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Darwin’s Theory of Evolution

Chapter 16

16.1 Darwin’s Voyage of Discovery

Charles Darwin Born Feb 12, 1809 The first person to publish convincing evidence that

species evolve, and propose a reasonable mechanism explaining how evolution occurs. Modern organisms evolved over long periods of time

through decent from common ancestors.

Science Before Darwin

In Darwin’s time, most people and scientists believed that each species exists, unchanged as it has for all time.

However, views were beginning to change dramatically The Earth had changed along with all living things on Earth

With the discovery of more and more fossils scientists began to propose various mechanisms to explain how these species change over time.

Jean Baptiste Lamarck, in 1809, proposed a hypothesis of the inheritance of acquired characteristics. This hypothesis stated that by use or disuse of a body

part could cause change in that feature within the lifetime of the organism.

These changes would then be passed on to offspring. Lamarck’s hypothesis is now known to be incorrect.

Darwin’s Epic Journey

In 1831, at age 22, Darwin took a position as a naturalist on a voyage of the HMS Beagle. On the Beagle’s 5-year journey it sailed around the

world to map the coast of South America. During the voyage Darwin found evidence that

challenged the belief that species are unchanging.

Observations

Three patterns of biological diversity:1. Species vary globally2. Species vary locally3. Species vary over time

Species Vary Globally

Similar animals live in separate, but similar habitats.

Rheas – South America Ostrich - Africa

Species Vary Locally

Different, yet related species occupied different habitats in the same area.

Isabella Island Hood Island

Species Vary Over Time

Fossils of extinct animals are similar to living species.

Putting it Together

Darwin noticed that the finches on each of the Galápagos islands had differently shaped beaks, and were similar to those in South America.

He spent years researching his ideas after he returned.

He began to wonder if the animals living on the different islands had come from a common ancestor.

16.3 Darwin Presents His Case

In 1858 Darwin published his ideas in the book “On the Origin of Species.”

This book outlined Darwin’s ideas of evolution based on natural selection focusing on three principles: The struggle for existence Variation and Adaptation Survival of the fittest

Struggle for Existence

Though every organism has the potential to produce many offspring, only a limited number of those survive and reproduce.

1 in 1000 survive to adulthood 50% survive past 1 year

Variation and Adaptation

Individuals in a population vary in heritable characteristics Adaptations increase an organism’s ability to survive

and reproduce. Camouflage Mimicry Behaviors

Survival of the Fittest

Fitness is how well an organism can survive and reproduce in its environment. Individuals with a high fitness are well suited for

their environment and are more likely to survive and reproduce.

Individuals with low fitness are not as well suited to their environment therefore will either die or leave few offspring.

Natural Selection

These mechanisms allow for natural selection to occur. Each generation populations continue to change as

more individuals are born with favorable traits for the environment.

It is important to remember that if environmental conditions change faster than a species can adapt to the changes, the species may become extinct.

Example p. 462

16.4 Evidence of Evolution

The Age of the Earth and The Fossil Record

Earth is 4.5 billion years old

Fossils provide the most direct evidence that evolution takes place. Fossils are preserved or mineralized remains or

imprint of an organism that lived long ago.

Fossils provide an actual record of Earth’s past life forms.

Fossils are used to trace the evolution of modern species from extinct species.

Although the fossil record is not, and will never, be complete it presents strong evidence that evolution has taken place.

Paleontologists analyze fossils by dating the rocks and minerals around it.

They can arrange the fossils from oldest to youngest, and in this, orderly patterns of evolution can be seen.

Comparing Anatomy and Embryology

Homologous Structures Similarities in bone structure suggest that all vertebrates share

a common ancestor.

Vestigial structures also provide evidence for evolution. Ex: hind limbs of whales and dolphins

Embryology

At some time in their development all vertebrate embryos have a tail, a notochord, and pharyngeal pouches. Suggesting common ancestry

Genetics and Molecular Evidence

Similarities in gene sequences can be linked to common ancestry.

Today we now know that genes are responsible for inherited traits. Traits become more common in a population because

more individuals in the population carry the alleles for those forms.

Mutations and the recombination of alleles that occurs during sexual reproduction provide endless sources of new variations for natural selection to act upon.

Analyzing Data p.470

Examples of Evolution

Natural Selection at Work

The key lesson scientists have learned about evolution by natural selection is that the environment dictated the direction and amount of change.

Ex: The polar bear’s white fur enables it to hunt successfully in its snowy environment. In a warmer environment, having white fur would no longer be an advantage.

Examples of Natural Selection

Bacteria that cause disease evolve to have resistance to antibiotics. Ex: TB, Staff