GED Science Evolution and Natural Selection Summary

Natural selection needs variation (differences) in traits, and those traits must be inherited. Individuals with helpful traits survive and reproduce more, so those traits become more common over generations.

Wrong choices

• all be exactly the same: If every individual were identical, no trait could be favored over another.
• never compete for food or mates: Competition for limited resources is part of what drives selection.
• choose which traits to pass on: Organisms cannot choose which traits they pass on.

The antibiotic acts as a selection pressure. Bacteria with the resistance gene survive and reproduce, passing the gene on. Over many generations, a larger share of the population is resistant.

Wrong choices

• All bacteria of this kind die out.: The resistant bacteria survive and multiply, so the population does not die out.
• Each bacterium changes its own DNA on purpose to resist the drug.: Bacteria do not change on purpose. The resistant ones were already there and survived.
• The resistance gene disappears from the population.: The drug kills the bacteria without the gene, so the gene becomes more common, not less.

Moth color is inherited. On dark bark, dark moths were better hidden from birds, so they survived and reproduced more. Over generations, the dark form became more common. This is natural selection.

Wrong choices

• Birds preferred to eat dark moths.: If birds ate more dark moths, dark moths would have become rarer, not more common.
• Soot on the trees turned light moths dark.: Soot does not change a moth's genes. Moth color is an inherited trait.
• The moths chose to become dark to hide.: Organisms do not choose to change their inherited traits.

When people choose which animals or plants reproduce to get a desired trait, it is called artificial selection (selective breeding). Over many generations, the chosen trait becomes more common or stronger.

Wrong choices

• Extinction: Extinction means a species has died out completely.
• Homeostasis: Homeostasis is how a body keeps inside conditions steady.
• Natural selection: In natural selection, the environment decides which individuals reproduce. Here people chose.

Each branch point on a cladogram stands for a common ancestor. The more recent the branch point two groups share, the more closely they are related. Humans and chimpanzees share a more recent ancestor than humans and mice do.

Wrong choices

• Humans evolved from modern mice.: A cladogram does not show living species turning into each other.
• Humans evolved from modern chimpanzees.: A cladogram shows shared ancestors, not that one living species came from another living species.
• Mice are not related to humans at all.: Mice and humans are on the same cladogram, so they share an older common ancestor.

Human arms, whale flippers, and bat wings do different jobs, but they contain the same basic bones in the same order. Structures like this are called homologous structures, and they suggest the species share a common ancestor.

Wrong choices

• Many animals sleep more in winter.: Sleeping more in winter is a behavior, not evidence of shared ancestry.
• Plants grow toward a sunny window.: Growing toward light is a plant response, not evidence of common ancestry.
• Birds and insects both have wings.: Bird and insect wings are built very differently. They do the same job but do not come from a shared structure.

When a population is split by a barrier, the groups face different conditions and cannot interbreed. Over many generations, mutations and selection make them different. When they can no longer interbreed, they are separate species. This is speciation.

Wrong choices

• Artificial selection by people: No people chose which squirrels would breed.
• A mutualism between the two groups: Mutualism is two species helping each other. These groups are separated.
• An adaptation that one squirrel made during its lifetime: Speciation happens to populations over many generations, not to one animal during its life.