Why did separate systemic and pulmonary circulations evolve in species that have the high-pressure circulatory system required for rapid movement of blood?

The separate systemic and the pulmonary conditions all evolve in the species that are having the high pressure circulatory system required for rapid movement of blood because if pulmonary was under pressure as high as that of the system circulation.

Explanation:

Here, it is given that the separate systemic and the pulmonary circulations evolve in the species.

And those species have the high pressure circulatory system for blood movement rapidly because if the pulmonary was under pressure as high as that of systemic circulation.

Also the fluid amount that will flow would be forced out of the cappilaries in the lungs.

Now, there is a conflict between the thin surface required for efficient exchange of gases.

Also, the thick blood vessels are required to withstand the high blood pressures.