Perhaps the most enduring image of the concept of evolution is the "march of progress," the endlessly copied and parodied illustration of a straight-standing modern human heading up a line of predecessors that slowly regress to more apelike states. The idea of evolution as a teleological, or goal-oriented, process remains deeply ingrained in Western culture, and has served as the underlying basis for everything from the harmless sci-fi conceit of curiously humanoid aliens to the significantly less harmless products of the idea of "Social Darwinism." Were humans - and in particular the evolution of human-like intelligence - inevitable? While there is some dissent among scientists on this issue, the consensus appears to be no.
Stephen Jay Gould and "Glorious Accidents"
Probably the best-known popularizer of the role of contingency in evolution was the late paleontologist Stephen Jay Gould; in particular, his 1996 book Full House explained the concept of contingent evolution in terms non-scientists could understand. Gould, along with earlier evolutionist George Gaylord Simpson, felt that evidence pointed to humans and their particular intellectual gifts being lucky flukes that would likely not evolve again if the history of life on earth could be replayed.
To bolster his assertions, Gould drew attention to many chance occurrences in the planet's history that could have easily gone another way, subsequently sending evolution cascading down a very different path. Significantly for humans, he pointed to the interstellar impact 65 million years ago that annihilated a large number of species, most famously the dinosaurs. Had this cataclysm not occurred, he argued, the shrew-like mammals alive at the time would most likely not have speciated and evolved to fill the myriad niches left empty by the demise of the dinosaurs, and humans would probably never have emerged at all.
A Ladder of Progress With Humans at the Top
Many of those who advocate the view of humans as special or inevitable — the top rung on the "ladder" of evolution, so to speak - make much of the fact that other species that emerged before humans — whales and dolphins, elephants, some cephalopods, and of course other primates - have evolved intelligence, though none have approached the extraordinary cognitive sophistication of humans. They also believe that in evolutionary terms, intelligence is a highly adaptive trait; in general, it is better to be smart than dumb.
Human Intelligence an Unlikely Prospect
But for scientists and others supporting the chance-oriented model, the very rareness of intelligence stands against its inevitability. Yes, a few other species have evolved intelligence, but it is not nearly to the same degree as humans possess it, they argue, and besides, if human-like intelligence was inevitable, it should have appeared in many more species lineages and much sooner than a few million years ago, which is a mere eyeblink in the vast timescale of the evolution of life on earth. Philosopher Bertrand Russell summed up this view by stating, "If it is the purpose of the cosmos to evolve mind, we must regard it as rather incompetent in having produced so little in such a long time."
Further, while scientists agree that human-like intelligence is a unique and statistically improbable adaptation, given the timescale involved and the number of species that have emerged over that timescale, unique adaptations become ever more likely, however fantastic they may appear at first glance. Other species living today have unique, seemingly unlikely adaptations shared with no other known species - the bizarre tentacled olfactory organ of the star-nosed mole, to give just one example - but no one is arguing that these adaptations were a specific or inevitable "goal" of the evolutionary process.
Can Any Traits Be Said to be "Inevitable?"
In a 2008 article in Skeptic magazine, biologist David Zeigler listed a series of eleven adaptations that would likely evolve anywhere that conditions were conducive to life. He was speaking in the context of how extraterrestrial beings might be expected to emerge, but based his conclusions on the fact that these specific traits had emerged again and again in different species lineages on earth, suggesting that they were probably basic adaptations necessary for survival.
Among the traits he listed were the likelihood of being water-dependent and carbon-based; the possession of chemoreceptors in order to sense the surrounding environment; movement or locomotion; and genetic selfishness. He also felt that powered flight and water-based filter feeding were safe bets to emerge eventually. Further than that, though, he argued that evolution was not predictable, and that complex traits like intelligence were not inevitable outcomes of the process. In Zeigler's view, the argument that human-like intelligence was "meant to happen" is erroneous and based on an outdated teleological model of natural selection that partakes of a human-centric bias.
Sources:
Gould, Stephen Jay. Full House: The Spread of Excellence from Plato to Darwin. New York: Three Rivers Press, 1996.
Zeigler, David. "Predicting Evolution: How Likely is it that Human-level Intelligence Will Evolve Again?". Skeptic Vol 14 No 2 2008: 24-27.
Jenny Ashford - Jenny Ashford is a writer and graphic artist from central Florida. Her main area of interest in her Suite 101 articles is science, with a ...
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