From Visions: How Sci­ence Will Rev­o­lu­tion­ize The 21^st Cen­tury by Michio Kaku:

Gen­er­a­tions of high school chil­dren gasp when they read Shakespeare’s Romeo and Juliet, for they are amazed to dis­cover that Juliet was only thir­teen years old. We some­times for­get that, for most of human exis­tence, our lives were short, mis­er­able, and brutish. Sadly, for most of human his­tory, we repeated the same wretched cycle: as soon as we reached puberty, we were expected to toil or hunt with our elders, find a mate and pro­duce chil­dren. We would then have a large num­ber of them, with most of them dying at child­birth. As Leonard Hayflick says, “It is aston­ish­ing to real­ize that the human species sur­vived hun­dreds of thou­sands of years, more than 99% of its time on this planet, with a life expectancy of only 18 years.” Since the indus­trial rev­o­lu­tion, thanks to increased san­i­ta­tion, sewage sys­tems, bet­ter food sup­plies, labor-​​saving machines, the germ the­ory, and mod­ern med­i­cine, our life expectancy has risen dra­mat­i­cally. At the turn of the cen­tury, the aver­age life expectancy in the United States was 49. Now, it is around 76, a 55% increase in a cen­tury. As Joshua Leder­berg notes, “In the U.S., greater life expectancy…can be attrib­uted almost entirely to this mas­tery of infec­tion, this anni­hi­la­tion of the bugs.” And today, the fastest-​​growing seg­ment of our pop­u­la­tion is the group that is over a hun­dred years old.”