--The title of this post should be, "Are intelligent beings necessary?" or some such; see Ruse's title.
-- Via Three-toed sloth , a whole conference on complexity and evolution, and a book (reviewed by Cosma) about how the complexity of life on Earth might have been stabilized ("fixed") during natural selection. Clearly there's more going on here than I first appreciated, though I remain close to Gould.
Here's the original post:
Michael Ruse has a wonderfully written essay at Philosophy of Biology about the idea that humans are the pinnacle of evolution. A suprising (to me) number of thinkers, believe that a very common result of natural selection is an increase in complexity; and that, by extension, that Homo Sapiens or in any case a social, intelligent, environment-altering lifeform, is essentially inevitable. Here is E.O. Wilson as quoted by Ruse:
“the overall average across the history of life has moved from the simple and few to the more complex and numerous. During the past billion years, animals as a whole evolved upward in body size, feeding and defensive techniques, brain and behavioral complexity, social organization, and precision of environmental control – in each case farther from the nonliving state than their simpler antecedents did.”
A slightly less emphatic statement of the same idea comes from Conway Morris's notion of a sort of quantization of niches. For example, marsupials and placental mammals both gave rise to very similar-looking predators. Somehow intelligence and culture have beckoned in our era, the Cenozoic; thus Humans. (If not humans, then a cultural animal arising from a different lineage. Ninja turtles, anyone?)
Ruse himself does not come down with an opinion, so let me supply one: the law of natural selection by itself does not specify what will improve survival. (Ruse metntions this point, citing Stephen Gould, in his essay, then strangely abandons it at at the end). Thus, at the most basic level- given life on a World X would it *necessarily* become complex over time, I have to answer, emphatically, no, not necessarily. Whether the range of niches supplied by Cenozoic-era Earth led to an evolutionary gradient which our primate ancestors filled (with us) is speculative to the point of being a bit weird. Even the softer version of Wilson that simple "tends to" give rise to complex with time just does not feel written in stone to me.