darwins theory of evolution

plant and animal breeding

Darwin knew that people could breed plants and animals to have useful traits. By selecting which individuals were allowed to reproduce, they could change an organisms traits over several generations. Darwin called this type of change in organisms artificial selection. You can see an example in Figure 7.5. Keeping and breeding pigeons was a popular hobby in Darwins day. Both types of pigeons in the bottom row were bred from the common rock pigeon at the top of the figure.

other scientists

There were three other scientists in particular that influenced Darwin. Their names are Lamarck, Lyell, and Malthus. All three were somewhat older than Darwin, and he was familiar with their writings. Jean Baptiste Lamarck was a French naturalist. He was one of the first scientists to propose that species change over time. In other words, he proposed that evolution occurs. Lamarck also tried to explain how it happens, but he got that part wrong. Lamarck thought that the traits an organism developed during its life time could be passed on to its offspring. He called this the inheritance of acquired characteristics. Charles Lyell was an English geologist. He wrote a famous book called Principles of Geology. Darwin took the book with him on the Beagle. Lyell argued that geological processes such as erosion change Earths surface very gradually. To account for all the changes that had occurred on the planet, Earth must be a lot older than most people believed. Thomas Malthus was an English economist. He wrote a popular essay called On Population. He argued that human populations have the potential to grow faster than the resources they need. When populations get too big, disease and famine occur. These calamities control population size by killing off the weakest people.

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evolution of darwins theory

Heres how Darwin thought through his theory: Like Lamarck, Darwin assumed that species evolve, or change their traits over time. Fossils Darwin found on his voyage helped convince him that evolution occurs. From Lyell, Darwin realized that Earth is very old. This meant that living things had a long time in which to evolve. There was enough time to produce the great diversity of living things that Darwin had observed. From Malthus, Darwin saw that populations could grow faster than their resources. This overproduction of offspring led to a struggle for existence, in Darwins words. In this struggle, only the fittest survive. From Darwins knowledge of artificial selection, he knew how traits can change over time. Breeders artificially select the traits that they find beneficial. These traits become more common over many generations. In nature, Darwin reasoned, individuals with certain traits might be more likely to survive the struggle for existence and have offspring. Their traits would become more common over time. In this case, nature selects the traits that are beneficial. Thats why Darwin called this process natural selection. Darwin used the word fitness to refer to the ability to reproduce and pass traits to the next generation

darwins theory in a nutshell

Darwins theory of evolution by natural selection contains two major ideas: One idea is that evolution happens. Evolution is a change in the inherited traits of organisms over time. Living things have changed as descendants diverged from common ancestors in the past. The other idea is that evolution occurs by natural selection. Natural selection is the process in which living things with beneficial traits produce more offspring. As a result, their traits increase in the population over time.

darwins book

Darwin finally published his theory of evolution by natural selection in 1859. He presented it in his book On the Origin of Species. The book is very detailed and includes a lot of evidence for the theory. Darwins book changed science forever. The theory of evolution by natural selection became the unifying theory of all life science.

darwins finches

Darwin also observed that each of the Galpagos Islands had its own species of finches. The finches on different islands had beaks that differed in size and shape. You can see four examples in Figure 7.4. Darwin investigated further. He found that the different beaks seemed to suit the birds for the food available on their island. For example, finch number 1 in Figure 7.4 used its large, strong beak to crack open and eat big, tough seeds. Finch number 4 had a long, pointed beak that was ideal for eating insects. This seemed reasonable, but how had it come about?

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more influences on darwin

Besides his observations on the Beagle, other influences helped Darwin develop his theory of evolution by natural selection. These included his knowledge of plant and animal breeding and the ideas of other scientists.

voyage of the

How did Darwin come up with the theory of evolution by natural selection? A major influence was an amazing scientific expedition he took on a ship called the Beagle. Darwin was only 22 years old when the ship set sail. The trip lasted for almost five years and circled the globe. Figure 7.2 shows the route the ship took. It set off from Plymouth, England in 1831. It wouldnt return to Plymouth until 1836. Imagine setting out for such an incredible adventure at age 22, and youll understand why the trip had such a big influence on Darwin. Darwins job on the voyage was to observe and collect specimens whenever the ship went ashore. This included plants, animals, rocks, and fossils. Darwin loved nature, so the job was ideal for him. During the long voyage, he made many observations that helped him form his theory of evolution. Some of his most important observations were made on the Galpagos Islands. The 16 Galpagos Islands lie 966 kilometers (about 600 miles) off the west coast of South America. (You can see their location on the map in Figure 7.2.) Some of the animals Darwin observed on the islands were giant tortoises and birds called finches. Watch this video for an excellent introduction to Darwin, his voyage, and the Galpagos:

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giant tortoises

The Galpagos Islands are still famous for their giant tortoises. These gentle giants are found almost nowhere else in the world. Darwin was amazed by their huge size. He was also struck by the variety of shapes of their shells. You can see two examples in Figure 7.3. Each island had tortoises with a different shell shape. The local people even could tell which island a tortoise came from based on the shape of its shell. Darwin wondered how each island came to have its own type of tortoise. He found out that tortoises with dome- shaped shells lived on islands where the plants they ate were abundant and easy to reach. Tortoises with saddle- shaped shells, in contrast, lived on islands that were drier. On those islands, food was often scarce. The saddle shape of their shells allowed tortoises on those islands to reach up and graze on vegetation high above them. This made sense, but how had it happened?

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putting it all together

Darwin spent many years thinking about his own observations and the writings of Lamarck, Lyell, and Malthus. What did it all mean? How did it all fit together? The answer, of course, is the theory of evolution by natural selection.

instructional diagrams

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questions

Darwins theory of evolution includes the idea(s) that

-->  a. inherited traits of living things change over time

b. acquired characteristics can be passed on to offspring

c. artificial selection explains how evolution occurs

d. two of the above

Darwins famous book on evolution is called

a. Adventures on the Beagle

-->  b. On the Origin of Species

c. Evolution by Natural Selection

d. The Theory of Evolution

The book described in question 1 was first published in

a. 1801

b. 1830

-->  c. 1859

d. 1901

The development of Darwins theory was influenced by his

a. observations on the voyage of the Beagle

b. understanding of plant and animal breeding

c. knowledge of the writings of other scientists

-->  d. all of the above

Darwins book On the Origin of Species was first published

-->  a. more than 20 years after Darwin returned from his 5-year voyage

b. as soon as Darwin returned from his voyage on the Beagle

c. when Darwin was only 30 years of age

d. after Darwin died

Onboard the Beagle, Darwin served as the ships

a. doctor

b. captain

-->  c. naturalist

d. navigator

Darwin observed that the environment on different Galpagos Islands was correlated with the shell shape of

a. snails

b. fossils

-->  c. tortoises

d. none of the above

Which statement about the Galpagos Islands is true?

-->  a. There are a total of sixteen Galpagos Islands

b. The Galpagos Islands are located in the Atlantic Ocean

c. The Galpagos Islands were the last stop on Darwins voyage

d. The Galpagos Islands are inhabited only by giant tortoises

What types of specimens did Darwin collect on his voyage?

a. plants

b. animals

c. rocks

-->  d. all of the above

Galpagos Islanders could tell which island a giant tortoise came from based on the

a. size of its feet

b. color of its skin

-->  c. shape of its shell

d. number of its toes

The Galpagos Islands are located off the west coast of

a. North America

b. Africa

c. Australia

-->  d. South America

In Galpagos finches, Darwin noted that beak size and shape seemed to reflect

-->  a. types of available food

b. species of dominant predators

c. kinds of nesting materials

d. sources of fresh water

Darwins job on the Beagle was to observe and collect specimens wherever the ship went ashore.

-->  a. true

b. false

Darwin never observed fossils, so they had no influence on his theory of evolution.

a. true

-->  b. false

Darwin found that the different beaks of Galpagos finches seemed to suit them for different types of

-->  a. true

b. false

Lamarcks ideas about evolution were influenced by Darwins theory of evolution by natural selection.

a. true

-->  b. false

Darwins ideas about natural selection were influenced directly by a book written by Charles Lyell.

a. true

-->  b. false

_The theory of evolution by natural selection explains and unifies all of life science.

-->  a. true

b. false

_All of the giant Galpagos tortoises are now extinct.

a. true

-->  b. false

_Animal breeders produce animals with desired traits by selecting which animals are allowed to

-->  a. true

b. false

_Lamarcks explanation for how evolution occurs was essentially the same as Darwins.

a. true

-->  b. false

_According to Malthus, disease and famine kill off the weakest people when human populations

-->  a. true

b. false

_Darwin knew nothing about the fossil evidence for evolution.

a. true

-->  b. false

_Darwins book on evolution by natural selection was rejected because it contained very little

a. true

-->  b. false

___islands where Darwin made many important observations

a. natural selection

b. Lamarck

-->  c. Galpagos

d. Lyell

e. evolution

f. Malthus

g. Darwin

___scientist who provided geologic evidence that Earth is very old

a. natural selection

b. Lamarck

c. Galpagos

-->  d. Lyell

e. evolution

f. Malthus

g. Darwin

___scientist who argued that populations have the potential to grow faster than the resources they need

a. natural selection

b. Lamarck

c. Galpagos

d. Lyell

e. evolution

-->  f. Malthus

g. Darwin

___change in the inherited traits of organisms over time

a. natural selection

b. Lamarck

c. Galpagos

d. Lyell

-->  e. evolution

f. Malthus

g. Darwin

___scientist who proposed that living things change over time through the inheritance of acquired

a. natural selection

-->  b. Lamarck

c. Galpagos

d. Lyell

e. evolution

f. Malthus

g. Darwin

___process in which living things with beneficial traits produce more offspring so their traits increase

-->  a. natural selection

b. Lamarck

c. Galpagos

d. Lyell

e. evolution

f. Malthus

g. Darwin

___scientist who proposed the theory of evolution by natural selection

a. natural selection

b. Lamarck

c. Galpagos

d. Lyell

e. evolution

f. Malthus

-->  g. Darwin

diagram questions

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