The science of cannibalism

hink you're discriminated against? Pity the poor cannibals. We make jokes to hide from the horror of it, but in some parts of the world cannibalism from starvation is still within living memory.

After Biden claimed that his relative had been eaten in New Guinea, residents of the island, now a rising exporter of nickel with a 2.8% unemployment rate, were deeply offended, saying “they wouldn't just eat any white men that fell from the sky.”

A White House spokesman dictated that we must not make jokes about it. Telling us what we can and cannot say, of course, is waving red meat in front of the Internet. Maybe we laugh about Biden for much the same reason as we laugh about cannibalism: because neither is funny.

I leave it to the shrinks to help us understand why cannibal jokes are funny. But the bitter truth is that many animal species, including dogs ^[1], fish, and locusts ^[2], partake of canni­bal­ism. Anyone who raises tropical fish or breeds mice knows the difficulty in keeping them from eating one another. Chickens don't just henpeck each other; they are sometimes beak-trimmed to prevent them having each other over for chicken dinner. ^[3]

Cannibalism as a strategy of plants and insects

Cannibalism (no connection with cannabinoids), is the consumption of conspecifics. It is such a prevalent survival strategy that locusts have evolved a specific pheromone, identified as phenylacetonitrile, released under crowded conditions, that inhibits them from eating each other.^[2]

While spiders are well known to practice cannibalism, it turns out that male spiders have evolved a catapult mechanism to avoid being eaten. ^[9]

Bordered patch butterflies [Chlosyne lacinia] engage in cannibalism to acquire sodium. Plants don't need sodium, so herbivores such as butterflies must acquire it from their conspecifics when sodium is too low. ^[4] Plants are no saints either, and tomato plants [Solanum lycopersicum] have evolved a diabolical strategy that induces herbivores to commit cannibalism as a strategy of reducing herbivore abundance.^[5] Tomatoes also induce cannibalism among Helicoverpa zea (corn earworm) moths.^[6]

How this works at the molecular level, and what effect (if any) eating too many tomatoes may have on humans, remain to be investigated. Idaho is the only state in the US with a specific law against cannibalism. Yet Idaho is not even in the top ten in tomato production. That honor belongs to California.

While no plant has so far passed a Turing test, there is still doubt among some scientists as to whether plants are intelligent. Citing a study that claimed to demonstrate conditioned learning in green pea plants [Pisum sativum L.], the authors of one article ^[7] claimed that 68% of respondents to their questionnaire believed that plants are intelligent. Just so you know where this is going, a clue is in the post-structuralist drivel in the section titled “Different forms of knowing and knowledge”:

[F]rom a non-Western cultural perspective, the ontology and epistemology of understanding natural phenomena is perceived differently, which in turn contributes to the constitution of a worldview. For example, the ontology that plants (and nature) are agents (or 'persons' and not 'objects') is commonly shared in some traditional cultures and has been elaborately described in the anthropological literature [40–42]. Traditional knowledge (TK) (also known as traditional ecological knowledge or TEK) is more holistic, subjective, and qualitative than Western scientific knowledge [43].

They also cite a study claiming that Venus flytraps [Dionaea muscipula] plants are able to count to five. Eleven percent of those agreeing that plants are intelligent agreed with the statement “A plant or tree has spoken to me before.”

I hope I don't have to tell you this belief is not widely shared among scientists.

Silence of the cannibals

It's well known that certain Native American tribes sampled each other in times of famine and as part of rituals ^[8] perhaps associated culturally with the Wendigo cult. As in any article discussing these ethnic groups, the anthropologists walk on eggshells:

Engaging in discussions about cannibalism necessitates cultural sensitivity and respect for diverse cultural practices and beliefs to foster open dialogue and enhance cross-cultural understanding. . . .

To navigate this complex subject with sensitivity and respect, it is essential to recognize the diverse manifestations and motivations behind cannibalistic behavior, whether in the context of Wendigo psychosis or other cultural practices.

The authors say that cannibalism is “deeply engrained in the cultural and mythological heritage of Algonquian-speaking tribes.” According to the authors, the mythical rapacious Wendigo spirit, which resembles a cross between werewolf and zombie, represents “the dread of limited resources during harsh winters and the dangers of yielding to personal greed.” Once a victim of Wendigo psychosis eats human flesh, they are supposedly changed permanently into a Wendigo.

Among modern humans, aside from starvation conditions, cannibalism falls into two groups: persons with schizophrenia use it as a self-defense reaction, while in mixed personality disorder it is thought to be a desire to overcome deep-rooted frustrations. ^[10] Cannibalism is usually associated with psychosis, intellectual disability, or substance abuse. Between 4 and 23% of patients with genetic disorders such as Angelman syndrome and Lesch-Nyhan syndrome, which produce intellectual disability, exhibit self-injurious behavior but rarely engage in cannibalism.

Nutritional value of human diets

Scientists have questioned earlier studies claiming that tribes that abandoned cannibalism experienced a decline in general health.^[11] Others suggested that cannibalism-spread diseases like kuru and CJD could be protective adaptations to cannibalism, since they can only be spread by ingesting brains of deceased individuals.

According to an authoritative 2017 report by James Cole in Scientific Reports^[12] that gets to the meat of the matter, the human brain is a mere snack at only 2706 calories, which is only 1.88% of the caloric content of the entire human body, which contains 143,771 calories. Of this, 34% comes from fat. By com­par­i­son, a mammoth was estimated to contain 111 times more calories—3,600,000 calories from skeletal muscle alone, compared to only 32,376 for the human. Even an ordinary deer, say the researchers, is 3.67 times as nutritious as skeletal muscle from a human, containing 119,040 calories. The authors won an Ig Nobel prize for this work.

Researchers at Oxford found that nutrient-imbalanced wolf spiders (Pardosa prativaga [Koch]) utilized an alternative diet less efficiently than spiders on a balanced diet. They found that diet makes a population dimorphic, with spiders fed an unbalanced diet unexpectedly showing greater reluctance to engage in cannibalism.^[11]

There you have it. Maybe that's why we eat junk food: we subconsciously recognize that it reduces our cravings for each other. Or maybe humans, like locusts, emit an anti-cannibal pheromone. Considering how badly researchers mishandled the studies on human sexual pheromones, it would not be surprising to find that pheromones influence much of human behavior. Given the dog-eat-dog nature of academia, can we really rule out a deficiency of anti-cannibal pheromone at our universities? Good project for some hungry postdoc to get his or her teeth into.

apr 23 2024, 5:54 am. updated apr 24 2024, 3:12 pm