Narrator: This is Science Today. It's hard to imagine, but it's only been within this century that the average life expectancy for humans rose above what it was in Ancient Roman times. Roger McDonald, a professor of nutrition at the University of California, Davis, says life expectancy back then was about thirty years.
McDonald: Caesar was only about twenty when he started his campaigns. Alexander the Great was sixteen when he took over in Greece. So, you had to live very fast back then because you knew that your life expectancy was very short. And a lot of that was due to infectious diseases that would kill you off at young ages.
Narrator: McDonald says even until 1900, there was still no real appreciation of increasing life expectancy by getting rid of disease.
McDonald: We used to live around sewers, we used to not understand that simply washing your hands was going to improve health of the nation. And around 1920 we became very cognizant of that we needed to get people into hospitals to be born and about that time is when the life expectancy started to go up.
Narrator: For Science Today, I'm Larissa Branin.