SCIENCE VALUES DATA and statistics and champions the virtues of evidence and experimentation. Those of us “viewing the world with a rational eye” (as the new descriptor for this column in Scientific American reads) also have another, underutilized tool at our disposal: rapier logic like that of Christopher Hitchens, a practiced logician trained in rhetoric. Hitchens—who is “leaving the party a bit earlier than I’d like” because of esophageal cancer, as he lamented to Charlie Rose in a recent PBS interview—has something deeply important to offer on how to think about unscientific claims. Although he has no formal training in science, I would pit Hitchens against any of the purveyors of pseudoscientific clap trap because of his unique and enviable skill at peeling back the layers of an argument and cutting to its core.

We would all do well to observe and emulate his power to detect and dissect baloney through pure thought. To wit, after watching a quack medicine man fleecing India’s poor one Sunday afternoon, the belletrist scowled in a 2003 Slate column, “What can be asserted without evidence can also be dismissed without evidence.” The observation is worthy of elevation to a dictum.

Of course, as scientists we prefer to tether evidence, when it is available, to logical analysis in support of a claim or to proffer counterevidence that disputes a claim. A radiant example of Hitchens’s insightful thinking, coupled to the effective employment of counterevidence, is his reaction to an episode of the television series Planet Earth. As he watched, he had a revelation of creationism’s profound flaws. The episode was on life underground, during which Hitchens noticed that the blind salamander had “eyes” that “were denoted only by little concavities or indentations,” as he recounted in a 2008 Slate commentary. “Even as I was grasping the implications of this, the fine voice of Sir David Attenborough was telling me how many millions of years it had taken for these denizens of the underworld to lose the eyes they had once possessed.”

Creationists make a big deal about the eye, insisting that the gradual stepwise process of natural selection could not have sculpted such a complex instrument because of “irreducible complexity,” meaning that the removal of any part would render it useless. Even Charles Darwin fretted about the eye in On the Origin of Species: “To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.”

If God created the eye, then how do creationists explain the blind salamander? “The most they can do is to intone that ‘the Lord giveth and the Lord taketh away,’” Hitchens mused. “Whereas the likelihood that the postocular blindness of underground salamanders is another aspect of evolution by natural selection seems, when you think about it at all, so overwhelmingly probable as to constitute a near certainty.” To confirm his instincts, Hitchens queried evolutionary biologist Richard Dawkins, who agreed: “Why on earth would God create a salamander with vestiges of eyes? If he wanted to create blind salamanders, why not just create blind salamanders? Why give them dummy eyes that don’t work and that look as though they were inherited from sighted ancestors?”

Hitchens’s point is even deeper, however, when he applies the counterfactual argument of regression to the cosmos itself, noting that “there is a dialectical usefulness to considering the conventional arguments in reverse, as it were. For example, to the old theistic question, ‘Why is there something rather than nothing?’ we can now counterpose the findings of Professor Lawrence Krauss and others, about the foreseeable heat death of the universe…. So, the question can and must be rephrased: ‘Why will our brief ‘something’ so soon be replaced with nothing?’ It’s only once we shake our own innate belief in linear progression and consider the many recessions we have undergone and will undergo that we can grasp the gross stupidity of those who repose their faith in divine providence and godly design.”

The dialectical usefulness of clear logic, coupled to elegant prose (layered on top of the usual dollop of data), cannot be overstated and should be considered by scientists as another instrument of persuasion in the battle for ideas.

What are the odds that intelligent, technically advanced aliens would look anything like the ones in films, with an emaciated torso and limbs, spindly fingers and a bulbous, bald head with large, almond-shaped eyes? What are the odds that they would even be humanoid? In this YouTube video, produced by Josh Timonen of the Richard Dawkins Foundation for Reason and Science, I argue that the chances are close to zero. Richard Dawkins himself made this interesting observation in a private communication after viewing it:

I would agree with [Shermer] in betting against aliens being bipedal primates, and I think the point is worth making, but I think he greatly overestimates the odds against. [University of Cambridge paleontologist] Simon Conway Morris, whose authority is not to be dismissed, thinks it positively likely that aliens would be, in effect, bipedal primates. [Harvard University biologist] Ed Wilson gave at least some time to the speculation that, if it had not been for the end-Cretaceous catastrophe, dinosaurs might have produced something like the attached [referring to paleontologist Dale A. Russell’s illustrated evolutionary projection of how a bipedal dinosaur might have evolved into a reptilian humanoid].

I replied to Dawkins that if something like a smart, technological, bipedal humanoid has a certain level of inevitability because of how evolution unfolds, then it would have happened more than once here. In his 2001 book Nonzero: The Logic of Human Destiny, Robert Wright argues that our existence precludes other terrestrial intelligences of our level from arising. But Neandertals were as close as one can get to a counterfactual experiment: they had hundreds of thousands of years to themselves in Europe without our interference and showed nothing like the technological and cultural progress of the modern humans who displaced them. Dawkins’s rejoinder to me is enlightening:

But you are leaping from one extreme to the other. In the film vignette, you implied a quite staggering rarity, so rare that you don’t expect two humanoid life-forms in the entire universe. Now you are … pointing out, correctly, that a certain inevitability would predict that humanoids should have evolved more than once on Earth! So, yes, we can say that humanoids are fairly improbable, but not necessarily all that improbable! Anything approaching “a certain inevitability” would mean millions or even billions of humanoid life-forms in the universe, simply because the number of available planets is so huge. Now, my guess is intermediate between your two extremes … I suspect that humanoids are not so very rare as to justify the statistical superlatives that you permitted yourself in the vignette.

Good point. But of the 60 to 80 phyla of animals, only one, the chordates, led to intelligence, and only the vertebrates actually developed it. Of all the vertebrates, only mammals evolved brains big enough for higher intelligence. And of the 24 orders of mammals only one — ours, the primates — has technological intelligence. As the late Harvard evolutionary biologist Ernst Mayr concluded: “Nothing demonstrates the improbability of the origin of high intelligence better than the millions of phyletic lineages that failed to achieve it.” In fact, Mayr calculated that even though there have evolved perhaps as many as 50 billion species on Earth, “only one of these achieved the kind of intelligence needed to establish a civilization.”

The late astronomer Carl Sagan, in a Planetary Society debate with Mayr (Bioastronomy News, Vol. 7, No. 4, 1995), noted that technologically communicating species “may live on the land or in the sea or air. They may have unimaginable chemistries, shapes, sizes, colors, appendages and opinions. We are not requiring that they follow the particular route that led to the evolution of humans. There may be many different evolutionary pathways, each unlikely, but the sum of the number of pathways to intelligence may nevertheless be quite substantial.”

Thus, the probability of intelligent life evolving elsewhere in the cosmos may be very high even while the odds of it being humanoid may be very low. I strongly suspect that we are blinded by Protagoras’ bias (“Man is the measure of all things”) when we project ourselves into the alien Other.