cages are also unatural , for that matter, the captive keeping /breeding of chameleons is unatural, even in a free range situation. are you suggesting that he should he should just let the temps fall where they may? what if one is expecting a low of 40* but the temps actually get down to 32* there are also other factors in determining the minimum tolerable temperature such as evaporative cooling , chill factor, humidity, health of the animal, length of time exposed , rewarmup condtions of the following day etc. if you take two seemingly similar animals (same genus, same sex, same age, same appearent health,recent stress, same conditions prior to having been kept outside, does not mean that they will both heve an exact same tolerance for minimum temp, one may do fine at 38* the other may perish at 40* just because generalizations have been made as to the minimum (or maximum) temperature any given animal is able to tolerate, that does not mean they should be tested. although i recognize that a reasonable unheated nightime drop is beneficial for many (even most) chameleons. any specific minimmum temperatures for any given genus can only be given as a general guidline. . if in doubt use a heat source. to me the safety of the animal takes precedence over creating natural conditions. if your goal is to be 100% natural regardless of the consequences , take it back to its native habitat and let it go