Prof Andrew Loudon, from the University of Manchester, said: "The problems caused by living against the body clock may be less sexy than the countless 'this or that causes cancer stories' it is none-the-less a major problem for society".
By tracing the history of mutations that protect against the disease, researchers have shown that malaria probably became a major problem less than 12,000 years ago, and only reached southern Europe a few thousand years ago.
However, the provision of a light source for inspection of the cervix presents a major problem in less-developed countries, where candles and torches often provide the only means of illumination.
Americans are also concerned about voter suppression, but less so: 41 percent say it's a major problem, and 32 percent say it's a minor problem.
Crime, never a major problem, has become even less so in the last decade.
A major problem was limited coverage: less than half of the health staff participated in the training whereas a near 100%% coverage was the intention.
Measles is still a major problem in densely populated, less-developed countries with high birth rates and lacking effective vaccination campaigns.
And attrition, a major problem in the call center industry, is lower, less than 10percentt after the first 300 calls.
Charging time is a major problem in a car that can travel only 100 miles or less between charges.
This is a major problem in a country where, due to changing opinions and age replacement, socially conservative views are becoming less popular.
A major problem was parking.
