Evolution The gradual change in a species over time

Charles Darwin In December 1831, he set sail on the British naval ship HMS Beagle. He was the ship’s naturalist, whose job was to learn as much as he could about the living things he saw on the voyage. His observations on the ship led him to develop one of the most important scientific theories of all time THE THEORY OF EVOLUTION BY NATURAL SELECTION!

Darwin observed plants and animals he had never seen before on his voyage, and wondered why they were so different from the ones he knew of back home in England. These were all different species of organisms, which is a group of similar animals that can mate with each other and produce fertile offspring.

The Journey Continues In 1835, the Beagle reached the Galapagos Islands, which was a group of small islands in the Pacific Ocean off the west coast of South America. Darwin was surprised that many of the plants and animals on the Galapagos Islands were similar to organisms on mainland South America. He also noticed many differences among similar organisms as he traveled from one Galapagos Island to the next.

Darwin’s Finches Darwin noticed that finches (small birds) were very different from one island to the next. The most obvious difference was the sizes of their beaks! He noticed that the beaks size and shape had to do with the food that they ate and the lifestyle they lived. These different beak shapes are an example of an adaptation. Adaptation- a trait that helps organisms survive and reproduce.

This gradual change over time is called EVOLUTION Darwin spent the next 20 years talking with many other scientists to try and understand what he saw on the Galapagos Islands with the finches. He thought that maybe, the species gradually changed over time over many generations, and became better adapted to the new conditions. This gradual change over time is called EVOLUTION

But how does evolution occur? Natural Selection- the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. There are a number of factors that affect natural selection: Overproduction Competition Variations

Overproduction Most species will produce far more offspring than can possibly survive (ex. sea turtles, fish, mice). So many offspring are produced, that there is not enough resources for them to survive, leading to competition.

Competition Since food and other resources are limited, the offspring need to compete with each other to survive. This is usually indirect, not a direct fight between two offspring.

Variations Going back to genetics, members of a species will differ from one to the next in many of their traits. A variation is any difference between individuals of the same species. For example, some birds in a species have bigger beaks than others.

Selection Some variations make certain individuals better adapted to their environment, making them more likely to survive and reproduce. When these individuals reproduce, their offspring can inherit the allele for the helpful trait. The offspring will then be more likely to survive and reproduce and pass on the helpful allele to their offspring. After many generations, more members of the species will have the helpful trait.

Over a long period of time, natural selection can lead to evolution Over a long period of time, natural selection can lead to evolution! Helpful variations gradually accumulate in a species while unfavorable ones disappear, or go extinct.

The Evolution of Giraffes

Only genes are passed from parents to their offspring Only genes are passed from parents to their offspring. Because of this, only traits that are inherited, or controlled by genes, can be acted upon by natural selection.