Using the fossil record, you can categorize species based on analogous or homologous structures
The Dependant Variable is the one responding to change.
Control Variables are controlled by you, and you influence the Independent Variables.
What do you mean by following?
Predators and prey are both in a constant struggle for survival, foxes with bigger ears tend to catch more mice, and live longer, because of this, foxes with smaller ears don't live as long, pretty soon all foxes have larger ears. The same goes for prey, Mice with padded feet live longer due to the foxes having more trouble hearing them, pretty soon all mice have padded feet, and the cycle continues.
The answer would be Haemoglobin.
The Haemoglobin is a red pigment found in RBCs of vertebrates that helps to transport oxygen to various tissues.
Vertebrate blood is bright red when it is oxygenated and dark red when it is deoxygenated. Some animals such as crustaceans or mollusks, use haemoglobin to carry oxygen instead of hemoglobin.
Hope This Helped!
