An observer may be reminded of Darwin's theory of natural selection, according to which living creatures adapt to fit a wide range of environmental niches. Extending the Darwinian analogy, the standard reconnaissance unmanned aerial vehicle (UAV) of the past was a medium-sized pterodactyl equipped with a film camera. Today's vehicles range in size from hummingbirds such as the experimental 50g Aero Vironment Black Widow to the 11,000+kg Northrop Grumman RQ-4A Global Hawk, a battle-tested condor of the UAV world. Pressure to evolve comes, as ever, from the demands of war. Recent conflicts in the former Yugoslavia, Afghanistan and Iraq have shown the value of an eye in the sky which can tell the soldier what lies over the hill, map terrain, guide missiles to their targets, sniff out chemical weapons or find hostile radar. UAVs offer smaller, more agile, less visible platforms for surveillance equipment and weapons, do not risk a human pilot and are cheaper, and hence more expendable, than missiles or manned vehicles.
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