Short-term environmental changes—like the season of heavy snow and rainfall that led to an outbreak of hantavirus in 1993—are dangerous, if minor, threats. Long-term changes pose a much greater risk, because they permanently alter the interactions of species living in an affected area. Changes to our prehistoric landscape, and living patterns brought by human agriculture, have made diseases like malaria a major threat in tropical regions.

While malaria is no mystery-scientists have long identified the microbe that causes it—various factors have prevented us from eradicating the disease. Environmental changes, evolutionary changes in microbes and mosquitos, and human behavior have all contributed to the longevity of this microbe, and limit our chances for defeating it.

Malaria now infects some 300 million people each year, killing at least 2 million children and adults. Two children die of malaria every minute.