It was a scant few decades ago that Venus was commonly thought to be a companion planet to the earth, probably capable of supporting life in a rainy, carboniferous, swampy environment. While numerous speculations of the possible existence of various life forms were rife, the obscuration of the planet's surface by its cloud layers prevented more “detailed” interpretations of Venus such as those Lowell and others were able to make for Mars, where surface markings were easily distinguishable by telescope.
Venus is now known to have as diverse a set of characteristics and to be as unique in its own right as any of the nine known planets in the solar system. Although scientists search for underlying principles by which to describe and ultimately to understand nature, it is abundantly clear now that each of the solar system planets, including Venus, has a significant number of unique characteristics which distinguish one from the other. Some of these characteristics may be only incidental to planetary evolution, but we are not absolutely confident as yet which are central to fundamental understanding and which can be ignored (is the unique existence of life on earth central or only incidental to this planet's evolution?).