In 1850 there was a large snowshoe rabbit population in manitoba, canada. over the years, the winter coloration (the color of the rabbit's fur) of the surviving rabbit population changed. the graph shows the change in winter coloration of rabbits between 1850 to 2000. based on the data, we could hypothesize that

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.