Why Are Humans Always So Sick?

The swine flu outbreak this spring is just the latest in the mountain of ailments that seem to beset humanity, from the incurable common cold to each potentially deadly cancer diagnosed at the rate of every 30 seconds in the United States.
So is our species sicker than it has ever been? Or is our current lot far better than it used to be?
It turns out the answer to both questions might be yes. While humans as a whole do live longer than ever before, we now suffer certain illnesses to a degree never seen in the past — including skyrocketing rates of diabetes and obesity and, surprisingly, ailments such as hay fever.
Among the possible causes for our modern ills: super-hygiene, sedentary lifestyles, and a lack of worms in our stomachs.

Life expectancy shot up dramatically on average across the world during the 20th century, increasing from just age 30 or so in 1900 to roughly age 67 now. (It’s not that many people didn’t live to ripe old ages back then. Rather, the shift was due in large part to vast reductions in the number of infant deaths, which brought the average way down.) In 1900, there was just one country worldwide where under one in ten children died before their first birthday, while now out of the 187 nations for which there is data, this holds true for 168. These striking changes are due in large part to improvements in nutrition, sanitation and medicine.
"As a world population, on average we are far healthier than before," said historian of medicine Naomi Rogers at Yale University.