Regarding the Nov. 5 front-page article “Other potential Earths? Try 25 billion of them”:

The number of “Earth-like” planets tells us nothing about the probability of life elsewhere in the universe. Despite the Earth being apparently perfect for life, this is, of course, backward thinking: Life is the way it is because of the way conditions on Earth existed at the time of its origin and how life and the Earth evolved since then.

More important, it is likely that all life on Earth evolved from a single ancestor, as evidenced by its identical composition (DNA, RNA, etc.) and structure. You cannot argue probability from a single event, no matter how large the number.

F.J.R. Taylor, Deep Cove, North Vancouver, B.C.