For thousands of years, human beings have struggled to beat the heat. While ancient cavemen and early civilizations turned to natural methods to stay cool, modern humans utilize technology and electricity to keep cool. From the first steam-powered refrigeration machine to changeable air filters today, humans have created simpler and simpler ways to keep the heat out through the warm months. You may be surprised to learn that our ancestors put keeping cool at the top of their to-do list, too! However, personal comfort wasnâ€™t always their motive. Keeping body and food temperature down was essential to survival. Check out this timeline to see how the HVAC systems we now take for granted came to be out of pure human innovation!