Darwin

1. How are these iguanas similar? 2. How are they different?3. Do you think they are related? (Do they share a

common ancestor?)

Darwin’s Voyage

EQ: How did Darwin explain the differences between species on the Galapagos Islands and mainland South America?

Darwin Video Clip

• H:\Science\Evolution\Islands_of_Theory___Charles_Darwin_and_Why_Evolution_Occurs_.asf

Darwin’s 5-Year Voyage

Darwin Reading Guide

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Darwin’s Observations

• What were some observations Darwin made while traveling on the HMS Beagle?– Insects that looked like flowers– Marching ants– Armadillos– Sloths

Darwin’s Questions

• What question did Darwin have about live sloths and sloth bones in Argentina?– Why are only the smaller sloths alive today?– What happened to the giant creatures from the

past?

Species:

A group of similar organisms that can mate with each other and produce fertile offspring.

Similarities & DifferencesSouth American Mainland Galapagos Islands

Cormorants Could fly Could not fly

Iguanas Smaller claws ---Climb trees & eat leaves

Larger claws ---Grip rocks & feed on seaweed

Organisms on the Galapagos Islands

• From his observations, how did Darwin think plants & animals originally came to the Galapagos Islands (from the mainland)?– Blown out to sea during a storm– Drifted on a fallen log

Adaptations• Darwin also observed a type of bird called a

finch. How did the finches look different on each of the islands of the Galapagos?– Strong, wide beaks – for eating seeds– Sharp, needle-like beaks – for eating insects

Beak Advantages• What advantages did the different beaks give

each of the types of finch on their own island?– The ability to eat the food that was most

abundant on their island.

Vocabulary• Adaptation

– A trait that helps an organism survive & reproduce.

• What are some adaptations of these animals?

Darwin’s Explanation

• How did Darwin explain the changes that took place in the animals on the Galapagos Island, making them different from similar organisms on the mainland (and different even than similar organisms on other islands in the Galapagos)?– The species changed (evolved) over many

generations and became better adapted to the new conditions on the islands.

Saddleback Tortoise

Saddleback tortoises have longer necks and legs than their domed buddies, and have a shell shape that lets them extend their heads up higher. These tortoises live on drier islands with scattered plant life that's often hard to reach from the ground. Over many generations the tortoises with "saddleback"-shaped shells were more successful at getting food from higher bushes and trees than dome-shaped tortoises. The tortoises that ate better were also better able to survive and reproduce.

http://teacher.scholastic.com/activities/explorations/adaptation/libraryarticle.asp?ItemID=8&SubjectID=112&categoryID=2

Domed Galapagos Tortoise• These tortoises live on wetter

islands with plenty of vegetation available close to the ground. Domed tortoises have the advantage of being better protected against attacks from predators because they can draw their neck and head into their domed shells and block off their shell entrance with their front legs.

http://teacher.scholastic.com/activities//explorations/adaptation/libraryarticle.asp?ItemID=10&SubjectID=110&categoryID=2&SubjectName=Animals

Vocabulary

• Evolution– The gradual change in a species over time.

• Scientific theory– A well-tested concept that explains a wide range

of observations.