Chapter 16 Notes

Darwin’s Theory of Evolution

 

Charles Darwin: Born in England February 2,1809 to a wealthy family.  Darwin attended Oxford University.  He became a naturalist.

 

 Charles Darwin:

 Naturalist

 

 

 

In 1831 Darwin joined the crew of the H.M.S. Beagle for a 5 year voyage.

 

 

What Darwin learned from the voyage:

·      Darwin made numerous observations and collected data that led him to propose a revolutionary hypothesis about the way life changes (evolution).

 

Darwin’s Observations:

1.  Patterns of Diversity

q       So many plants and animals are well suited to whatever environment they inhabit.

q        There are so many ways that organisms survive and produce offspring.

q       Different species live all over the world

Ex. Argentina, Australia, and England have similar grassland ecosystems, yet the animals inhabiting these areas were different.

 

2.  Living Organisms and Fossils

q       Darwin collected remains of preserved  organisms called fossils.

q       Some of the fossils resembled organisms that were still alive and others looked completely unlike any creature he had ever seen.

q       Why had so many of these species disappeared?

3.  The Galapagos Islands

q       Darwin observed that the characteristics of many animals and plants varied noticeably among the different Galapagos Islands.

 

Example:  The tortoises’ shape of the shell corresponded to different habitats. 

The Hood Island tortoise has a long neck and a shell that is curved and open around the neck and legs, allowing the tortoise to reach the sparse vegetation Hood Island.

AW_Galapagos53

 

 The tortoise for Isabela Island has a dome-shaped shell and a shorter neck because the vegetation is more abundant and closer to the ground.

 

 

 

The tortoise from Pinta Island has a shell that is intermediate between these two forms.  The tortoises here were also larger than anywhere else around the world.

 

Another Example:   Flightless Cormorant

·      The only flightless cormorant in the world lives in the Galapagos Islands probable because there are no predators.

 

Example #3: The finches on each island were different their beak shape because of the food source available on each island.

·      Darwin began to wonder if animals living on different islands had once been members of the same species.

 

Example #4: Galapagos Plants undergo the same pressures of the environment.  There are deserts, forests, and lava rock that allow for all kinds of different vegetation.

     Photo of passion flower

 

         

Beliefs about the History of the Earth before Darwin:

·      The earth was roughly 6000 years old.

·      The earth and all species were created at the same time.

·      The earth and all species had not changed since creation.

                                                                                   

What shaped Darwin’s ideas of how things changed?

 

Darwin Returned to England (1836-1859): 

q       Studied the data he collected during the voyage including insects, mollusks, fossils, and plants.

q       Darwin performed selective breeding experiments on pigeons.  (Selective breeding/Artificial Breeding is where the scientist chooses the trait to be passed on to the next generation.)

 

q       Darwin was influenced by the work of several scientists who studied the history of the Earth.

 

1.       James Hutton and Charles Lyell:

q       Helped scientists recognize that Earth is many millions of years old.

q       NOTE: We now know the earth is 4.6 billion years old.

q       Hutton proposed that the geological forces such movement of the sea floor being pushed up to form mountain ranges, rain, heat, wind, and cold (erosion) all operate extremely slowly.

 James Hutton: Geologist

q       Lyell stressed that the processes that shaped the Earth millions of years ago are the same processes that are at work now. 

Examples: Volcanoes and earthquakes

 

 Sir Charles Lyell: Geologist

 

q       Darwin could relate to this because he observed a volcano and observed where an earthquake had caused the sea floor to raise.

q       This influenced Darwin to ask, “If the Earth could change over time, might life change as well?”

q       Darwin realized that it would take many, many years for life to change.

 

 

 

2.       Jean-Baptiste Lamarck:

Jean-Baptiste Lamarck: Naturalist

  

q       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.

 

Example:  The giraffe would stretch its neck to reach the higher food.  This stretching caused the neck to get longer.  The longer necks of those who stretched could be passed on to the next generation.

 

Another Example:  The male fiddler crab uses its small front claw to ward off predators and attract a mate.  Because it uses the front claw repeatedly, it becomes larger.

 

§      The hypothesis proposed by Lamarck  was found to be incorrect.  He did not understand how traits are passed on and that an organism’s behavior does not shape its inheritance of characteristics.

 

§      Lamarck was however the first to figure out that organisms are adapted to their environments. 

 

3.       Thomas Malthus:

 Thomas Malthus: Economist

  

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

q       This did not occur in people, maple trees, or oysters like Malthus suggested.  However, a great number of organisms did die. 

q       This influenced Darwin to ask, “Why did the majority of the offspring die, but a few survived and succeeded in reproducing?”

q       This became the central question in Darwin’s explanation of evolutionary change.

 

4.       Alfred Wallace:

  Alfred Wallace: Naturalist

 

q       Wallace writes to Darwin speculating on evolution by natural selection (which was also what Darwin had proposed), based on his studies of the distribution of plants and animals.  Darwin presented Wallace’s essay to the Linnaean Society.