chapter 16 evidence of evolution (sections 16.1 - 16.5)

www.cengage.com/biology/starr

Albia Dugger • Miami Dade College

Cecie StarrChristine EversLisa Starr

Chapter 16Evidence of Evolution

(Sections 16.1 - 16.5)

http://www.cengage.com/biology/Starr/Concepts8e

16.1 Reflections of a Distant Past

• Events of the ancient past can be explained by studying physical, chemical, and biological processes

• An asteroid impact may have caused a mass extinction 65.5 million years ago

• mass extinction • Simultaneous loss of many lineages from Earth

The K-T Boundary Layer

• A unique rock layer that formed worldwide 65.5 million years ago marks an abrupt transition in the fossil record which implies a mass extinction

16.2 Early Beliefs, Confounding Discoveries

• Expeditions by 19th century naturalists such as Alfred Wallace yielded increasingly detailed observations of nature

• Geology, biogeography, and comparative morphology of organisms led to new ways of thinking about the natural world

Key Terms

• naturalist • Person who observes life from a scientific perspective

• biogeography • Study of patterns in the geographic distribution of species

and communities

• comparative morphology • Study of body plans and structures among groups of

organisms

Biogeography

• Traveling naturalists noted unexplained patterns in the geographic distribution of species

• Plants and animals living in extremely isolated places looked similar to species living on different continents

• Example: Three similar ratite birds – the emu of Australia, rhea of South America, and ostrich of Africa

Similar-Looking, Related Species

Fig. 16.2a, p. 238A Emu, native to Australia


Fig. 16.2c, p. 238

B Rhea, native to South America


Fig. 16.2b, p. 238

C Ostrich, native to Africa


Comparative Morphology

• Naturalists also had trouble classifying organisms that are outwardly very similar, but quite different internally

• Example: the American spiny cactus and African spiny spurge live in similar environments, but are native to different continents – their reproductive parts are very different, so they can’t be as closely related they appear

Similar-Looking, Unrelated Species

Comparative Morphology

• Other organisms that differ greatly in outward appearance may be very similar in underlying structure

• Example: A human arm, a porpoise flipper, an elephant leg, and a bat wing have comparable internal bones

Vestigial Body Parts

• Body parts that have no apparent function, such as leg bones in snakes and tail bones in humans, were also confusing

Fig. 16.4, p. 239

leg bones

coccyx

A Pythons and boa constrictors have tiny leg bones, but snakes do not walk.

B We humans use our legs, but not our coccyx (tail bones).

Vestigial Body Parts

ANIMATION: Comparative pelvic anatomy

To play movie you must be in Slide Show ModePC Users: Please wait for content to load, then click to play

Mac Users: CLICK HERE

Fossils

• Fossils of many animals that had no living representatives were also discovered

• Deeper layers of rock held fossils of simple marine life; layers above them held similar but more complex fossils

• fossil• Remains or traces of an organism that lived in the ancient

past – physical evidence of ancient life

ANIMATION: Comparative anatomys



16.3 A Flurry of New Theories

• In the 1800s, many scholars saw evidence of evolution and realized that life on Earth had changed over time

• 19th century naturalists proposed theories such as catastrophism and inheritance of acquired characteristics in attempts to reconcile traditional beliefs with physical evidence

Key Terms

• catastrophism • Now-abandoned hypothesis of Georges Cuvier, that

catastrophic geologic forces unlike those of the present day shaped Earth’s surface

• evolution• Change in a lineage, or descent with modification

• lineage • Line of descent

Darwin and the HMS Beagle

• In 1831, the 22-year-old Charles Darwin set sail as a naturalist aboard the Beagle, which circumnavigated the globe over a period of five years

• Darwin’s detailed observations of geology, fossils, plants, and animals encountered on this expedition changed the way he thought about evolution

Voyage of the HMS Beagle

Theory of Uniformity

• On his voyage, Darwin read Charles Lyell’s Principles of Geology, which gave him insights into the geologic history of the regions he would encounter on his journey

• theory of uniformity• Idea proposed by Lyell that, over great spans of time,

gradual, everyday geologic processes such as erosion could have sculpted Earth’s current landscape

Charles Darwin

Key Concepts

• Emergence of Evolutionary Thought• Nineteenth-century naturalists started to think about the

global distribution of species• They discovered similarities and differences among major

groups, including those represented as fossils

16.4 Darwin, Wallace, and Natural Selection

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

• Charles Darwin and Alfred Wallace independently came up with a theory of how environments also select traits

Old Bones and Armadillos

• Darwin noticed that fossils of extinct glyptodons from Argentina had many traits in common with modern armadillos

• The idea that they possibly shared an ancestor helped Darwin develop a theory of evolution by natural selection

Ancient Relatives

• A modern armadillo, about a foot long

• Fossil glyptodon, an automobile-sized mammal that lived between 2 million and 15,000 years ago

Competition for Limited Resources

• Thomas Malthus’s wrote that a population tends to grow until it exhausts environmental resources

• As that happens, competition for those resources intensifies among the population’s individuals

• Darwin realized that all populations, not just human ones, must have the capacity to produce more individuals than their environment can support

A Key Insight: Variation in Traits

• Darwin realized that in any population, some individuals have traits that make them better suited to their environment than others – and those traits might enhance the individual’s ability to survive and reproduce (fitness)

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

Key Terms

• fitness • Degree of adaptation to an environment, as measured by

an individual’s relative genetic contribution to future generations

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

Natural Selection

• Darwin considered the way humans select desirable traits in animals by selective breeding (artificial selection)

• Darwin called the process in which environmental pressures result in the differential survival and reproduction of individuals of a population natural selection

• Darwin published On the Origin of Species, which laid out the theory of evolution by natural selection

Key Terms

• artificial selection • Selective breeding of animals by humans

• natural selection • A process in which environmental pressures result in the

differential survival and reproduction of individuals of a population who vary in details of shared, heritable traits

Principles of Natural Selection

Great Minds Think Alike

• Alfred Wallace studied wildlife in the Amazon and Malay Archipelago

• Before Darwin published, Wallace wrote an essay outlining evolution by natural selection—the same theory as Darwin’s

Key Concepts

• A Theory Takes Form• Evidence of evolution, or change in lines of descent, led

Charles Darwin and Alfred Wallace to independently develop a theory of natural selection

• The theory explains how traits that define each species change over time

ANIMATION: Finches of the Galapagos



16.5 Fossils: Evidence of Ancient Life

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

• Most fossils are mineralized bones, teeth, shells, seeds, spores, or other hard body parts

• Trace fossils such as footprints and other impressions, nests, burrows, trails, eggshells, or feces are evidence of an organism’s activities

Process of Fossilization

• Fossilization begins when an organism or its traces become covered by sediments or volcanic ash• After a very long time, pressure and mineralization

transform the remains into rock

• Fossils are found in stacked layers of sedimentary rock• Younger fossils occur in more recent layers, on top of

older fossils in older layers

The Fossil Record

• Fossils are relatively rare, so the fossil record will always be incomplete

• For a fossil of an extinct species to be found, at least one specimen had to be buried before it decomposed or something ate it

• The burial site had to escape destructive geologic events, and it had to be a place accessible enough for us to find

The Ancient Lineage of Whales

• The fossil record holds clues to evolution:• Ancestors of whales probably walked on land• The skull and lower jaw have characteristics similar to

those of ancient carnivorous land animals• With their artiodactyl-like ankle bones, Rodhocetus and

Dorudon were probably offshoots of the artiodactyl-to-modern-whale lineage

Fig. 16.9a, p. 244


Fig. 16.9a, p. 244

A 30-million-year-old 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. 16.9b, p. 244


Fig. 16.9b, p. 244

B Rodhocetus, an ancient whale, lived about 47 million years ago. Its distinctive ankle bones point to a close evolutionary connection to artiodactyls.


Fig. 16.9c, p. 244


Fig. 16.9c, p. 244

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


Fig. 16.9d, p. 244


Fig. 16.9d, p. 244

D Modern cetaceans such as the sperm whale have remnants of a pelvis and leg, but no ankle bones.


Radiometric Dating

• The half-life of a radioisotope allows us to determine the age of rocks and fossils by radiometric dating

• half-life • Characteristic time it takes for half of a quantity of a

radioisotope to decay

• radiometric dating • Method of estimating the age of a rock or fossil by

measuring the content and proportions of a radioisotope and its daughter elements

Radioisotopes

• Radioactive uranium 238 decays into thorium 234, and into other elements until it becomes lead 206• The half-life of uranium 238 to lead 206 is 4.5 billion years

• Recent fossils that still contain carbon can be dated by measuring their carbon 14 content• The half-life of 14C is 5,370 years

Radiometric Dating

• Half-life: The time it takes for half of the atoms in a sample of radioisotope to decay

Radiometric Dating of a Fossil

• 14C in CO2 enters food chains through photosynthesis

• Ratio of 14C to 12C is used to calculate how many half-lives passed since the organism died

Fig. 16.10b, p. 245

B Long ago, trace amounts of 14C and a lot more 12C were incorporated into the tissues of a nautilus. The carbon atoms were part of organic molecules in the nautilus’s food. 12C is stable and 14C decays, but the proportion of the two isotopes in the nautilus’s tissues remained the same. Why? As long as it was alive, the nautilus continued to gain both types of carbon atoms in the same proportions from its food.


Fig. 16.10c, p. 245

C When the nautilus died, it stopped eating, so its body stopped gaining carbon. The 12C atoms already in its tissues were stable, but the 14C atoms (represented as red dots) were decaying into nitrogen atoms. Thus, over time, the amount of 14C decreased relative to the amount of 12C. After 5,370 years, half of the 14C had decayed; after another 5,370 years, half of what was left had decayed, and so on.


Fig. 16.10d, p. 245

D Fossil hunters discover the fossil and measure its 14C and 12C content—the number of atoms of each isotope. The ratio of those numbers can be used to calculate how many half-lives passed since the organism died. For example, if the 14C to 12C ratio is one-eighth of the ratio in living organisms, then three half-lives (½)3 must have passed since the nautilus died. Three half-lives of 14C is 16,110 years.


Fig. 16.10, p. 245

Stepped Art

B Long ago, trace amounts of 14C and a lot more 12C were incorporated into the tissues of a nautilus. The carbon atoms were part of organic molecules in the nautilus’s food. 12C is stable and 14C decays, but the proportion of the two isotopes in the nautilus’s tissues remained the same. Why? As long as it was alive, the nautilus continued to gain both types of carbon atoms in the same proportions from its food.

C When the nautilus died, it stopped eating, so its body stopped gaining carbon. The 12C atoms already in its tissues were stable, but the 14C atoms (represented as red dots) were decaying into nitrogen atoms. Thus, over time, the amount of 14C decreased relative to the amount of 12C. After 5,370 years, half of the 14C had decayed; after another 5,370 years, half of what was left had decayed, and so on.

D Fossil hunters discover the fossil and measure its 14C and 12C content—the number of atoms of each isotope. The ratio of those numbers can be used to calculate how many half-lives passed since the organism died. For example, if the 14C to 12C ratio is one-eighth of the ratio in living organisms, then three half-lives (½)3 must have passed since the nautilus died. Three half-lives of 14C is 16,110 years.

after one half-life

after two half-lives


ANIMATION: Radiometric dating



ANIMATION: Radioisotope decay



ABC Video: New Species of Pterodactyl

chapter 16 evidence of evolution (sections 16.1 - 16.5)

Documents

related speciesfig

similar environments

tiny leg bones

modepc users

playmac users

similar ratite birds

elephant leg

different continentsexample