Evidence of Evolution

Chapter 17

Impacts, IssuesMeasuring Time

Evidence of events that happened millions of years ago – such as meteor impacts – lead to inferences about evolution of life on Earth

17.1 Early Beliefs, Confounding Discoveries

Belief systems are influenced by the extent of our knowledge

Beliefs that are inconsistent with systematic observations of the natural world tend to change over time

Naturalists and Biogeography

Aristotle was one of first naturalists – people who observe life from a scientific perspective

In the late 1800s, Alfred Wallace and others were pioneers in biogeography – the study of patterns in the observation of species

Patterns in Biogeography

Comparative Morphology

Comparative morphologists study body plans and structures among groups of organisms • Some organisms are outwardly similar, but

different internally; others differ outwardly, but have similar internal structures

• Some organisms have vestigial parts with no apparent function

Vestigial Body Parts

Fig. 17-3, p. 261

coccyx

limb bud

Geology

Geologists found identical sequences of rock layers in different parts of the world• Different layers held different fossils – evidence

of earlier forms of life

Cumulative findings from biogeography, comparative morphology, and geology led to new ways of thinking about the natural world

Fossils

17.2 A Flurry of New Theories

By the 1800s, many scholars realized that life on Earth had changed over time, and began to think about what could have caused the changes

New Evidence and Old Beliefs

Catastrophism• Georges Cuvier proposed that many species that

once existed became extinct due to catastrophic geological events unlike those known today

Gradualism• Jean-Baptiste Lamarck proposed that individuals

changed in response to their environment, and passed those changes on to their descendents

Reconsidering Old Beliefs

Theory of uniformity• Lyell’s book, Principles of Geology, proposed that

gradual, repetitive geological processes shaped the Earth over great spans of time

• Lyell’s insights shaped Charles Darwin’s thinking during his five-year voyage on the Beagle

Voyage of the Beagle

Darwin observed unusual fossils and diverse species in a range of habitats

Beagle and The Galapagos Islands

17.1-17.2 Key Concepts Emergence of Evolutionary Thought

Long ago, naturalists started to catalog previously unknown species and think about the global distribution of all species

They discovered similarities and differences among major groups, including those represented as fossils in layers of sedimentary rock

17.3 Darwin and Natural Selection

Darwin’s observations of species in different parts of the world helped him understand a driving force of evolution – natural selection

Old Bones and Armadillos

Darwin observed similarities between fossil glyptodons in Argentina and the armadillo

A Key Insight – Variation in Traits

Darwin’s observations:• Populations can produce more individuals than

their environment can support• Some versions of a trait might enhance an

individual’s ability to survive and reproduce in its particular environment

• Example: Finches in the Galapagos Islands

Finches in the Galapagos Islands

Natural Selection

Natural selection• Differential survival and reproduction among

individuals of a population that vary in details of shared, inherited traits

Adaptive trait• Any trait that enhances an individual’s fitness

(ability to survive and reproduce in a particular environment)

Principles of Natural Selection

Table 17-1, p. 265

Stepped Art

17.4 Great Minds Think Alike

Darwin’s insights into evolution were made possible by contributions of scientists who preceded him

Alfred Wallace independently developed the idea of evolution by natural selection

Alfred Wallace

Wallace drew on his own observations of plant and animal species and proposed that natural selection is a driving force of evolution

17.3-17.4 Key Concepts A Theory Takes Form

Evidence of evolution, or changes in lines of descent, gradually accumulated

Charles Darwin and Alfred Wallace independently developed a theory of natural selection to explain how heritable traits that define each species evolve

17.5 About Fossils

Fossils are remnants or traces of organisms that lived in the past

They give us clues about evolutionary relationships

The fossil record will always be incomplete

Fossils

Fossils• Remains of bones, teeth, shells, seeds, spores,

or other body parts

Trace fossils• Evidence of an organism’s activities (nests, trails,

footprints, burrows, bore holes, eggshells, feces)

Fossils

Fig. 17-9a, p. 267

Fig. 17-9b, p. 267

Fig. 17-9c, p. 267

How Do Fossils Form?

Organisms or traces are covered in sediments or volcanic ash

Inorganic compounds dissolved in water slowly replace minerals in bones and hard tissues

Pressure and mineralization transform remains into rocks

Fossil-Containing Sedimentary Rock

The oldest fossils are usually in the deepest layers of sedimentary rocks

The Fossil Record

The fossil record will never be complete• Geologic events obliterated much of it• Slanted toward species with hard parts, dense

populations, wide distribution, long periods of time• Substantial enough to help reconstruct patterns

and trends in the history of life, and establish some lines of descent (lineages)

17.6 Dating Pieces of the Puzzle

Researchers use predictable radioisotope decay to estimate the age of rocks and fossils

Radiometric dating• Reveals the age of a material by determining its

radioisotope and daughter element content

Radioisotopes

Radioisotope• A form of an element with an unstable nucleus• Decays into atoms of another element

• Example: uranium 238 → lead 206

Half-life• The time it takes for half of a radioisotope’s atoms

to decay into a daughter element

Half-Life

Fig. 17-11, p. 268

newly formed rock

parent isotope

after one half-life

after two half-lives

daughter isotope

newly formed rock

parent isotope

daughter isotope

Fig. 17-11, p. 268

Stepped Art

after one half-life

after two half-lives

Animation: Radioisotope decay

Carbon 14 Dating

Animation: Radiometric dating

17.7 A Whale of a Story

New fossil discoveries are continually filling the gaps in our understanding of the ancient history of many lineages

New Links in the Ancient Lineage of Whales

New Links in the Ancient Lineage of Whales

New Links in the Ancient Lineage of Whales

17.5-17.7 Key Concepts Evidence From Fossils

The fossil record offers physical evidence of past changes in lines of descent

We use the property of radioisotope decay to determine the age of rocks and fossils

17.8 Putting Time into Perspective

Geologic time scale• The chronology of Earth’s history• Measured by radiometric dating and fossils in

similar sequences of sedimentary rock layers around the world

The Geologic Time Scale

Fig. 17-14a, p. 270

Fig. 17-14b, p. 271

Animation: Geologic time scale

17.9 Drifting Continents, Changing Seas

For billions of years, slow movements of Earth’s outer layer and catastrophic events have changed the land, atmosphere, and oceans, with profound effects on the evolution of life

Continental Drift

Continental drift• All continents were once part of a supercontinent

– Pangea – that split and drifted apart• Evidence: Magnetic rocks

Plate tectonics• The mechanisms of continental drift• Plate grow from ridges and sink into trenches

Plate Tectonics

Fig. 17-15, p. 272

trench hot spot ridge trench rift

A B C D

A Plumes of molten rock rupture a tectonic plate at what are called “hot spots.” The Hawaiian Archipelago has been forming this way.

B At oceanic ridges, huge plumes of molten rock welling up from Earth’s interior drive the movement of tectonic plates. New crust spreads laterally as it forms on the surface, forcing adjacent tectonic plates away from the ridge and into trenches elsewhere.

C At trenches, the advancing edge of one plate plows under an adjacent plate and buckles it. The Cascades, Andes, and other great coastal mountain ranges formed this way.

D At rifts, continents rupture in their interior as plates slide apart from each other.

Boundaries of Tectonic Plates

San Andreas Fault

Gondwana

Supercontinents continually form and split, altering habitats and influencing evolution

Gondwana• Ancient supercontinent, older than Pangea • Similar fossils and geologic formations in Africa,

India, South America and Australia

The Drifting Continents

Fig. 17-17, p. 273

A 420 mya B 237 mya C 152 mya D 65.5 mya E 14 mya

Fig. 17-17 (top left), p. 273

Fig. 17-17 (top right), p. 273

17.8-17.9 Key Concepts Evidence From Biogeography

Correlating evolutionary theories with geologic history helps explain the distribution of species, past and present

Animation: Comparative pelvic anatomy

Animation: Continental drift

Animation: Finches of the Galapagos

Animation: Geologic forces

Animation: Plate margins

Animation: The Galapagos Islands

ABC video: Creation vs. Evolution

ABC video: Chickens have a new ancestor

ABC video: Indonesian Earthquake

ABC video: Asteroid Menace

Video: Measuring time