Journal of Archaeological Science 34 (2007) 1289e1293
http://www.elsevier.com/locate/jas
Chickpea domestication in the Neolithic Levant through the
nutritional perspective
Zohar Kerem a,*, Simcha Lev-Yadun b, Avi Gopher c, Pnina Weinberg a,
Shahal Abbo d
a
Institute of Biochemistry, Food Science and Nutrition, The Faculty of Agricultural, Food and Environmental Quality Sciences,
The Hebrew University of Jerusalem, P.O. Box 12, Hertzle Street, Rehovot 76100, Israel
b
Department of Biology, Faculty of Science and Science Education, University of Haifa e Oranim, Tivon 36006, Israel
c
Institute of Archaeology, Tel Aviv University, Ramat Aviv 69978, Israel
d
R.H. Smith Institute of Plant Science and Genetics in Agriculture, The Faculty of Agricultural, Food and Environmental Quality Sciences,
The Hebrew University of Jerusalem, P.O. Box 12, Hertzle Street, Rehovot 76100, Israel
Received 14 June 2006; received in revised form 19 September 2006; accepted 20 October 2006
Abstract
An alternative approach to the process of selection and domestication of grain crops in early history based on nutritional value is proposed.
Selection by a long trial and error process among a number of wild large seeded legumes gave rise to a nutritionally superior domesticated
chickpea among the selected ‘‘founder crops’’ of the Neolithic Near Eastern agriculture. We found considerably higher free tryptophan levels
in cultivated stocks (44 desi and 29 kabuli types from 25 countries; 1.10 mg/g seed dry weight), compared with the wild progenitor Cicer reticulatum (15 accessions; 0.33 mg/g seed dry weight). Dietary tryptophan determines brain serotonin synthesis, which in turn affects certain brain
functions and human behaviour. We suggest that these nutritive facts may explain the decision of prehistoric farmers to choose this rare species
and struggle to keep such an agronomically complicated crop under domestication.
Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Chickpea; Legumes; Domestication; Neolithic; Nutritional
1. Introduction
About 11,000 years ago (before present; BP), humans
domesticated several plant species in the Near East and
harnessed them to their needs. Farming is thought to have
originated with a group of seven grain crops (diploid einkorn
wheat, tetraploid emmer wheat, barley, pea, lentil, chickpea,
bitter vetch) and flax (a fibre crop), the so called ‘‘founder
crops package’’ (Zohary and Hopf, 2000). Were the first
farmers able to distinguish favourable nutritious plants from
the wealth of species in their surroundings? The intuitive answer is probably yes, as evident from the dominant status of
* Corresponding author. Tel.: þ972 8 948 9278; fax: þ972 8 947 6189.
E-mail address: [email protected] (Z. Kerem).
0305-4403/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jas.2006.10.025
most of these ‘‘founder crops’’ in modern food production.
Surely, storage stability and taste were major nutritive determinants in the decision making of early farmers, similarly to
present day preferences. Dry chickpea seeds can be stored
from season to season similarly to cereals and other legumes
(e.g. wheat, barley or lentil). No perceptible taste changes occur under dry storage conditions, up to 52 weeks, and heat
treatment may even improve lipid stability and thereby storage
quality (Williams and Singh, 1987).
Plant domestication processes are traditionally discussed in
terms of the genetic changes related to breakdown of seed dispersal and seed dormancy, seed size and other plant characters
bearing on agronomic performance, both qualitative and quantitative, and on the profitability of farming operations (Abbo
et al., 2003; Harlan, 1992; Ladizinsky, 1998; Zohary, 1996).
However, data on the nutritional value of Near Eastern
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Z. Kerem et al. / Journal of Archaeological Science 34 (2007) 1289e1293
domesticants and its bearing on the domestication processes
was rarely presented, except perhaps for the inferior protein
content of domesticated tetraploid wheat relative to wild
emmer wheats (Avivi, 1978).
Chickpea domestication presents an interesting case to evaluate models of crop evolution. Although the founder crops are
traditionally considered as a coherent ‘‘agronomic package’’
(Zohary and Hopf, 2000), chickpea stands as an exception
among the wild progenitors of the founder grain crops and their
domesticated derivatives (Abbo et al., 2003). The distribution
of most wild progenitors of the founder crops is relatively
wide, extending through the Near East and West Asia, and in
part into Central Asia, while the wild progenitor of chickpea,
Cicer reticulatum Ladiz., is a rare species reported from only
several locations in south-eastern Turkey (37.3e39.3 N,
38.2e43.6 E) (Ladizinsky, 1995). Seed dispersal mode of
chickpea is also an exception among its companion Near Eastern grain legumes (Ladizinsky, 1980). Pod dehiscence is a typical feature of the wild progenitors of pea and lentil (Zohary and
Hopf, 2000), whereas in wild C. reticulatum pod dehiscence is
not an agronomic problem as most pods are retained intact at
full maturity (Ladizinsky, 1980). The cultivation of most
founder crops seems to have been relatively simple and did
not require sophisticated agro-techniques. Chickpea, again an
exception to this rule, was transformed into a summer crop
(thereby compromising 10 to 90% of its potential grain yield
as the result of water shortage, Abbo et al., 2003) probably already in Neolithic times. This transformation enabled farmers
to avoid the devastating effect of Ascochyta blight caused by
the fungus Didymella rabiei (Pass.) Lab., which may cause
total crop losses in winter (Abbo et al., 2003). This required
a supposedly long and quite inefficient selection for vernalization-insensitive types (Abbo et al., 2003), again an exception
among the accepted models for rather rapid domestication of
other Near Eastern crops (Zohary, 1996).
Why then was the rare and agronomically problematic
chickpea chosen to be among the initial crop assemblage,
a process mediated through the development of a novel agronomic practice, summer cropping, which may involve a considerable loss of the potential yield? In an attempt to
account for the domestication of the wild C. reticulatum and
its transformation into a summer crop we examined its nutritive value. Specifically, we determined in seeds of 88 wild
and domesticated chickpea accessions the levels and nutritional quality of total protein and of the limiting essential
amino acid (EAA) tryptophan, which has recognized effects
on human behaviour and is known to be perceived by animals
too (Ettle and Roth, 2004; Koopmans et al., 2005; Markus
et al., 2005).
harvested from plants grown in replicated experiments under
standard agronomic practice in the Faculty of Agriculture
farm in Rehovot Israel, under similar husbandry conditions.
Free tryptophan was extracted by microwave from individual ground seeds (Kerem et al., 2005). Total tryptophan was
determined in ground seeds after protein hydrolysis with
4.2 N NaOH. Tryptophan was analyzed by reversed-phase
chromatography (Allred and MacDonald, 1988). The LC analyses were carried out using a Spectra HPLC system with
Chromquest software (version 2.51), a pump (p4000), an autosampler (AS3000), and a diode-array detector (UV6000LP)
(Thermo Separation Products, San Jose, CA, USA). The separation was carried out on a LunaIIÔ ODS column (250 4.6 mm
I.D.) (Phenomenex, New York, NY, USA) with a guard column
(Phenomenex C-18, 1.0 4.6 mm I.D.).
Crude Protein was determined in ground seeds using block
digestion and Tecator KjeltecÔ Auto 2400 Analyzer e a modified Kjeldahl procedure with automatic distillation and titration (AOAC 976.06 (G) and (H)). Dry seed weight was
determined after oven drying at 60 C for 4 h (forced air).
3. Results
We surveyed a wide collection of chickpea cultivars (44
desi and 29 kabuli types from 25 countries), and compared
their seed features with the respective features of the wild progenitor (15 accessions). The mean seed weight of the wild
group does not differ from that of the desi group and both
desi and wild chickpea differ from kabuli chickpea (Fig. 1,
TukeyeKramer HSD, at alpha ¼ 0.05). Mean protein content
does not differ between the wild, desi and kabuli groups
(TukeyeKramer HSD, at alpha ¼ 0.05). In agreement with
the literature we found that chickpea seeds contain 5% oil,
65% carbohydrates, and 16 to 25% proteins. The total seed
protein content of the domesticated group (mean 19.41%,
18.62e20.22 (95% CL)) did not differ significantly from their
2. Materials and methods
Seeds of a wide collection of chickpea cultivars representing all major chickpea growing areas of the world (44 desi and
29 kabuli types) originating from 25 countries alongside 15
wild C. reticulatum accessions were employed in the chemical
analyses. All the seed material used for the analyses were
Fig. 1. The relationship between seed weight (gr) and the level of free tryptophan (mg/gr dry seed) in dry chickpea seeds (* wild Cicer reticulatum; B kabuli chickpea; C desi chickpea).
Z. Kerem et al. / Journal of Archaeological Science 34 (2007) 1289e1293
wild counterparts (18.59%, 17.53e19.64 (95% CL)). The cultivated group had 1.73 mg total tryptophan/gr dry seed, 1.58e
1.89 (95% CL), while the wild group had only 0.90 mg total
tryptophan/gr dry seed, 0.70e1.11 (95% CL). We found considerable amounts of free tryptophan in the seeds (mean of 73
cultivars 1.10 mg/gr dry seed, 1.03e1.17 e 95% confidence
limit (95% CL)). In comparison, among 15 wild C. reticulatum
accessions much smaller amounts of free tryptophan were
measured (mean of 0.33 mg/gr dry seed, 0.16e0.49 (95%
CL)). The two group means differ significantly (Student’s
t ¼ 8.7, with P(t) < 0.0001, 86 df).
Among the domesticated lines, the free tryptophan values
of the desi and kabuli accessions were similar (mean free tryptophan of desi cultivars 1.13 mg/gr dry seed, 1.03e1.23 (95%
CL), mean of the kabuli group 1.05 mg/gr dry seed, 0.93e1.18
(95% CL); P(t) ¼ 0.88. This observation is in line with the
known ancient status of the desi genepool and the more recent
emergence of kabuli chickpea (Ladizinsky, 1995). Both total
and free tryptophan in the two domesticated groups is similar
and both differ from the wild progenitor (Fig. 1, Tukeye
Kramer HSD, at alpha ¼ 0.05). Apparently there is no relationship between seed weight and free tryptophan content
both among wild and domesticated chickpea (Fig. 1). Interestingly enough, no such relationship is observed even within the
three analyzed groups (asterisks-wild, dots-desi, circleskabuli). Therefore, it is fair to discuss the results on the basis
of mg tryptophan per gr of dry seeds.
The nutritional quality of a protein is defined by its ability
to support growth in animals. ‘‘Chemical scoring’’ is a widely
accepted alternative approach to assign a quantitative value to
the pattern of amino acids in a particular dietary source, e.g.,
this assignment is based on the amounts and importance of
individual amino acids in a protein mixture. Typically, the limiting amino acids in dietary proteins are lysine, the sulphurcontaining amino acids (including methionine), threonine
and/or tryptophan. We have used tryptophan levels to calculate
the score of wild and domesticated chickpea protein using the
Food and Agriculture Organization/World Health Organization of the United Nations, amino acid requirement pattern
recommended for various age groups (EAA score, %; Table 1).
While a value greater than 100% is not commonly used, our
results suggest that tryptophan is the limiting EAA in wild
chickpea, especially during childhood. It is also shown that
tryptophan content in domesticated chickpea is significantly
higher, which indeed leaves methionine as the limiting amino
acid. Moreover, our results suggest that consuming domesticated chickpea will elevate the levels of tryptophan available
Table 1
Chemical scoring* of tryptophan in chickpea protein (%) based on the
presented average values in dry seeds
Cultivars
Children
(2e5 years)
Children
(10e12 years)
Adults
Wild
Domesticated
44
81
54
99
97
178
*
Based on the presented average values in dry seeds.
1291
for processes other than growth and maintenance, e.g., biosynthesis of brain serotonin.
To test the possible effect of processing chickpea grain for
human consumption on the levels of tryptophan (free or total)
we have run grinding/pounding, soaking in water (overnight),
and boiling treatments. These processes may induce oxidation
(tryptophan may act as a reducing agent), degradation or Maillard reactions (a chemical reaction between an amino acid, including tryptophan, and a reducing sugar, usually requiring the
addition of heat, and resulting in the loss of the amino acid).
However, using high tryptophan kabuli grains, we found that
the total protein, the total and free tryptophan levels did not
decrease in any of these processing treatments.
4. Discussion
Selection for higher tryptophan levels among crop varieties
was entirely dependent upon prehistoric humans’ ability to
recognize naturally occurring variability in this trait. It is clear
that intact protein can have a potent satiety-triggering effect,
but in addition, specific amino acids or peptides could also exert a noticeable action. Indeed, certain amino acids such as
phenylalanine or tryptophan were shown to increase satiety
and also adjust food preferences in humans (Hill and Blundell,
1988). A similar pattern of selection ability is recognized in
farm animals (Eder et al., 2001), and diets enriched with tryptophan were recently shown to induce accelerated growth
(Eder et al., 2001, 2003; Ettle and Roth, 2004; Henry et al.,
1992).
Tryptophan is a precursor of serotonin (5-hydroxytryptamine, 5-HT) in the brain (Fernstrom and Fernstrom, 1995).
Increasing dietary tryptophan content is accompanied by increased plasma tryptophan, which in turn leads to a higher
brain serotonin concentration. To reach the brain, plasma tryptophan competes with other plasma Large Neutral Amino
Acids (LNAA; isoleucine, leucine, valine, phenylalanine, tyrosine) for transport across the brain blood barrier. Thus, plasma
tryptophan/LNAA ratio determines the amount of tryptophan
that reaches the brain: a high ratio allows for enhanced tryptophan transport into brain tissue (Fernstrom and Fernstrom,
1995; Leibowitz and Alexander, 1998). Also, insulin induces
the transfer of LNAA into muscle tissues in adult humans who
consume a mixed diet high in carbohydrates. This effect increases
the plasma tryptophan/LNAAs ratio thus enhancing the transfer
of tryptophan into the brain (Fernstrom and Wurtman, 1971;
Leibowitz and Alexander, 1998; Wurtman et al., 2003). Plasma
tryptophan/LNAA ratio was also shown to regulate the sleepwake rhythm in infants and adults (Steinberg et al., 1992). The importance of tryptophan is further indicated by data suggesting that
newborns and infants may be at risk of insufficient bioavailability
of tryptophan for optimal serotonin synthesis in the brain (Heine,
1999).
Ample data indicates that high brain serotonin induces satiety (Leibowitz and Alexander, 1998). Manipulating serotonin
levels (through an increase of dietary tryptophan intake) may
increase pulsatile secretion of the luteinizing hormone in the
monthly hormone cycle leading to ovulation of normal
Z. Kerem et al. / Journal of Archaeological Science 34 (2007) 1289e1293
1292
women, and also in animal models. Thus, higher ovulation
rates may be an outcome of increasing dietary tryptophan.
Plasma tryptophan levels may decrease following lactation
in women, leading to decreased ovulation rates (Downing
et al., 1997; Lado-Abeal et al., 1997), and increased demand
for tryptophan.
Serotonin is also implicated in cognitive ability and impulsivity (Clarke et al., 2004), while tryptophan depletion in humans has little effect on the performance of tasks activating
the dorsolateral region of the prefrontal cortex, such as spatial
working memory or planning (Park et al., 1994). Thus, tryptophan availability may affect cognitive performances related to
social behaviour and emotional processing, especially under
stress (Lieberman, 2003). This effect implicates tryptophan
in lowering of aggression and promotion of receptivity, and
thus dominant behaviour and decreased quarrelsomeness in
healthy (human) volunteers (Moskowitz et al., 2003).
What daily amount of chickpea seeds need be consumed to
account for tryptophan requirement? We have used the recommended daily allowance values of tryptophan for various age
groups, based on its levels in wild and domesticated
seeds (Table 2). Our results demonstrate that as a tryptophan
source in childhood, the domesticated chickpea is almost twice
as good as the wild progenitor.
Large seeded legumes were part of the human diet long
before the Neolithic agricultural revolution as evident from
archaeobotanical finds from the Mousterian layers of Kebara
Cave (Lev et al., 2005). Several species of large seeded legumes were recovered from Neolithic layers throughout the
Levant (Moore et al., 2000; Zohary and Hopf, 2000). The earliest evidence for domesticated chickpea is from Neolithic
sites around 10,500 cal BP. We cannot determine the timing
of the increase in chickpea seed tryptophan. However, it
should be borne in mind that the wide array of large seeded
legume species that were utilised in the Near East were natural
candidates for cultivation and domestication. We assume that
processes of trial and error with such large seeded legumes
have taken place prior to the appearance of a high tryptophan/LNAA mutant in cultivated fields. The rarity of wild
Cicer reticulatum (especially compared with the common
wild lentil and wild pea), and the agronomic difficulties
(Abbo et al., 2003) involved in chickpea cropping call for an
unorthodox explanation for the motivation to retain chickpea
as a crop plant. We propose that the significant increase in
the levels of free (and total) tryptophan occurred following
the selection process under cultivation. This, in turn, enriched
Table 2
Daily intake of chickpea (gr) to account for recommended daily allowance
values of tryptophan published by FAO/WHO, based on the presented average
values in dry seeds
Cultivars
Children
(2e5 years)
Children
(10e12 years)
Adults
Wild
Domesticated
13
7
3
2
4
2
*Recommended daily allowance values published by FAO/WHO16. **Based
on the presented average values in dry seeds.
the diet of the early farmers and made chickpea a unique food
source. The profound effects of tryptophan-enriched diet
(above) may help answer the questions raised concerning the
difficulties of bringing chickpea under domestication. In our
view, these effects provide a reasonable explanation for the insistence of the Neolithic farmers to retain chickpea under cultivation and develop new agro-techniques to ensure stable
yields (Abbo et al., 2003) which eventually brought it to its
current global status as the third in importance grain legume.
It is tempting to relate the above survey of the physiological
and behavioural effects of increased tryptophan consumption
to the newly established Neolithic system and we offer several
provocative points.
An enriched tryptophan diet brings about higher ovulation
rates and thus better prospects for more frequent births e an
important factor in a time of demographic growth such as
the Neolithic era (e.g., Eshed et al., 2004; Hassan, 1981;
Hershkovitz and Gopher, 1990). Enriched tryptophan diet
also improves infant development and daily scheduling by inducing satiety and thus prolonging the gaps between meals and
sleepiness; a high tryptophan intake improves performance
under stress and increases distinction ability in the social
sphere which may relate to sedentism and increased social tension under sedentary conditions of larger scale populations
(Hodder, 2001); it promotes dominance in an era of decreasing
egalitarianism and increasing social complexity; it promotes
an investigative behaviour in an era of invention, innovation
and socio-economic change (e.g., Cauvin, 2000); and it promotes increased self confidence and acts as an anti-depressant
that could have been a significant attribute in a dynamic time
such as the Neolithic period.
Unlike suggestions that farming was initially based on low
valued sources (e.g., Rindos, 1984; Weiss et al., 2004),
it seems that the inclusion of chickpea in the founder crop
package is best understood in light of its high nutritional
seed properties. The crop packages adopted in the Near
East, Meso-America, Sub-Sharan Africa and East Asia, all include cereal and grain legumes. Apparently, the complementary nutritional contents of cereal and legume seeds was
taken for granted by the students of plant domestication, and
nutritional value changes associated with domestication were
given little attention.
Some models relate the adoption of crop plants, at least
partly, to a random/chance process like the so called ‘‘dump
heap’’ hypothesis (e.g., Hawkes, 1977; Sauer, 1952). This concept sees plant domestication as a process driven by anthropogenic ecological disturbance that opened the way for ‘‘camp
follower’’ plants that attracted the attention of food gatherers.
However, the biology of the wild progenitors of the Near Eastern crops suggests that this was not the case (Abbo et al.,
2005). In our view, the selection of candidates for cultivation
was, extremely wise and based on rich/deep floristic and ecological knowledge. It also focused on a small number of plants
out of a wide array of available plant resources and it required
long processes of trial and error. For example, this meticulous
selection included certain problematic/difficult species such as
the low producing lentil and the patchy distributed pea. The
Z. Kerem et al. / Journal of Archaeological Science 34 (2007) 1289e1293
chickpea presented here, with its very specific agronomic
needs, we suggest, was selected following considerations presented above of which the awareness to nutritional aspects was
a major consideration. This however does not rule out the possibility that higher tryptophan level was associated with selection to an additional agronomically important phenotype in the
incipient farmers’ fields.
In retrospect, the best testimony for the sophisticated choice
of early cultivators is the dominant status of these grain crops in
food production throughout history to this very day. Moreover, it
seems that the choice of chickpea (among other crops) should
not be seen as a direct response to stress (promoting intensified
resource extraction). It should rather 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
into the ever-growing human cultural niche.
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