Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. As a result, medium sized babies are ones that end up surviving to adulthood.

Which pattern of natural selection does this scenario represent?

Seed cracker birds have either large beaks or small beaks. They do not have medium sized beaks because medium sized beaks do not allow for adequate seed cracking.

Which pattern of natural selection does this scenario represent?

Black rabbits (BB) and white rabbits (WW) are both able to survive because they can camouflage into the white and black rocks in their environment. However, the intermediate gray rabbits (BW) do not survive. This results in white and black rabbits.

Which pattern of natural selection does this scenario represent?

A population of Madagascar hissing cockroaches lives in a woodpile. The cockroaches are eaten by lizards. Because the lizards have small heads, the lizards are unable to eat the very largest cockroaches, and instead prey upon small and medium sized adults. Over time, only the large cockroaches survived.

Which pattern of natural selection does this scenario represent?

Female birds that lay close to the optimum number of eggs have the most surviving offspring. Those that lay fewer or more eggs have lower relative fitness.

Which pattern of natural selection does this scenario represent?

Small lizards have difficulty defending territories, so they end up dying out. Large lizards are more likely to be preyed upon by owls. Over time, only medium sized lizards end up surviving.

Which pattern of natural selection does this scenario represent?

A population of birds with various sized beaks eats seeds. Small seeds can be eaten by birds with small beaks. Larger, thicker seeds can only be eaten by birds with larger, thicker beaks. During a drought, only large think seeds exist so only the large, thick-beaked birds survive.

Which pattern of natural selection does this scenario represent?

Green lizards defend themselves from predators by using their tail length to mimic dangerous snakes. Lizards with shorter tails look less like a snake compared to lizards with longer tails. Over time, the lizards with shorter or medium length tails die out.

Which pattern of natural selection does this scenario represent?

1. The following graphs show the change in crab population from 1950 to 1990.  Which of the following is most likely to have caused the change in the population shown in the graphs?

Students studying the moth population in the woods in Kentucky found the distribution of moth wing color shown in the graph below. The woods contained trees with bark that was mostly black. Two years later a fungus attacked nearly all the trees in the woods and the tree bark changed from black to patches of gray and white.

Which graph shows the probable distribution of moth wing color within the next few years?

Sickle cell anemia is a trait found in central Africa and exhibits co-dominance. If natural selection causes both homozygotes (AA and aa) for sickle cells to die in early childhood, what will eventually happen to the population? 

The graph shows the current length distribution at maturity for a population of fish.  Policy makers will now require that all fish under 60 centimeters (cm) be released back into the water. 

Which graph best predicts how the fish population will change after 10 generations because of this new policy?

Insects that are camouflaged in their environment are less likely to be eaten by birds.  The graph shows the original distribution of body color in a population of one insect species.

The insects live on trees.  A black fungus begins to grow on the trees where the insects live.  Which of the following graphs show the most likely distribution of body color in the insect population after several years of fungus growth?

Most individuals of a certain species of bird have medium-length tails, but tail length ranges within the species from very short to very long.

If a new predator is introduced that prefers birds with medium-length tails, which graph describes the most likely change in the bird population?