Darwin and the Theory of Evolution Link to VS

Darwin’s Voyage In 1831, Charles Darwin (1809–82) 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 the mainland of South America. However, they were a little different.

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

South America Finch Galapagos Finch

South America Galapagos Cormorant Cormorant

South America Iguana Galapagos Iguana Link to VS

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. impt

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. impt

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 sometimes referred to as the “survival of the fittest.” impt

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

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? Link

Sea turtles lay over 100 eggs at one time because the majority of the babies will not survive to adulthood. This helps to ensure the survival of the sea turtle.

Competition Competition means that the offspring will have to strive against another or others to attain a goal or an advantage for such things as food and mates.

Competition is the struggle between organisms that attempt to use the same limited resources. Resources include food, water, and a place to live. Organisms that are better at competing are more likely to get and use the available resources.

Predators (hunters) generally have traits that enhance their ability to capture prey, such as fast speed, keen eyesight, and sharp teeth.

Prey have traits that help them avoid being captured, such as the ability to escape quickly or to hide in the environment. Some prey have fur or skin colors and patterns to help them blend in to their environment. They are camouflaged.

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 (are more likely to survive) 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.

More Evidence Usually we do not even notice these changes because they happen very slowly over many, many years. One example of natural selection is the peppered moth population of Manchester, England. Parts of this information comes from the Georgia GPS edition Coach book.

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

Peppered Moths Peppered moths have variations in wing color. They are called peppered moths because it looks like they are sprinkled with pepper. Some have more white showing than others. These differences among the same species of organism are called variations.

Peppered Moth Patterns

Peppered Moths At one time in Manchester, the white moths with a little black speckling blended in well with the light colored trees in their environment. Birds had difficulty seeing these camouflaged moths, so they tended to survive and reproduce, passing on their trait for coloration.

Peppered Moths before the Industrial Revolution

The Industrial Revolution in England was powered by coal The Industrial Revolution in England was powered by coal. Coal ash and soot polluted the city of Manchester. The soot settled on trees and plants and stayed there. The peppered moths that were more white than black were more easily seen and caught by predators.

Peppered Moths after the Industrial Revolution

Now, the moths that were darker (had less white showing) were less likely to be seen by predators. They survived to reproduce and pass on the gene for dark coloration. Over time, peppered moths became black (dominant gene). Again, where the insects lived affected their coloration. If they don’t adapt, the species dies out.

Because of the variations among peppered moths, the species survived Because of the variations among peppered moths, the species survived. Had they all looked identical (meaning no variations among peppered moths), all of the moths might have been eaten. The entire species might have disappeared. If a species cannot adapt to changes in their environment, the species dies out.

Darwin’s theory of natural selection states that helpful variations (or adaptations) are passed from generation to generation. Over time, the adaptation becomes more common in that species. Natural selection can result in small changes in a species over time. It can also result in very large changes and in the formation of new species from existing species.

Horses are a classic example of the development of a new species when the environment changed. Modern horses and zebras eat grass. They are descended from smaller animals that ate a variety of plants. The environment where they lived changed to be a grassland. Grass is tough and hard to chew. The ancestors of modern horses developed teeth that are not worn down by eating grass.

The ability to run fast is also useful in a grassland The ability to run fast is also useful in a grassland. Animals with longer legs were better adapted to running in the tall grass. Over time, horses and zebras grew larger, with longer legs. There are some other changes that we will talk about when we study the fossil record.