The New Pangloss

Life expectancy in the late paleolithic was 33 years; today it is 67. So we would expect (ceteris paribus) that "natural" things are unhealthy. Instead, the tag line "All-Natural" is almost always a claim that the "All-Natural" product is healthy.

This argument tends to misunderstand a basic evolutionary principle:

  • Evolution selects for gene propagation, not health

Everyone is probably familiar with extreme examples, like black widow spiders who practice sexual cannibalism. A canonical example of evolution's imperfection in humans is the appendix, whose function may be largely vestigial. The appendix shows the dangers of basing our actions on "evolution": even if we evolved an appendix so that our primate ancestors could better digest leaves, that doesn't necessarily imply that eating those leaves is the healthiest thing to do.

At the other end of the spectrum are the numerous fad diets based around the proposition that humans evolved to eat some certain amount or type of meat. But why should the evolutionary benefits of eating meat be related to health?

This was brought up by Jared Diamond in his book Why Is Sex Fun?, based largely on the paper "Why do Men Hunt?" by Hawkes, et al. They note that, as far as anyone can tell, hunter-gatherer societies would be better off (more and healthier kids) if they were just gatherer societies; that is, if men didn't hunt.1 So why do men hunt even though it hurts not just themselves but their children? Because if you bring down a big animal, you can trade that for extramarital sex, and it's better to have lots of extramarital kids, some of whom might starve to death, than to devote all your time to making sure a few intramarital kids live.

That's probably not something you'll find in the average diet book.

Voltaire parodied the idea that there is a compassionate god ensuring that natural events are good. Were Voltaire alive today, Candide might instead have poked fun at pseudo-Darwinians who claim that "Mother Nature" looks out for us.

  1. Note that "gathering" in this case can mean "hunting" small animals and fish, so it's not that the nutritional value of meat is greater. It might be better phrased as "Why do men hunt large animals instead of small ones?" There are several other possible objections that Diamond addresses in that book, which I won't repeat here.

Cost-Effective Ways to Fill Your Stomach

There is a large amount of fad dietary advice regarding which foods will fill you up. Holt et al. had an idea which was elegant in its simplicity: take a ton of people, and force them to eat some foods. A few hours later, place them in front of a buffet. The more people eat from the free buffet, the less full they must be.

There are some interesting confounds - for example, jelly beans seem to really fill people up. The researchers surmised that eating such large numbers of jelly beans made people too sick to keep eating.

Nonetheless, this gives us a nicely empirical measure of how full foods make you. We can then figure out what the cheapest food to eat is (assuming a full stomach is your goal).

FoodCost of 100 units of satiation (cents)Cost of 100 calories (cents)
Cod173400
Ground Beef2036
Baked Beans1831
Eggs1218
Lentils1013
Wheat Bread918
Potatoes (Red)826
White Pasta78
Whole Grain Pasta59
Rice46

Methodology

I used Peapod to find the prices of everything. In the event that there were multiple products in a category, I chose the cheapest. The original paper was not terribly specific (is "beef" ground beef? lean? steak?) but there was not a large difference between price per calorie of different types of food at the very cheap end, so this shouldn't matter too much. The only significant issue was that cod is vastly more expensive than anything else (probably due to overfishing); if any potential experimenters are out there, I would be interested in seeing the satiety index of cheaper fish like tuna. (Although if canned tuna were as satiating as cod, it would have a rating here of 44, which would still make it twice as expensive as beef!)

Using the price and nutritional information, I calculated the price per calorie. The satiety index tells us the satiety per calorie. Using (Price / Calorie) * (Calorie / Satiety) we can find Price / Satiety. This is the number presented here. Numbers are hundredths of cents per unit of satiety.

Raw data can be found here.

Conclusions

Unsurprisingly, vegetable-based foods are much cheaper. A less obvious conclusion is that broad groups of foods do not have the same cost effectiveness - for example, baked beans cost almost as much as beef, whereas lentils are half beef's cost.

A frugal meal of rice and lentils has three times the cost effectiveness of a meal of beef, and is an order of magnitude more effective than anything involving fish.

Do Non-human Animals Feel Pain?

A lot of speculation on non-human pain is through analogy. This table lists six things which seem to be important in human pain perception; by analogy, it seems that any being which also meets these criteria feels pain to some extent.

This table is an update of Varner's 1998 version. The most significant ambiguity in this table is in the insects, as there is some evidence that pain perception is different across insects with exoskeletons versus those with endoskeletons. I marked "some" insects as having nociceptors, as I was unable to find anyone who would make the categorical statement "All insects have nociceptors."

A "Y" means yes, blank means no, and question mark means the evidence is equivocal.

Invertebrates Vertebrates
Earthworms Insects Cephalopods Fish Amphibians / Reptiles Birds Mammals
Has Nociceptors? ? Some3-6 ? Y2 Y1 Y Y
Central Nervous System? Y Y Y Y Y
Nociceptors Connected to CNS? Y Y Y Y Y
Has Endogeneous Opiods? Y Y ? Y Y Y Y
Response Affected By Pain-killers? ? ? ? Y7,8 Y8,9 Y Y
Behavioral Pain Response? Y Y Y Y Y
Unless otherwise stated, all data comes from Varner, G. E. In nature's interests?: Interests, Animal Rights, and Environmental Ethics. Oxford University Press, USA, 2002. Other sources given by superscripts:
  1. Allen, C. “Animal pain.” Noûs 38.4 (2004): 617-643. Print.
  2. Sneddon, L. U., V. A. Braithwaite, and M. J. Gentle. 2003. Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system. Proceedings of the Royal Society of London. Series B. Biological sciences 270: 1115-1121. http://dx.doi.org/10.1098/rspb.2003.2349
  3. Pastor, J., B. Soria, and C. Belmonte. 1996. Properties of the nociceptive neurons of the leech segmental ganglion. Journal of Neurophysiology 75: 2268-2279. http://jn.physiology.org/cgi/content/abstract/75/6/2268
  4. Wittenburg, N., and R. Baumeister. 1999. Thermal avoidance in Caenorhabditis elegans: an approach to the study of nociception. Proceedings of the National Academy of Sciences of the United States of America 96: 10477-10482. http://www.pnas.org/cgi/content/abstract/96/18/10477
  5. Illich, P. A., and E. T. Walters. 1997. Mechanosensory neurons innervating Aplysia siphon encode noxious stimuli and display nociceptive sensitization. The Journal of Neuroscience 17: 459-469. http://www.jneurosci.org/cgi/content/abstract/17/1/459
  6. Tracey, J., W. Daniel, R. I. Wilson, G. Laurent, and S. Benzer. 2003. painless, a Drosophila gene essential for nociception. Cell 113: 261-273. http://dx.doi.org/10.1016/S0092-8674(03)00272-1
  7. Sneddon, L. U. “The evidence for pain in fish: the use of morphine as an analgesic.” Applied Animal Behaviour Science 83.2 (2003): 153-162. Print.
  8. Machin, K. L. “Fish, amphibian, and reptile analgesia..” The veterinary clinics of North America. Exotic animal practice 4.1 (2001): 19. Print.
  9. Machin, K. L. “Amphibian pain and analgesia.” Journal of Zoo and Wildlife Medicine 30.1 (1999): 2-10. Print.

Why these criteria?

Whatever the qualitative experience of pain comes from, it seems almost tautologically true that you first need to sense a stimuli in order to find it painful. So the requirement for nociceptors (or a direct analogue) is relatively straightforward.

The requirement of a centralized nervous system is probably equally straightforward at first glance: in order to be in pain, there needs to be a singular, distinct entity who is in pain. Varner notes that "Insects do not favor damaged limbs or become less active after internal injuries," implying that the "pain" insects feel, if any, is heavily localized.

If you have a mechanism to regulate pain, whether endogenous (i.e. created by the body) or through external drugs, that seems to indicate that the species has evolved not just to feel pain, but also to end pain that it feels. (Implying that not only is pain there, but it can also in some circumstances be "bad.")

Most theories for the evolution of pain assume that at least part of its function is to move away from noxious stimuli. Therefore, a lack of response seems to suggest a lack of pain sensing.

Conclusions

Evidence indicates that most of what we colloquially think of as "animals" feel pain. For at least cephalopods, Machin suggests that absence of evidence does not imply evidence of absence; there is stronger evidence that the lack of evidence for insects and worms is significant.