Chapter 15Darwin’s Theory

of Evolution

15-1 The Puzzle of Life’s Diversity

The variety of organisms is called biological diversity. How did all these different organisms arise? How are they related?

- Evolution = change over time

- Theory of evolution = a collection of scientific facts, observations and hypotheses

Voyage of the Beagle

- Charles Darwin – made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

- 1831 – He sailed on the HMS Beagle around the world

- Observed & collected plant and animal specimens

Darwin’s Voyage

Darwin’s Observations

- He saw variety in traits, method of reproducing, where they live

- He saw fossils and compared to current living organisms in area

- Galápagos Islands – 1000 km west of S. America

- islands had different climates and slightly different organisms

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shellHoodFloreana

Santa Fe

Santa Cruz

James

Marchena

Fernandina

Isabela

Tower

Darwin observed that the characteristics of many animals and plants varied noticeably among the different Galápagos islands

Giant Tortoises of the Galápagos Islands

The Journey Home

Galapagos organisms

Galapagos tortoise

Frigate bird

Marine Iguana

Albatross

15-2 Ideas That Shaped Darwin’s Thinking

An Ancient, Changing Earth

• Hutton and Lyell (geologists) helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.

15-2 Ideas That Shaped Darwin’s Thinking

Lamarck’s Evolution Hypothesis

- Jean-Baptiste Lamarck ( French naturalist) proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species.

- Organisms have tendency towards perfection.

- Organisms can alter traits.

- New traits can be passed to offspring.

- Ex: If you lift weights to build muscle, your children will be born with big muscles.

- This theory has been disproved by many experiments and observations.

Figure 15–7 Lamarck’s Theory of Evolution

1. Male uses small claw to attracts mates and wards off predators.

2. Front claw becomes larger through use.

3. The acquired characteristic, a large claw, is passed to offspring.

Population Growth

• Thomas Malthus (economist) reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

15-3 Darwin Presents His Case

- Darwin discovered that the Galápagos Islands were home to species that are found nowhere else, but similar to organisms from S. America.

Publication of On the Origin of Species

- Darwin proposed a mechanism for evolution called natural selection in the book On the Origin of Species 1859

Evolution by Natural Selection

- Struggle for existence = Darwin observed high birth rates and a shortage of basic needs cause competition

- Fitness = the ability of an individual to survival and reproduce in its environment

- Adaptation = an inherited characteristic that increases an organism’s chance of survival

1. structural = porcupine’s sharp quills

2. physiological = the way a plant does photosynthesis

3. behavioral = how animals live and hunt in groups

- Process of survival of the fittest:

1. Individuals in a population compete for resources

2. Those with characteristics best suited to the environment survive and reproduce… pass on the beneficial characteristics

3. Over many generations, the beneficial characteristics appear in more members

- Ex: Peppered moths of Manchester

- Common descent – principle that all species, living and extinct, were derived from common ancestors

Evidence of Evolution

- Fossil record – fossils from deeper rock layers are older than fossils from shallower layers

- Geographic distribution of living species – Darwin saw many different species of finches in Galápagos Islands… descended with modification from a common mainland ancestor

Figure 15–14 Geographic Distribution of Living Species

Beaver

NORTH AMERICA

Muskrat

Capybara SOUTH AMERICA

Coypu

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

- Homologous Body Structures – structures that have different mature forms but develop from the same embryonic tissues

- Ex: limbs of reptiles, birds and mammals are constructed from same basic bones

- Scientists can compare how similar the bones are to find degree of relations

Figure 15–15 Homologous Body Structures

Turtle Alligator Bird Mammal

Ancient lobe-finned fish

- Vestigial organs = organs that are reduced in size and resemble homologous organs of other species

- Ex: legs of skinks (lizards), appendix and tailbone of humans, snakes and whales have femur and pelvis bones

VestigialOrgans

- Embryology – The early stages, or embryos, of many animals with backbones are very similar

Concept Map

includes

Evidence of Evolution

Physical remains of organisms

Common ancestral species

Similar genes Similar genes

which is composed of which indicates which implies which implies

The fossil recordGeographic

distribution of living species

Homologous body structures

Similaritiesin early

development

Summary of Darwin’s Theory

- Individuals differ… variation is heritable

- More offspring are born than can survive

- Organisms compete for limited resources

- Organisms best suited for the environment live, reproduce, and pass on traits… natural selection

- Species have descended with modification from common ancestors

Strengths and Weaknesses of Evolutionary Theory

- Questions as to precisely how new species arise

- Uncertainty in how life began