Natural Selection Scenarios

Master natural selection with fun scenarios! Understand how traits lead to survival and reproduction.

There are two types of worms: worms that eat at night (nocturnal) and worms that eat during the day (diurnal). The birds eat during the day and seem to be eating ONLY the diurnal worms. The nocturnal worms are in their burrows during that time. Each spring when the worms reproduce, they have about 500 babies but only 100 of these 500 ever become old enough to reproduce. Overpopulation: The worms have 500 babies but only 100 survivePopulation has Variations: There are two types of worms: diurnal and nocturnalStruggle to Survive: The birds eat during the day so nocturnal worms don't get eaten as much.Successful Reproduction: The worms that burrow during the day will more likely survive and reproduce.What worm has natural selection AGAINST it? Diurnal WormsWhat worm has natural selection FOR it? Nocturnal Worms There are three types of polar bears: ones with thick coats, ones with thin coats, and ones with medium coats. It is fall, soon to be winter. The temperatures are dropping rapidly and the bears must be kept warm or they will freeze to death. Many of the bears have had about two cubs each, but due to the extreme temperatures, many mothers only have one cub left. Overpopulation: The bears have two cubs eachPopulation has Variations: There are different types of coatsStruggle to Survive: Winter is coming and they must survive the coldSuccessful Reproduction: The bears with warm enough coats will survive and be able to reproduce laterWhat worm has natural selection AGAINST it? Thin coatsWhat worm has natural selection FOR it? Thick coats In ostriches, there are two types: ones that run fast and those that run slowly. The fast birds can reach up to 40 miles an hour. Jackals love to each ostrich, and they can reach speeds of up to 35-40 miles per hour. A flock of ostrich will lay about 10 eggs (each mother only lays 1), but many rodents break into the eggs and eat the fetus before they hatch. Overpopulation: Many eggs laid, not all survivePopulation has Variations: Fast birds and slow birdsStruggle to Survive: Jackals chase the birds to eat them. Fast birds can run faster than jackals.Successful Reproduction: The faster birds don't get eaten and live to reproduce.What worm has natural selection AGAINST it? Slow birdsWhat worm has natural selection FOR it? Fast birds There are two types of rabbits: those that strictly eat grass and those that strictly eat berries and flowers. A drought occurs one year, and the plants have difficulty producing any extras (like flowers, berries, etc.) They can only try and keep themselves green. The rabbits have babies all year long but many are eaten by foxes or hawks. Due to the drought, many have starved to death. Overpopulation: The rabbits have babies all year but not all survivePopulation has Variations: The bunnies eat different types of thingsStruggle to Survive: There is a drought and significantly less food so many bunnies starve.Successful Reproduction: The bunnies that eat grass, rather than flowers and berries, can find food easier and probably survive longer to reproduce moreWhat worm has natural selection AGAINST it? Flower eating bunniesWhat worm has natural selection FOR it? Grass eating bunnies Bob believes that giraffes have long necks because they have stretched their necks to try and reach food that is high in trees. Since the parent had stretched its neck, it passed the long neck on to its offspring. Ryan believes that giraffes have long necks because the ones with long necks were able to reach the food, and those with short necks could not and died. The long necked giraffes reproduced and soon all the giraffes had long necks. Who thinks like Lamarck? (google Lamarck to read his theory!) BobWho thinks like Darwin? (natural selection guy) Ryan