Chickpeas have become a familiar part of our diet as Mediterranean and Middle Eastern dishes have increased in popularity: hoummos is now a supermarket staple, and Elizabeth David and her successors have brought Spanish garbanzo stews and Italian ceci with pasta to the dinner tables of Middle England.

Although Cicer reticulatum formed part of the “founder package” of early crop domesticates in the Middle East about 11,000 years ago, along with wheats, barley, peas, lentils and bitter vetch, it was unique among them in not being widespread as a wild plant.

While the others are found more or less from Anatolia to Afghanistan, wild chickpeas are known only from a few locations in southeastern Turkey, although this is the region in which, if anywhere, the first farmers seem to have emerged.

Chickpeas also keep their seeds in the pod, not scattering them like wild peas and lentils, keeping stands of the plant small and localised. As a winter crop it is subject to devastating fungal attacks of Ascochyta blight, and in converting it to a summer crop to avoid this, farmers risk the loss of up to 90 per cent of the yield from water shortage.

In other words, chickpeas are not an easy or obvious domesticate, and their inclusion in the earliest crop package must have had some other reason.

Why “the rare and agronomically problematic chickpea” was chosen, including “the development of a novel agronomic practice, summer cropping, which may involve a considerable loss of the potential yield”, lay in its protein content, according to a study by Zohar Kerem and colleagues in the Journal of Archaeological Science. They suggest that experimental cultivation by early farmers yielded a seed with a high level of the important amino acid tryptophan.

“Dietary tryptophan determines brain serotonin synthesis, which in turn affects certain brain functions and human behaviour,” the investigators say, noting that its effects are perceived by both animal and human consumers. Extraction of the amino acid by microwaving and measurement by reversed-phase chromatography showed that chickpeas of both the larger Kabuli and the older and smaller Desi cultivated types had more than three times the tryptophan level of wild seeds.

The nutritional value of the cultivated seeds, measured using standard World Health Organisation criteria, was double that of wild seeds for children, and almost double for adults. “Our results suggest that consuming domesticated chickpea will elevate the levels of tryptophan available for processes other than growth and maintenance, for example bio-synthesis of brain serotonin,” the team says, noting that cooking did not affect the amino acid level.

Selection for a high-tryptophan crop such as chickpea “was dependent upon prehistoric humans’ ability to recognise naturally occurring variability”, meaning that the effects of eating even wild seeds must have been empirically appreciated. Farm animals have been seen to do just this and “diets enriched with tryptophan were recently shown to induce accelerated growth”, they say.

Tryptophan is a precusor of serotonin in the brain: more of the former in the diet leads to more of the latter in brain tissue, which in turn may create a well-fed feeling of satiety and at the same time increase ovulation rates in women. Serotonin is also implicated in cognitive ability, so “trytophan availability may affect cognitive performances related to social behaviour and emotional processing, especially under stress. This implicates tryptophan in lowering of aggression and decreased quarrelsomeness in healthy human volunteers,” the team reports.

Establishing this must have been a process of trial and error after initial observation of the wild seeds’ utility, and “the rarity of wild Cicer reticulatum and the agronomic difficulties involved in chickpea cropping call for an unorthodox explanation for the motivation to retain chickpea as a crop plant.” Cultivation raised the value of the plant enormously as a food source, and its association with higher ovulation rates, more frequent births and better-fed infants would have benefited early communities.

The cognitive benefits of serotonin would have led to more innovative cultural activities and increased self-confidence, the authors surmise. “The choice of chickpea should be looked upon as another step in establishing a new human-environment relationship, in which accumulation of knowledge through complex trial-and-error processes ended up in the adoption of this staple plant.”

This research suggests that hoummos, with olive oil and sesame paste, as well as chickpeas, seems to be a dish good for the body, the mind, and one’s sense of wellbeing.

Journal of Archaeological Science 34: 1289-93