Ms. Angier proceeded to describe some of the surprising ways that plants help to ensure their own survival. As someone who loves learning about the natural world, I am endlessly fascinated with the clever self-preservative tricks that Earth's organisms have devised. In plants, these range from resource foraging (e.g., growth oriented toward brightly-lit and nutritive soils) to chemical warfare (e.g., releasing irritants to ward off nibbling predatory insects). Plants are certainly far more complex and worthy of examination than many people think -- and than most biology curricula demand, my own undergraduate studies included. It's always nice to see plants get their brief moments in the sun.

But from these descriptions of how plants deal with the sometimes nasty vicissitudes of their lives, Ms. Angier extrapolates a fairly ridiculous conclusion: that vegetarians cannot (on the basis of their diets) claim to be living any more ethically than their carnivorous neighbours. Why? Because plants, like animals, "fight to survive".

Well, of course they do. Survival and reproduction are the two core biological imperatives, the literal sine quibus non (‘without which, nothing') of all species. Life, to the extent that it can truly be said to be purposeful, has an overarching ‘goal' of ensuring more life. Evolutionary mechanisms thus ensure that survival and defense mechanisms are emergent properties of species. In that sense all living things, including plants, should ‘like' or ‘want' to live and reproduce. (Using mental metaphors to describe non-humans is fraught with intellectual peril, which is why I put these and similar terms in scare quotes.)

But by that definitional logic, so too do Ebola viruses, cancers, and liver flukes ‘like' to live and reproduce. Indeed, they're all quite frighteningly good at it -- weakening and ultimately killing their hosts as they successfully multiply. So, Ms. Angier, shall we be truly ethical, let life take an absolutely natural course, and shut down our hospitals? This is a clearly silly conclusion.

To live, we humans must consume some form of nutritive biomass; rocks and sunlight just won't cut it. We can agree that all plants and animals have the ‘goal' of survival. We can agree that by eating them, humans generally frustrate that goal -- fictional creatures like Schmoos (http://en.wikipedia.org/wiki/Shmoo) and Ameglian Major Cows (http://www.youtube.com/watch?v=C1nxaQhsaaw) notwithstanding. And we can agree that we do not yet have the needed technology to circumvent this problem. (The food replicators of Star Trek could do the trick nicely; alas, they remain the stuff of fiction.)

So shall we vegetarians fall upon our forks? Are we doomed to learn the mystical secrets of breatharians (http://en.wikipedia.org/wiki/Inedia) or else waste away, starving but self-satisfied?

Plants, it is true, are laden with features -- like thorns, trichomes, and toxins -- that reduce the chances they will be targeted by herbivores or parasites. Such features likely evolved primarily for protective value rather than, say, for sturdiness or as accidental metabolic byproducts. Recent evidence even suggests that some plant species can recognize genetic kin in their surroundings and may even behave ‘altruistically'. For example, plants might show slower growth in the presence of close relatives, implying a possible sharing of available soil and water resources (http://www.wired.com/wiredscience/2009/11/plant-family-values/).

So can plants detect tissue damage and respond to environmental threats? Almost certainly. Can they feel fear and pain in a way that we can comprehend? Almost certainly not. The best evidence we have at present concerning plant anatomy and physiology would imply that they could not -- even in principle -- have psychological experiences comparable to animal species. Plants have no discernable brains or other nervous tissues. Stimulus response cannot be equated to "feelings" or "consciousness".

But if plants can feel pain, it actually makes the argument against meat-eating even stronger. Why? Simple: if you trace down the food chain for almost any animal species, the base of the food pyramid is going to be composed of plant material. Up to 90% of biomass energy gets lost each time we move up a link in the chain. If grass feels pain, and you eat two pounds of beef (which required, let's say, 15 agonized pounds of digested grass to produce), then you've indirectly caused needless extra suffering.

Ms. Angier also ignores the fact that some plants actually count on being consumed -- in whole or in part -- for their unique life cycle mechanisms to occur. For example, many plants grow berries and seeds with the ‘intent' that these be eaten and later deposited at some new growing location. (And in a fresh pile of fertilizer, no less!) I am hard-pressed to think of any non-parasitic animal that does the same.

In summation, to Ms. Angier and her ideological supporters, if you think that you'll ever see the same kind of terror in the eyes of an uprooted Idaho potato as you will in those of a slaughtered Jersey cow, I would respectfully suggest that you're kidding yourself. If you want to eat meat, do it. But don't try to argue for moral equivalence with absurd tu quoque arguments.

And to my colleagues and constant readers here at PT... Thank you for your engaging comments over the past months. Whether or not you've agreed with what I've written, I hope that my little corner of the blogosphere has merited an occasional glance and prompted some critical thought. I have sincerely appreciated the positive feedback and tried to learn from the constructive criticism. I look forward to conveying cutting-edge cognitive comestibles to chew on come 2010.

Have a safe and happy holiday season!!

Extra Credit Section

If I listen closely, I can almost hear the wheels of cognitive dissonance spinning out there. Many readers who were previously salivating in anticipation of this weekend's impending ham or turkey feast are now simply frothing. So, let me preemptively address some of the most probable responses:

"Eating meat is pleasurable -- more than its alternatives, certainly. Therefore, I choose to do it."

This is a childish argument from hedonic consequence. My wife -- a happy meat eater -- thinks that childish is too strong a word, but I disagree. Replace "Eating meat" with "Unprotected sex" (or, perhaps, "Punching preachy vegetarians in the face") and you can quickly see why.

Most schools of hedonic ethics require that you consider the costs of your actions, not just the benefits.  Indeed, Epicurus, a major philosophical father of this line of ethical thought, clearly insisted in his Letter to Menoeceus that the good life is obtained through careful reflection about behavioural choices, not "the enjoyment of the fish and other delicacies of a luxurious table".