The two gases that the blood carries around the body are and. .

Oxygen and carbon dioxide

Explanation:

Once the respiratory gases have diffused in the lungs, resulting in the blood becoming O2 rich and CO2 being exhaled, the next stage of transporting the O2 rich blood to the tissues that need it takes place.  

At the same time the next batch of CO2 rich blood must be brought to the lungs for the process to take place again.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".