Natural Selection Image Map

Galapagos Islands - Nature's Laboratory

Galapagos Islands
Age of the Earth
Evidence for Natural Selection
Radioactive Dating
Fossils

The Galapagos islands, a group of about 21 islands, are located about 900 km off the cost of Ecuador. Charles Darwin studied the plants and animals in these islands in 1835. What Darwin saw was a dazzling array of niches and hundreds of species that showed special adaptations for their niche. He studied his notes and drawings for some 25 years before finally publishing his classic book, The Origin of Species.

Satellite view of a volcano on one of the Galapagos Islands. Photo from NASA

Darwin described many niches and their species. Among his most famous objects of study were "Darwin's finches." These were 13 different species of finches found on only one of the islands   that had very specialized beaks that corresponded to the requirements of the food they ate. For example, one species had a large parrot-like beak for cracking seeds.  Another had a delicate beak used to grasp insects. Another had a plier-like beak used to hold twigs in order to probe trees for termites and other wood-boring insects. Clearly, a bird of a given species would have trouble getting enough food if it had the wrong kind of bill for the food it preferred to eat. Observations like this led Darwin to develop his theory of natural selection.

You can learn about the different plants and animals on Galapagos today by clicking here. Research still goes on in these islands. Click here.

Darwin's ideas have gained strength over the subsequent decades of scientific research. Since then, all  that we have learned about geology, genetics, and comparative anatomy and physiology in plants and animals has only served to add further weight to the logic of Darwin's insights.

How Scientists Know The Earth Is Billions of Years Old

Scientists say 
"seeing is believing."

Non-scientists say
"believing is seeing."

Most scientists believe that  the earth is about 4 billion years old, and that the universe is much older than that.

Clearly, it would take a VERY long time for natural selection forces to favor emergence of species that are fitted for the kind of environment they live in. The evidence for the age of the earth includes:

  • The earth originally had only one continent that broke apart letting the pieces drift away from each other to create today's continents (notice for example how Africa seems to fit into South America).  This notion is supported by matching radioactivity, magnetic fields, minerals, and rock formations in the pieces of continents. Given the rate at which continents move today, all this would take millions of years to occur. 

  • Deposits of fossils from different life forms appear in geological sediments and earth layers that would take millions of years to form from erosion and deposits of dust. Fossils are formed from sediments in  lakes and marshes. Successive layers containing different fossils accumulate over thousands of years. Later, erosion can scrape or carve canyons to reveal the layers. Remains of ancient human species are found deep in layers of Olduvai Gorge in Africa. Radioactive dating indicates that these layers are many millions of years old.

  • Radioactive dating (see next page) shows numerous extinct plants and animals that lived millions of years ago. Fossils of these life forms indicate that they became extinct at different times, separated by millions of years. 

  • Numerous transitional forms of life have been found among fossils. Examples: lung-breathing fishes with primitive forelimbs, extinct whales with hind limbs, bird-like dinosaurs, humanoid skulls with smaller brain capacity than today's humans.

The Ichthyosaur

An artist's depiction of the dolphin-like dinosaur, Ichthyosaurus.  This fish-lizard fed on fish and cephalopods.  It was mammal-like in that it gave birth to live young.

  • Transitional forms are not an absolute requirement. Mutations in a few key genes can produce dramatic changes in life form in one generation. See our Story Time for the Populations unit.

 

 

 

 

Introduction | Why It Matters | How We Find Out | What We Know | Story Time
Common Hazards | Activities | Self-Study Game | Teachers Pages | Standards (TEKS)


Peer Curriculum | Ecosystems Home Page | Communication Exercises
Copyright 2001-2003
Web Site Privacy Statement