of its huge body on land, so this mammal had to be fully aquatic.

11.5 Putting Time Into Perspective

Transitions in the fossil record, found in characteristic layers of sedimentary rock, became boundaries for great intervals of the geologic time scale

Geologic time scale • Chronology of Earth history• Correlates with evolutionary events

Drifting Continents, Changing Seas

Theory of continental drift• Earth’s continents were once part of a single

supercontinent that split up and drifted apart• Explains how the same types of fossils can occur

on both sides of an ocean

Pangea • Supercontinent that formed about 237 million

years ago and broke up about 152 million year ago

Plate Tectonics: A Mechanism of Continental Drift

Theory of plate tectonics • Earth’s outer layer of rock is cracked into plates• Slow movement rafts continents to new positions

over geologic time• Where plates spread apart, molten rock wells up

from deep inside the Earth and solidifies• Where plates collide, one slides under the other

and is destroyed

Plate Tectonics

Gondwana

Certain fossils of ferns and reptiles that predate Pangea are found in similar rock layers in Africa, India, South America, and Australia – evidence of an even earlier supercontinent

Gondwana • Supercontinent that formed more than 500 million

years ago

Impacts on Evolution

Evidence suggests that supercontinents have formed and broken up at least five times

The resulting changes in the Earth’s surface, atmosphere, waters and climates have had profound impacts on evolution

11.6 Similarities in Body Form and Function

Similarities in structure of body parts are often evidence of a common ancestor

Homologous structures • Similar body parts that reflect shared ancestry• May be used for different purposes in different

groups, but the same genes direct their development

Morphological Divergence

A body part that appears very different in appearance may be quite similar in underlying aspects of form – evidence of shared ancestry

Morphological divergence • Evolutionary pattern in which a body part of an

ancestor changes in its descendants (homologous structures)

Fig. 11-12, p. 208

pterosaur

chicken

penguin

stem reptileporpoise

bat

human

elephant

Morphological Divergence Among Vertebrate Forelimbs

Morphological Convergence

Some body parts look alike in different lineages, but did not evolve in a common ancestor

Analogous structures• Similar structures that evolved separately in

different lineages

Morphological convergence • Evolutionary pattern in which similar body parts

evolve separately in different lineage

Morphological Convergence

Fig. 11-13d, p. 209

Insects Bats Humans Crocodiles Birds

wings wings

wings

limbs with 5 digits

Comparative Embryology

Embryos of related species tend to develop in similar ways

Similarities in patterns of embryonic development are the result of master genes (homeotic genes) that have been conserved over evolutionary time

Comparative Embryology

Fig. 11-14a, p. 210

Fig. 11-14b, p. 210

Fig. 11-14c, p. 210

Fig. 11-14d, p. 210

Fig. 11-14e, p. 210

11.7 Biochemical Similarities

Each lineage has unique characters that are a mixture of ancestral and novel traits, including biochemical features such as the nucleotide sequence of DNA

We can discover and clarify evolutionary relationships through comparisons of nucleic acid and protein sequences