EVOLUTION NATURAL SELECTION

How Does Evolution Work? On his journey with the HMS Beagle, Darwin studied many different living organisms. His research revealed that species changed over time. Back at home in England, Darwin knew that dogs could be bred for certain traits the breeders wanted. Traits are features passed on from parents to offspring, like your eye color! This is called artificial selection and farmers still use it today! What trait did breeders select for in bulldogs?

2. Darwin realized for most organisms, nature was doing the selecting 2. Darwin realized for most organisms, nature was doing the selecting. The organisms that were best suited to an environment were the ones most likely to survive and pass on their traits. In a snowy environment like the Artic, white foxes are more successful because they are camouflaged. But in the woods, a brown fox is more successful. The process where organisms that are best suited for their environment survive and go on to produce more offspring is called natural selection.

Natural selection point 1: Variation 3. Natural selection as a process has 4 key points. First is variation. The members of a species are all similar but they are not exactly alike. Traits are passed on to you through DNA from your parents. Some of the traits passed are on by accidental changes called mutations. If the mutation is helpful the trait will help the organism to survive, and it can be passed on to its offspring. Like the panda’s thumb. The extra big wrist bone helped the panda eat bamboo, and pandas with plenty of food were most likely to survive, so pandas with big wrist bones survived and passed on that trait. So part 1 of natural selection is that you can inherit variation.

OVERPRODUCTION 4. A second point about natural selection is that organisms overproduce, which means they produce more offspring than can survive. Fish can lay millions of little eggs. Many of the eggs never hatch, some might be eaten by a predator, and others might not get the nourishment they need to survive.

5. COMPETITION A third key point is that overproduction leads to competition. Organisms have to have food, water, and shelter to survive. Organisms also have to find mates in order to reproduce. Since more organisms are born than there are resources available, organisms have to compete for the available resources. Why would this fish be a “stronger competitor?”

6. Natural selection The fourth key point is that something in the environment “selects” which organisms are best fit. Sometimes it’s a predator, sometimes it’s mating preferences, but it is nature that is selecting who survives and has offspring. Sometimes in specific patterns like towards being “stronger” or “faster.” The important thing is that the population changes over time. Sometimes the organisms change so much they are different species. This is called speciation. What environment would produce the pattern at the end “stabilizing selection?

NATURAL SELECTION IN ACTION Click on one of the below links to watch an animation of natural selection in peppered moths. The selecting force here was both birds choosing which moths to eat and the industrial pollution staining the trees so that different moths were camouflaged. Click to play the peppered moth game! http://www.recercaenaccio.cat/agaur_reac/AppJava/en/interactiu/20091218-betularia.jsp/ Click to watch the interactive tutorial http://www.techapps.net/interactives/mothproject.htm

SUMMARY SLIDE Natural Selection is the process where organisms best suited for their environment survive and then go on to produce more offspring. Variation exists in populations. This variation can be caused by random mutations and can be passed down from parents to offspring. Overproduction - There are more organisms born than can live to survive. Limited resources in the environment causes Competition for food, water, shelter, and mates. This results in Survival of the Fittest - those organisms with the most adaptive traits live longer and reproduce more. This causes the population to change to be more like the most “fit” organisms – EVOLUTION by NATURAL SELECTION.