Catalyst: 1.Which of the choices below is an appropriate representation of commensalism? a.+/+c. -/- b.+/-d. +/0 2.How were the activities yesterday connected to evolution? 3.What is the difference between microevolution and macroevolution?

Evolution: A Darwinian View of Life

Overview: Darwin Introduces a Revolutionary Theory A new era of biology began on November 24, 1859 –The day Charles Darwin published: On the Origin of Species by Means of Natural Selection

The Origin of Species –Focused biologists’ attention on the great diversity of organisms Figure 22.1

Darwin made two major points in his book –He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral species –He proposed a mechanism for the evolutionary process, natural selection

The Origin of Species –Shook the deepest roots of Western culture –Challenged a worldview that had been prevalent for centuries

Darwin: from childhood to publication As a boy and into adulthood, Charles Darwin –Had a consuming interest in nature Soon after Darwin received his B.A. degree –He was accepted on board the HMS Beagle, which was about to embark on a voyage around the world

Darwin’s interest in the geographic distribution of species was kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South America Figure 22.5 England EUROPE NORTH AMERICA Galápagos Islands Darwin in 1840, after his return SOUTH AMERICA Cape of Good Hope Cape Horn Tierra del Fuego AFRICA HMS Beagle in port AUSTRALIA Tasmania New Zealand PACIFIC OCEAN Andes ATLANTIC OCEAN

As Darwin reassessed all that he had observed during the voyage of the Beagle He began to perceive adaptation to the environment and the origin of new species as closely related processes Figure 22.6a–c (a) Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. (c) Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. (b) Insect eater. The green warbler finch (Certhidea olivacea) uses its narrow, pointed beak to grasp insects.

Darwin developed two main ideas: 1. Evolution explains life’s unity and diversity 2. Natural selection is a cause of adaptive evolution

The phrase descent with modification –Summarized Darwin’s perception of the unity of life –States that all organisms are related through descent from an ancestor that lived in the remote past

In the Darwinian view, the history of life is like a tree –With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms Figure 22.7 Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Years ago Millions of years ago Deinotherium Mammut Stegodon Mammuthus Platybelodon Barytherium Moeritherium Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa)

Observation #1: For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully Figure 22.8

Observation #2: Nonetheless, populations tend to be stable in size –Except for seasonal fluctuations

Observation #3: Resources are limited

Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

Observation #4: Members of a population vary extensively in their characteristics –No two individuals are exactly alike Figure 22.9

Observation #5: Much of this variation is inheritable

Inference #2: Survival depends in part on inherited traits –Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

Inference #3: This unequal ability of individuals to survive and reproduce –Will lead to a gradual change in a population, with favorable characteristics accumulating over generations

Natural selection can produce an increase over time in the adaptation of organisms to their environment Figure (a)A flower mantid in Malaysia (b)A stick mantid in Africa

Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits, this is called artificial selection Figure Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Flower and stems Broccoli Wild mustard Kohlrabi Stem Kale