Darwin and the Theory of Evolution

Darwin’s Voyage In 1831, Charles Darwin set sail on a five year long voyage on a British Naval ship called the Beagle. Everywhere he went he observed the plants and animals.

H.M.S. Beagle

Darwin’s Voyage

Galapagos Islands When Darwin reached the Galapagos Islands, he found animals very similar to the ones he saw on mainland South America. However, they were a little different.

South America Iguana Galapagos Iguana

South America Finch Galapagos Finch

South America Galapagos Cormorant Cormorant

Animal Differences On the Galapagos, the Cormorants couldn’t fly, the iguanas had long claws, and the beaks of the finches were shaped differently.

Adaptations Darwin realized these were examples of adaptations. Adaptations are traits that help an organism survive and reproduce.

But, how did the animals get these traits???

Darwin’s Theory Darwin thought that the ancestors of these animals lived on the mainland many, many years before. Maybe they had floated on logs or were blown to the Galapagos Islands by a storm.

Theory of Evolution To survive on the islands, the animals had to change to become better adapted to the new conditions. Evolution is the gradual change in a species over time.

How does evolution occur? Darwin wrote a book entitled The Origin of Species that explained how evolution happens.

Natural Selection He said evolution occurs by means of natural selection. Natural selection is where individuals that are better adapted to their environment are more likely to survive and reproduce. It’s like “survival of the fittest.”

What affects natural selection? Darwin wrote in his book that three things affect natural selection: overproduction, competition, and variations.

Overproduction Overproduction means that most species produce far more offspring than could ever survive. Sea turtles, for example, lay over 100 eggs. Why do you think they do this?

Competition Competition means that the offspring will have to compete with one another for such things as food and mates.

Variations Variations are the differences between individuals of the same species. For example, some turtles can swim faster than other turtles after they hatch.

What does it all mean? Those offspring that are born with the traits that are better adapted for their environment will survive more often and will be the ones to have offspring some day.

They will pass those traits to their offspring through their genes and then their offspring will be more likely to have those same traits.

The new offspring will have a better chance of surviving and passing those traits to their own offspring some day. If this goes on and on, generation after generation then…

…this leads to evolution …this leads to evolution. Helpful variations accumulate in a species and unfavorable ones disappear.

Since traits are controlled by genes which are passed from parents to offspring, only traits that are inherited can be acted upon by natural selection.

Here’s an example.

Think about it! Why do you think the shape of the beak of the finches varied from one island to another? Hint: Think about how they use their beaks.

Think about it! Why do you think the cormorants on the Galapagos Islands could not fly? Hint: The cormorants had to get their food from the ocean.

Think about it! Why do you think the iguanas had long claws on the Galapagos? Hint: They climbed on slippery rocks to eat seaweed.

More Evidence Before the industrial revolution in England, peppered moths were white. After factories were built they became black. Why?

Peppered Moths before the Industrial Revolution

Peppered Moths after the Industrial Revolution

The End