 Consider the first group of criticisms.  If the human condition is not improving, either circumstances are getting worse, or they are fluctuating between some upper and lower bound.  Each alternative is certainly arguable.  Horrific human catastrophes, such as the genocides, wars, and environmental destruction of the 20th century, can bolster the argument that things are getting worse.  But less dramatic evidence, like increasing alienation in industrialized societies, could be cited in support of the same claim.  Then there are those who emphasize that natural limits will keep the human condition within certain bounds.  Either the natural environment or human nature could place limits on improvement and, for that matter, on deterioration. 