Chapter 15: Darwin’s Theory of Evolution

15-1 The Puzzle of Life’s Diversity

• Evolution: change over time, process by which modern organisms have descended from ancient organisms.

• Theory: well-supported testable explanation of phenomena that have occurred in the natural world.

Voyage of the Beagle

• Charles Darwin• HMS Beagle- voyage around

the world.• Made many observations

and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

Finches• Studied birds• Noted that they had

differently shaped beaks.• Observed that the

characteristics of many animals and plants varied noticeably among the different islands of the Galapagos.

• Wondered if similar animals on the different islands had once been members of the same species.

15-2 Ideas That Shaped Darwin’s Thinking

• He changed the thinking of many scientists and nonscientists.

• Most people around that time believed that the Earth and all its forms of life had been created only a few thousand years ago and since then nothing has changed. (Darwin didn’t agree)

James Hutton and Charles Lyell

• Recognized 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.

• Examined layers of rock.• Formed over time.• Studied volcanoesgeological features that took awhile to be built up.

Lamarck’s Evolution Hypotheses

• Jean-Baptiste Lamarck• Recognized living things changed over time.• All species were descended from other species.• Organisms were adapted to their environments.• “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.”

Tendency Toward Perfection

• Said all organisms have an innate tendency toward complexity and perfection.

• So they continually change and acquire new features.

• Ex. Ancestors of birds acquired an urge to fly.

Use and Disuse

• Said that organisms could alter the size or shape of particular organs by using their bodies in new ways.

• Ex. If a winged animal did not use its wings then the wings would decrease in size over generations.

Inheritance of Acquired Traits

• Thought that acquired characteristics could be inherited.

• Ex. During lifetime an animal produced longer legs, these new characteristics can be passed on to offspring.

Evaluating Lamarck’s Hypotheses

• Incorrect:• He did not know that an organism’s behavior

has no effect on its heritable characteristics.

Population Growth

• Thomas Malthus• Said that if the human population continued

to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

• Darwin saw this and realized organisms produce far more offspring than can survive and reproduce.

15-3 Darwin Presents His Case

• On the Origin of Species• Darwin’s ideas challenged fundamental scientific

beliefs of his day.• Wallace, published an essay that was close to his

ideas – made Darwin publish his own work.• His book proposed a mechanism for evolution

that he called natural selection.• Said that evolution has been taking lace for

millions of years and continues in all living things.

• http://www.youtube.com/watch?v=910dz5sCb1I&feature=related

Inherited Variation and Artificial Selection

• Darwin’s Observations– Members of each species vary from one another.– Artificial selection: humans selected those

variations to breed to get a desired variation in the offspring.

Evolution by Natural Selection

• Darwin thought that a process like artificial selection worked in nature.

• Struggle for existence: members of each species compete regularly to obtain food, living space, and other necessities of life.

Survival of the Fittest

• Fitness: ability of an individual to survive and reproduce in its environment.

• Adaptation: fitness resulted in adaptation.• Successful adaptations enabled organisms to

become better suited to their environment and thus better able to survive and reproduce.

• Ex. Structural, physiological, behaviors

Survival of the fittest

• Individuals that are better suited to their environment survive and reproduce.

Natural Selection

• Survival of the fittest• Traits are being selected for by nature.• Over time these traits increase in a

population.• These changes increase a species’ fitness in its

environment.

Descent With Modification

• Over time natural selection produces organisms that have different structures, new niches, or occupy different habitats.

• Result: species today look different from their ancestors.

• Each living species has descended, with changes, from other species over time.

• Descent with modification

Common descent

• Descent with modification implies that all living organisms are related to one another.

• Common descent• All species living and extinct

were derived from common ancestors.

• “tree of life” links all living things

Evidence of Evolution

• Darwin said that living things have been evolving on Earth for millions of years.

• Evidence in fossil record.• Geographical distribution of living species.• Homologous structures of living organisms,

and similarities in early development, or embryology.

The Fossil Record

• Compared fossils from older rock layers with fossils from younger layers, scientists could document the fact that life on Earth has changed over time.

Geographic Distribution of Living Species

• Ex. Finches on different islands

• Different ecological conditions made them adapt differently to their environment.

• Ex. Beaver, muskrat, capybara, coypu

Homologous body structures

• Observed that organisms had striking anatomical similarities among body parts.

• Basic bones• Homologous structures: structures that have

different mature forms but develop from the same embryonic tissues.

• Evidence that all four-limbed vertebrates have descended, with modifications, from common ancestors.

Vestigial Organs

• Some homologous structures do not have any function.

• Reduced in size.• Legs of skinks: vestigial organs• Perhaps the presence of a vestigial organ may not

affect an organism’s ability to survive and reproduce.

• Therefore natural selection would not cause the elimination of that organ.

Similarities in Embryology

• Early stages, or embryos, of many animals with backbones are very similar.

• Similar during early stages of development.• Ernst Haeckel drew the embryos to look more

similar than they really are. –but still similar

Summary of Darwin’s Theory

• Individual organisms differ, and some of this variation is heritable.

• Organisms produce more offspring than can survive, and many that do survive do not reproduce.

• Because more organisms are produced than can survive, they compete for limited resources.

• Each unique organism has different advantages and disadvantages in the struggle for existence. Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process of natural selection causes species to change over time.

• Species alive today are descended with modification from ancestral species that lived in the distant past. This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into a single tree of life.

Strengths and Weaknesses of Evolutionary Theory

• Research• 3 evidence observations for Evolution• 3 evidence against Evolution• Your thoughts on the theory of evolution.

• One page long.• Due Monday.

• http://www.youtube.com/watch?v=q76jw0ZB9hA