end show slide 1 of 20 copyright pearson prentice hall the puzzle of life's diversity

Copyright Pearson Prentice Hall

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The Puzzle of Life's Diversity


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15-1 The Puzzle of Life's Diversity

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



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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.

Darwin went ashore and collected plant and animal specimens for his collection.


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Darwin's Observations


Organisms were well suited to the environments they inhabited.


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Living Organisms and Fossils

Darwin collected 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

Galápagos Islands were close together but had very different climates.

Organisms varied noticeably among the different islands

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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Ideas That Shaped Darwin's Thinking


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An Ancient, Changing Earth


Hutton and Lyell recognize that the Earth is many millions of years old.

The processes that changed Earth in the past are the same processes that operate in the present.


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Darwin’s understanding of geology:

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

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


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Lamarck's Evolution Hypotheses


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.


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Lamarck's HypothesisA male fiddler crab uses its front claw to ward off predators and to attract mates.


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Lamarck's HypothesisBecause the front claw is used repeatedly, it becomes larger.

This characteristic (large claw) is passed onto its offspring.


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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.


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Population Growth

Population Growth

In 1798, Thomas Malthus noted that babies were being born faster than people were dying.

The only forces that worked against this growth were war, famine, and disease.


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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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Population Growth

When Darwin read Malthus’s work, he realized that this reasoning applied to plants and animals.

If all the offspring of almost any species survived for several generations, they would overrun the world.


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Darwin Presents His Case


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Inherited Variation and Artificial Selection


Members of each species vary from one another

Darwin noted that plant and animal breeders would breed only the best organisms.

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.

He developed a hypothesis called Natural Selection to explain how evolution occurs.


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The Struggle for Existence

High birth rates vs shortages of basic needs would force organisms to compete for food, shelter, etc…


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Survival of the Fittest

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

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


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Individuals with characteristics that are not well suited to their environment either die or leave few offspring.

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

Darwin called this survival of the fittest.


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Over time, natural selection results in changes in the characteristics of a population.

These changes increase a species' fitness in its environment.


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Evidence of Evolution


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

Evidence includes:

●fossil record

●homologous structures

●similarities in embryology


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Similar, But Unrelated Species

and and


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Homologous Structures

Turtle Alligator Bird Mammal

Ancient, lobe-finned fish


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Similarities in Embryology

The embryos of many animals with backbones are very similar.

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


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Summary of Darwin's Theory


Individual organisms differ.

Organisms produce more offspring than can survive.

Organisms compete for limited resources.


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Individuals best suited to their environment survive and reproduce.

These organisms pass their heritable traits to their offspring.

This process of natural selection causes species to change over time.


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Species alive today are descended from ancestors.

This process unites all organisms on Earth into a single tree of life.

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