End Show 15-1 The Puzzle of Life's Diversity Slide 1 of 20 Copyright Pearson Prentice Hall 15-1 The Puzzle of Life's Diversity Evolution is the process

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15-1 The Puzzle of Life's Diversity

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Copyright Pearson Prentice Hall


Evolution is the process by which modern organisms have descended from ancient organisms.

A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

Know the difference:

The fact of evolution.

The Theory of Natural Selection.

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Voyage of the Beagle


In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world.

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During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time.

That hypothesis has become the theory of evolution (aka theory of natural selection).

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Darwin's Observations


• He observed many plants and animals were well suited to the environments they inhabited.

•He was impressed by the ways in which organisms survived and produced offspring.

•Darwin was puzzled by where different species lived and did not live.

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Living Organisms and Fossils

Darwin collected the preserved remains of ancient organisms, called fossils.

Some of those fossils resembled organisms that were still alive.

Others looked completely unlike any creature he had ever seen.

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The Galápagos Islands

Darwin observed that the Galápagos Islands were close together but had very different climates.

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The Journey Home

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

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The Journey Home

Darwin wondered if animals living on different islands had once been members of the same species.

These separate species would have evolved from an original South American ancestor species.

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An Ancient, Changing Earth

Hutton and Lyell 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.

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Lyell's Principles of Geology

Lyell stressed that scientists must explain past events in terms of processes that they can actually observe.

The processes that shaped the Earth millions of years earlier continue in the present.

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This understanding of geology influenced Darwin:

• If the Earth could change over time, life might change as well.

• It would have taken many years for life to change in the way Lyell suggested.

This would have been possible only if the Earth were extremely old.

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Lamarck's Evolution Hypotheses


Jean-Baptiste Lamarck recognized that:

• living things have changed over time.

• all species were descended from other species.

• organisms were adapted to their environments.

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Lamarck 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.

Flaws: Tendency toward perfection

Use and Disuse

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Lamarck’s Evolution


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Evaluating Lamarck's Hypotheses

Lamarck’s hypotheses of evolution are incorrect in several ways.

Lamarck did not know:

• how traits are inherited.

• that an organism’s behavior has no effect on its heritable characteristics.

However, he paved the way for the work of later biologists.

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Population Growth

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

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Publication of On the Origin of Species


He shelved his manuscript for years and told his wife to publish it in case he died.

In 1858, Alfred Wallace sent an essay to Darwin for review. Wallace’s ideas summarized Darwin’s work.

In 1859, Darwin published his book, On the Origin of Species.

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In his book, Darwin:

• proposed a mechanism for evolution called natural selection.

• presented evidence that evolution has been taking place for millions of years—and continues in all living things.

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Inherited Variation and Artificial Selection


Members of each species vary from one another in important ways.

Darwin noted that plant and animal breeders would breed only the largest hogs, the fastest horses, or the cows that produced the most milk.

Darwin termed this process artificial selection.

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Brussels Sprouts

Kohlrabi

Ancestral Species

Kale

Broccoli

Cauliflower

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Evolution by Natural Selection


Darwin compared processes in nature to artificial selection.

By doing so, he developed a scientific hypothesis to explain how evolution occurs.

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The Struggle for Existence

Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources.

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Survival of the Fittest

The ability of an individual to survive and reproduce in its specific environment is fitness.

Darwin proposed that fitness is the result of adaptations.

An adaptation is any inherited characteristic that increases an organism's chance of survival.

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Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection.

In natural selection, the traits being selected contribute to an organism's fitness in its environment.

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Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment.

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Descent With Modification

Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats.

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

Darwin referred to this principle as descent with modification.

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Evidence of Evolution


Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process include:

•the fossil record•geographical distribution•homologous structures•similarities in early development, or embryology.

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The Fossil Record

Darwin saw fossils as a record of the history of life on Earth.

By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time.

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Geographical Distribution

Similar, But Unrelated Species

and

and

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Homologous Body Structures

Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures.

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Homologous Structures

Turtle Alligator Bird Mammal

Ancient, lobe-finned fish

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Not all homologous structures serve important functions.

The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species.

These organs are called vestigial organs.

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Similarities in Embryology

The early stages, or embryos, of many animals with backbones are very similar.

The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.

Chick embryo (LM) Human embryo

Pharyngealpouches

Post-analtail

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Evolutionary Theory

Evolutionary Theory

Scientific advances in many fields of biology, geology, and physics have confirmed and expanded most of Darwin’s hypotheses.

Evolutionary theory continues to change as new data are gathered and new ways of thinking arise.

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End Show 15-1 The Puzzle of Life's Diversity Slide 1 of 20 Copyright Pearson Prentice Hall 15-1 The Puzzle of Life's Diversity Evolution is the process