Name the three variables that you had to keep constant or controlled​

The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

The asian shore crab (hemigrapsus sanguineus) is an invasive species that has impacted the atlantic coast. predict what characteristic of this invader would most likely disrupt the biodiversity of this area.

Which of the following typically characterizes a tropical rainforests