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Natural Selection and Charles Darwin

Charles Darwin is the scientist credited with Theory of Evolution and Natural Selection. He went on a voyage around the world on a ship called H.M.S. Beagle to collect and document plants and animals. In 1831, at the time of Darwin’s voyage, travel was difficult and costly, and people seldom ventured far from their homes. Darwin, however, spent five years exploring the world.  He set foot on many locations in the Southern hemisphere.  As he traveled from place to place, Darwin was surprised, not by the differences between species, but by their similarities. He wrote in his journal of the Galapagos Islands, “...there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America, though separated from that continent by an open space of ocean, between 500 and 600 miles in width.”  At this early stage in his life, soon after graduating from college, Darwin was already accumulating evidence and asking questions that would lead to his theory of natural selection.

Darwin visited Argentina and Australia, which had similar grassland ecosystems. Very different animals inhabited those grasslands, and neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands. Darwin posed challenging questions: Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them? Why were there no kangaroos in England? Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive today. Others looked completely unlike any creature he had ever seen. As Darwin studied fossils, new questions arose: Why had so many of these species disappeared? How were they related to living species? Darwin was particularly fascinated by the land tortoises and marine iguanas in the Galápagos. He noticed that the giant tortoises varied in predictable ways from one island to another, and that the shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. So even though they were all giant tortoises, they were a very diverse species. Diversity can be defined as having many different forms or types of species. Basically, it is the degree of genetic variation.

Darwin hypothesized that organisms had a common ancestor, but have changed slowly over time to make them better suited to survive in their environment. Darwin published his research in 1859 in a book called Origin of Species.

Darwin also noticed differences in the Galápagos Finches. The structure of each bird’s beak is an adaptation to the type of food the bird eats. Match each finch to the type of food you think it eats.

Vegetarian tree finches with its short, hooked beak is perfect for tearing open fruit -- eats berries. The Cactus ground finch with its long, pointed, sharp beaks pick at cacti. The small tree finch has narrow, pointed beaks to grasp insects. The medium ground finch has short, thick beaks to crush seeds.

Natural Selection is a gradual process that results in changes in inherited characteristics of a population changing over time. These changes increase a species chance of survival in its environment. Organisms in nature produce more offspring than can survive, and many of those who do not survive do not reproduce. Members of each species have to compete for food, shelter, and other life necessities. Due to genetic variation, each organism is unique, and each has advantages and disadvantages in the struggle to survive and reproduce. Individuals best suited for the environment survive and reproduce most successful.

Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. For natural selection to occur, there are several factors that need to occur. To find out how it works, imagine a population of beetles:

2. Some individuals are more successful at surviving and reproducing than others. In other words, some variations are more favourable than others.More offspring are produced than survive. Since the environment can't support unlimited population growth, individuals have to compete for resources and try to escape predators. This means that not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. This is also known as survival of the fittest.

3. There is heredity. The differences are passed from parent to offspring.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

4. End result: Populations change over time.The more advantageous trait, brown coloration, which allows the beetle to have more offspring, becomes more common in the population. The successful individuals succeed because of the different traits they have inherited and passed on to their offspring. If this process continues, eventually, all individuals in the population will be brown.

1. There are variations within a population.For example, some beetles are green and some are brown.

Let's look at another example:

When copper contaminated the soil surrounding the monkey flowers, the environment changed. What do you think the area will look like in ten years?

And of course there is the classic example of giraffes. Based on the picture below, use your own words to explain how giraffes have evolved through natural selection to have long necks.

What do you think will have over the next ten years? Draw a picture of what the area would look like, and describe it on the lines below.

Artificial selectionLong before Darwin, farmers and breeders were using the idea of selection to cause major changes in the features of their plants and animals over the course of decades. Farmers and breeders allowed only the plants and animals with desirable characteristics to reproduce, causing the evolution of farm stock. This process is called artificial selection because people (instead of nature) select which organisms get to reproduce.

As shown below, farmers have cultivated numerous popular crops from the wild mustard, by artificially selecting for certain attributes.

These common vegetables were cultivated from forms of wild mustard. This is evolution through artificial selection.

There are many different examples of artificial selection. Can you think of any more? Brainstorm with your elbow partner and list some examples below!

Using your own words, and the picture above to help you, describe artificial selection for breeding dogs.