1. From 1984 to 2012, the wing length of cliff swallows in the general population generally decreased.
2. During the same time period, the wing length of cliff swallows killed on the roads generally increased.
3. In most years where data was collected, the wings of cliff swallows killed on the roads were longer than the wings of swallows found in the population at large.
4. Shorter wings allow cliff swallows to take off from the ground more vertically, enabling them to better avoid oncoming cars. As a result, cliff swallows in populations near highways with shorter wings have a survival advantage.
5. The data suggest that, over time, natural selection resulted in the evolution of shorter wings in the cliff swallow population.
6. Shorter wings are a(n) adaptation in this population. Alleles for shorter wings were already present in the general population.

stratosphere: as the altitude increases, the air temperature increases. the stratosphere has a layer of ozone, called the ozone layer. this layer absorbs most of the ultraviolet radiation from sunlight. this results in the stratosphere being warmer.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.

where is the scientific experiment?