Chapter 22Descent with Modification (Evolution)

• What Evolution?

Change over time in the genetic composition of populations

• What is Natural Selection?

Differential success in reproduction

Ch. 22 - Key Concepts

• 22.1. Darwin challenged traditional views of a young Earth inhabited by unchanging species

• 22.2. Descent with modification by natural selection explains the adaptations of organisms and the diversity of life.

• 22.3. Evolution is supported by an overwhelming amount of scientific evidence

Evolution of insecticide resistance in insect populations

22.9. Artificial selection: diverse vegetables derived from wild mustard

Evolution of drug resistance in HIV

Patients treated with anti-HIV drug 3TC. Percentage of drug-resistant viruses increases and reaches 100% within a few weeks in all cases.

Inquiry 22.13. Can a change in a population’s food source result in evolution by natural selection? (Carroll and Boyd, 1992)See book page 461.

22.2. The context of Darwin’s ideas

Punctuated equilibrium

Trilobite, animals that lived in the seas hundreds of millions of years ago.

Paleontology: The study of fossils (relics or impressions of organisms from the past as mineralized in rock)

22.3. Formation of sedimentary rock and deposition of fossils from different time periods

Strata of sedimentary rock at the Grand Canyon

22.5 The Voyage of HMS Beagle

Galapagos Islands

South America

22.6 Beak variation in Galápagos finches

Diversification of finches on the Galápagos Islands

Title page from The Origin of Species

22.7. “I think ….” In this 1837 sketch, Darwin envisioned the branching pattern of evolution

22.8. Descent with modification:Evolutionary tree of elephant family (based on fossil evidence)

Based on this phylogenetic tree, when did the most recent ancestor shared by Mammuthus (woolly mammoths), Asian elephants and African elephants live?

22.17. Tree thinking: Information provided in an evolutionary tree.Evolutionary tree for tetrapods and their closest living relatives.

• Each branch point represents the common ancestor of the lineage beginning there and to the right of it

• A hatch mark represents a homologous characteristic shared by all the groups to the right of the mark

• If present, what could a horizontal or a vertical axis represent?

Logic of Darwin's theory of natural selection

• OBSERVATION 1: Species can produce more offspring than the environment can support (great reproductive potential).

• OBSERVATION 2: Most populations are normally stable in size over longer periods.

• OBSERVATION 3: Resources are limited.

INFERENCE 1: Production of more individuals than the environment can support (‘struggle for existence’); a fraction

of the offspring survives each generation. • OBSERVATION 4:

Individuals in a population vary both in phenotype and in genotype.

• OBSERVATION 5: This variation is heritable

INFERENCE 2: Survival in the struggle for existence is not random. Those individuals who inherited the most fit characteristics leave more offspring than less fit individuals. INFERENCE 3: This produces a gradual change in population, with favorable characteristics accumulating over the generations.

In evolutionary biology, when we say that one organism has a greater fitness than another organism in the same population, we specifically mean that itA. leaves more viable offspring than others in

that population.

B. competes for resources more successfully than others of its species.

C. utilizes resources more efficiently than other species occupying similar niches.

D. mates more frequently than others of its species.

E. lives longer than others of its species.

In evolutionary biology, when we say that one organism has a greater fitness than another organism in the same population, we specifically mean that itA. leaves more viable offspring than others in

that population.

B. competes for resources more successfully than others of its species.

C. utilizes resources more efficiently than other species occupying similar niches.

D. mates more frequently than others of its species.

E. lives longer than others of its species.

Chapter 22 – Key Concepts

Darwin’s findings challenged traditional views of a young Earth inhabited by unchanging species that were individually created for a particular habitat.

Descent with modification (evolution) by natural selection explains the adaptations of organisms and the unity/diversity of life.

Evolution is supported by an overwhelming amount of scientific evidence.

22.18. Different geographic regions, different mammalian “brands”

Analogous structures due to convergent evolution.

Trace history in one evolutionary branch: The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago.

Evidence points a single founder that arrived several million years ago on the oldest island of Kauai, whose offspring radiated to more than 500 species today!

Where would you expect the most species?

A transitional fossil linking past and present

Vestigial organs

22.16. Anatomical similarities in vertebrate embryos. At some stage in their embryonic development, all vertebrates have a post-anal tail and pharyngeal (throat) pouches.

22.15. Mammalian forelimbs - Homologous structuresAnatomical signs of descent with modification

Limpets (Mollusca) are grazers and live on rocky shores in or near the tidal zone.

Shape of the shell is flat in turbulent, shallow water and more cone-like in quiet, deeper water.

Example question:Which of the following observations helped Darwin shape his concept of descent with modification?

a) Species diversity declines farther from the equator.

b) Fewer species live on islands than on the nearest continents.

c) Birds can be found on islands located farther from the mainland than the bird’s maximum non-stop flight distance.

d) Earthquakes reshape life by causing mass extinctions.

e) South American temperate plants are more similar to the tropical plants of South America than to temperate plants of Europe.

Example question:Which of the following observations helped Darwin shape his concept of descent with modification?

a) Species diversity declines farther from the equator.

b) Fewer species live on islands than on the nearest continents.

c) Birds can be found on islands located farther from the mainland than the bird’s maximum non-stop flight distance.

d) Earthquakes reshape life by causing mass extinctions.

e) South American temperate plants are more similar to the tropical plants of South America than to temperate plants of Europe.