Food Handling

Plants make up the bulk of the diet of most primate species. Plants must use morphological, mechanical, or chemical defenses to protect themselves. 

Chemical defenses include the presence of secondary compounds. Secondary compounds can act as anti-feedants as "digestive inhibitors" or as "toxins". Digestion inhibitors include: tannins, proteinase inhibitors, anti-microbial compounds or lignin. Major classes of toxins include alkaloids, phenolics, tannins, saponins, cyanogenic glycosides, rotenoids and other flavonoids, sesquiterpenes, diterpenes, pyrethrins, and non-protein amino acids and cyanide glycosides (Chapman and Chapman 2002; Rosenthal and Janzen 1979). These secondary compounds can be found in leaves, seeds, pith, husks, flowers, gums, and barks.

Several primate taxa, such as colobine monkeys, have evolved dental and gastrointestinal features that allow them to overcome diets high in secondary compounds (Lambert 1999). Great apes, including humans, do not possess a specialized gut to process foods that are high in secondary compounds and must avoid these compounds in alternative ways.

HUMANS:

Humans consume foods with high levels of plant derived secondary compounds that include ascyanide, quinine, morphine, cocaine, caffeine, and nicotine (Glander 1982; Siegler 1977). The plant family Solanaceae contains several foods routinely consumed by a wide variety of human populations that includes foods such as potatoes, tomatoes, eggplant, and pepper (Chaube and Swinyard 1976).

Mechanical processing of secondary plant compounds may include the removal of indigestible or toxic plant parts or cooking, which acts to destroy tannins. For example, among the Hadza hunter-gatherers of Tanzania, several methods of food handling are used. Seed husks of the baobab fruit are winnowed away prior to ingestion and the fibrous quid of certain species of tubers are expelled before consumption.

CHIMPANZEES:

Chimpanzees have been reported to avoid alkaloid rich fruits (Hladik 1977) and exhibit a preference for ripe fleshy fruits that contain large quantities of tannins when unripe. Chimps process unripe fruit by removing the seeds from the pulp before consumption and discarding any pulp that is tannin rich (Waterman 1984). "Wadging" (Goodall 1986) is an alternative mechanism of seed extraction in which fruit is pressed against the anterior dentition while the fruit juice is sucked out, making a wadge of pulp, skin, fiber, and seeds; the seeds are discarded once the juice has been consumed (Lambert 1999).

GORILLAS:

Mountain gorillas select leaves that are low in tannins (Watts 1984). They possess an enlarged hindgut relative to chimpanzees and have higher rates of fermentation via cellulose digesting microflora (Bauchop 1978; Chivers and Hladik 1980). Gorillas may also practice geophagia to facilitate consumption of secondary plant compounds (Remis 1997). Gorillas also consume foods that contain spiny plant parts and nettles and employ mechanical removal by folding nettles inside the plant before consumption (Byrne 2001).

The presence of various food handling behaviors among extant great apes suggests that secondary plant compound processing or avoidance behaviors were present in early hominins.