Spatial Adaptations for Plant Foraging: Women Excel and Calories Count
We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources. In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate that a simple but ecologically important shift in content can reverse this sex difference. This effect is predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for gathering-specific spatial mechanisms, some of which are sexually differentiated. The hypothesis that gathering-specific spatial adaptations exist in the human mind is further supported by our finding that spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density). This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efficient foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain specific and designed by natural selection to mesh with important regularities of the ancestral world.
Spatial adaptations for plant foraging: women
excel and calories count
, Max M. Krasnow
, Danielle Tr uxaw
and Steven J. C. Gaulin
Department of Psychology, Yale University, 2 Hillhouse Avenue, New Haven, CT 06520-8205, USA
Department of Psychology, and
Department of Anthropology, University of California, Santa Barbara, CA 93106-9660, USA
We present evidence for an evolved sexually dimorphic adaptation that activates spatial memory and
navigation skills in response to fruits, vegetables and other traditionally gatherable sessile food resources.
In spite of extensive evidence for a male advantage on a wide variety of navigational tasks, we demonstrate
that a simple but ecologically important shift in content can reverse this sex difference. This effect is
predicted by and consistent with the theory that a sexual division in ancestral foraging labour selected for
gathering-speciﬁc spatial mechanisms, some of which are sexually differentiated. The hypothesis that
gathering-speciﬁc spatial adaptations exist in the human mind is further supported by our ﬁnding that
spatial memory is preferentially engaged for resources with higher nutritional quality (e.g. caloric density).
This result strongly suggests that the underlying mechanisms evolved in part as adaptations for efﬁcient
foraging. Together, these results demonstrate that human spatial cognition is content sensitive, domain
speciﬁc and designed by natural selection to mesh with important regularities of the ancestral world.
Keywords: foraging adaptations; sex differences; optimal foraging theory; spatial cognition; navigation
Spatial cognitionin humans is not a unitary faculty (Halpern
2000); rather, it seems to reﬂect the operation of a number of
functionally distinct (and neurally dissociable) cognitive
specializations, each designed for solving a different adaptive
problem. The selection pressures shaping some of these
specializations would have been similar for ancestral men
and women, producing sexually monomorphic compu-
tational design. In certain cases, however, ancestral men and
women would have faced distinct spatial demands; in these
cases, we should ﬁnd that the resultant cognitive
mechanisms are sexually dimorphic.
Such sex differences are well documented in the existing
literature on human spatial abilities. Spatial tasks exhibit
some of the largest and most reliable sex differences in
cognitive performance. On many spatial tasks, male
advantage is typical (Linn & Petersen 1985; Voyer et al.
1995) and these ﬁndings have often been used to conclude
that men have superior spatial ability (Linn & Petersen
1985). Using an evolution-minded approach, however,
Silverman & Eals (1992) predicted and documented a
speciﬁc female advantage. Their foraging adaptation theory
argues that hunting mobile prey and gathering immobile
resources have different computational requirements; to the
extent that the universal sexual division of foraging labour
among described hunter–gatherers (Murdock 1967)
characterized our ancestral past, sexually dimorphic fora-
ging-related cognitive specializations should be observable
in the minds of modern men and women.
According to this foraging adaptation theory, many of
the spatial tasks that presently show a male advantage
engage cognitive mechanisms designed by natural selec-
tion for successful hunting. In hunting, mobile prey are
pursued over erratic and unpredictable courses often
through unfamiliar environments; given the energetic
costs of transport, the spoils should be carried home via
a more direct route, a task that can be accomplished by
vector integration (Gallistel 1990) or from vector compu-
tation within a survey representation of the environment.
Past tests of navigating and wayﬁnding (Moffat et al. 1998;
Sandstrom et al. 1998; Lawton & Morrin 1999; Silverman
et al. 2000; Malinowski 2001), as well as some laboratory
tasks such as mental rotation (Linn & Petersen 1985;
Voyer et al. 1995), may elicit a male advantage by engaging
spatial mechanisms that evolved for this kind of navigation
The spatial problems posed by gathering are quite
different. Gathered resources are stationary and vary in
quality and availability with time—a ﬁg tree may have
nothing valuable now but be laden with fruit in the near
future. To relocate diverse resources as they become valuable
requires a mechanism that registers and stores the locations
of many stationary food resources within a survey map of a
more constrained and well-known environment. A well-
designed adaptive specialization for gathering would
accumulate such information automatically, without special
attention, during daily activities. Silverman & Eals (1992)
argued that, if a sexually dimorphic spatial adaptation for
gathering exists, women should excel at remembering the
locations of items within a complex spatial array, especially
in incidental learning tasks.
Silverman and Eals operationalized these skills as
‘object-location memory’ and devised a number of
pencil-and-paper and desktop tasks to assess it. The
predicted female advantage has sometimes been demon-
strated on these tasks, but the effect is sensitive to details of
task presentation, sometimes appearing robustly and
sometimes disappearing entirely (Eals & Silverman
1994; James & Kimura 1997; Dabbs et al. 1998; see
Postma et al. 2004 for a review). Arguably, some of these
Proc. R. Soc. B (2007) 274, 2679–2684
Published online 21 August 2007
* Author for correspondence (email@example.com).
Received 19 June 2007
Accepted 2 August 2007
2679 This journal is q 2007 The Royal Society
effects are theory relevant (e.g. larger female advantage in
incidental than directed learning tasks), but others are
more difﬁcult to interpret (e.g. no female advantage for
difﬁcult-to-name objects), leaving their experimental
demonstration vulnerable to alternative interpretations.
Such fragile effects may be a consequence of using
experimental tasks that only weakly engage spatial
adaptations for plant foraging. Put another way, the
division-of-labour model has not been effectively tested
because the scale (8.5
or desktop), content (e.g.
household items or machine parts) and task (did the item
move?) do not match the scale (walking), content
(immobile foods) and task (which way to the mongongo
nut grove?) of real-world plant foraging. Thus, a stronger
female advantage should be observed on a spatial task that
better approximates the ancestral conditions of plant
foraging: speciﬁcally, a task that provides both the cues
appropriate to engage the hypothesized mechanism and
the kind of information it is designed to process (i.e. the
content and location of nutritional resource patches). No
prior investigation has tested whether women demonstrate
superior spatial memory for food resource locations at a
In this study, we employed the scale, spatial complexity
and item diversity of a large farmers’ market to assess
memory for the location of immobile food resources such
as leaves, fruits, nuts, roots and honey. If the Silverman
and Eals’ hypothesis is correct, then
: Females will remember the locations of such food
resources more accurately than men.
In general, women prefer to navigate by landmarks and
routes, rather than by vectoring (Halpern 2000), and a
methodology that emphasized route- and landmark-based
strategies might well have produced a female advantage.
However, our intention was not to replicate these well-
known sex differences, but to test for a predicted content
effect: females more accurately recalling the location of
immobile foods. Thus, in order to most effectively jeopardize
this hypothesis, we designed our study to favour men’s
established wayﬁnding strengths. To this end, participants
were tested in a newly learned and directly experienced
environment (Montello et al.1999), were not explicitly
oriented to any landmarks during exposure (Baenninger
1997) and were tested via pointing to the non-visible
resource locations (Hegarty et al. 2006)—a vectoring
measure that advantages the orientation strategy favoured
by men and disadvantages the route strategy typically
favoured by women (Lawton 1994). It is possible that
such a design might obscure any actual female advantage.
However, effective plant foragers would require the ability to
ﬂexibly integrate various navigation strategies as dictated by
their nutritional needs and patterns of resource availability.
Thus, we predict that women will also be able to form survey
representations and estimate vectors to resource locations.
To test for this ability, participants were tested at a central
off-route location via pointing, a measure that minimizes the
possible employment of route- and landmark-based
strategies for responding. A female advantage on such a
task would be strong evidence for a foraging-related
The suite of cognitive skills labelled ‘spatial abilities’
most likely arose from selection pressures in a number of
domains (e.g. searching for nutrients, searching for mates;
Hewlett et al. 1986; Gaulin & FitzGerald 1989) and
subdomains (e.g. searching for food versus searching for
water; Petrinovich & Bolles 1954). Thus, although we
predict a female advantage on resource location memory,
some foraging-related selection pressures may have
impinged similarly on ancestral males and females. For
example, optimal foraging theory (Schoener 1971)
addresses the mechanisms that underlie dietary choice.
Such theories assume that foragers are capable of assessing
the ‘proﬁtability’ of potential food items as a basis for
eating or rejecting them and have been validated on
human foragers ( Winterhalder & Smith 2000). This
assumption justiﬁes a collateral prediction:
: The locations of more nutritionally valuable resources
will be more accurately remembered than less nutritionally
Such a bias would support the argument that the
mechanisms underlying resource location memory are
adaptations for foraging.
2. MATERIAL AND METHODS
Data were collected during the spring and summer of 2004 at
six separate meetings of the Saturday morning farmers’
market in Santa Barbara, California. The market comprises
10 orderly rows of vendors laid out in a rectangular 0.6 ha
area. There were typically approximately 90 food stalls.
Eighty-six adults (41 females; mean age, 35 years) participated
in this experiment. Data from 18 additional participants were
discarded due to participant attrition, food running out at a
target location or experimenter error during the task.
Participants were recruited near an entrance to the
farmers’ market and told that they could earn $10 (or $5
and a UCSB tote bag) by participating in ‘farmers’ market
research’. This cover story—which does not refer to any
spatial task—was used to ensure that the encoding of resource
locations would be strictly incidental. All participants were
given a consent form on which they were asked to indicate
food allergies. Participants were then asked their age and how
frequently they visited this farmers’ market. The answers to
these questions were recorded by the experimenter, who also
made note of each participant’s sex.
(b) Materials and procedures
Participants were led by a circuitous route to each of six food
stalls, where they were given a food item to eat. The precise
food items, stalls and routes were ﬁxed on any given day of
data collection but varied over the 6 days. Within each day,
subjects were assigned equally to the ‘forward’ and ‘reversed’
versions of the ﬁxed route (table 1 for food items and orders).
At each stall, participants were asked a set list of questions
which served in part to promote the cover story and were also
analysed as possible predictors of pointing accuracy:
(i) ‘On a scale of 1–7, how much do you like the taste
(ii) ‘On a scale of 1–7, how often do you eat this?’
(iii) ‘On a scale of 1–7, how attractive do you think this
(iv) ‘How many times have you purchased from this stall?’
2680 J. New et al. Foraging adaptations: spatial cognition
Proc. R. Soc. B (2007)
Experimenters recorded participants’ answers.
After visiting all six stalls, participants were taken to a
pointing device in the centre of the market area. The pointing
device was a ﬂat, horizontal, circular board of 30 cm in
diameter mounted on a camera tripod and located such that
all of the visited stalls were obscured from view. The board
was marked radially in 18 increments. A wooden pointer was
ﬁxed at the centre of the circle and could be spun freely.
Participants were asked to aim the pointer at each of the six
food items in one of two predetermined orders that differed
from both presentation orders. The experimenter recorded
the indicated bearing for each food item.
Participants then were asked to assess their general sense of
direction on a 1–7 scale, a measure known to be correlated with
ﬁeld measures of navigational ability (Kozlowski & Bryant
1977; Sholl 1988; Montello & Pick 1993; Prestopnik &
Roskos-Ewoldson 2000; Sholl et al.2000). Participants were
then offered information about the background and rationale of
the study and were ﬁnally taken back to the farmers’ market
entrance to receive payment.
(a) Analytical methods
Pointing error, our inverse estimate of accuracy of food
location memory, was measured in degrees as the smallest
difference between each participant’s estimate and the true
bearing to each of the six food locations. Errors, therefore,
ranged from 08 (perfect accuracy) to 1808 (opposite from
correct direction), with 908 indicating chance performance
(Sholl et al.2000). Smaller errors indicate greater accuracy.
To test our hypotheses, we modelled pointing error in a
two-level hierarchical linear model (HLM) with individual
pointing errors as ﬁrst-level observations and participants as
second-level observations (following the random coefﬁ-
cients method described in Raudenbush & Bryk 2002).
As ﬁrst-level predictors, we entered caloric density
(kcal 100 g
, an estimate of nutritional value; USDA,
no date http://www.nal.usda.gov/fnic/foodcomp/search/)
which we log-transformed to correct for a strong negative
skew, as well as the participants’ four ratings of the pointed-
to foods and stalls ((i)–(iv)). As second-level predictors we
entered participant sex, as well as their number of weekly
visits to the market, their self-rated sense of direction and a
rank variable reﬂecting differences among weeks in the
difﬁculty of the test environment. (Stalls and routes differed
from week to week, leading to differences in weekly average
error; including this variable allowed us to separate these
theory-irrelevant differences from the effects of interest.)
: Are women more accurate than men at
pointing to newly learned food locations?
Yes. Women were, on average, 98 more accurate in their
pointing estimates than men (gZK8.917, t(80)Z2.454,
pZ0.017). This corresponds to a 27% improvement in
performance compared with men.
This female advantage in accuracy was not due to
women having more experience at the farmers’ market
than men. Experience at the market did not predict
performance, either as a zero-order effect or in the HLM
model (table 2, between-subjects effects). The female
Table 1. Weekly items, routes and descriptive statistics. (Food items used over the course of the 6 day experiment are listed
below. Item number indicates the order in which participants were led to each food item. Half of the participants were led around
in the ‘forward’ direction, as indicated by the ﬁrst number listed. The other half of the participants were led around in the
‘backward’ direction, as indicated by the second number, listed in parentheses.)
item number 1 2 3 4 5 6
1 (6) cherries oranges olive oil fennel basil strawberries
2 (5) sugar peas cherimoya peaches blueberries peaches plums
3 (4) honey almonds radish sprts apples tangerines carrots
4 (3) tomatoes basil cauliﬂower peaches strawberries cucumbers
5 (2) almonds rd lf lettuce cherries zucchini peppers green onion
6 (1) cherimoya avocado zucchini olive oil zucchini tangerines
n(F : M) 9(5 : 4) 15(7 : 8) 17(8 : 9) 17(6 : 11) 6(4 : 2) 22(11 : 11)
raw error (s.d.) 28.978 (13.91) 27.908 (19.36) 30.788 (13.93) 25.178 (12.72) 22.958 (7.58) 48.318 (17.71)
Table 2. Pointing error: hierarchical linear model (with robust standard errors).
effect coefﬁcient s.e. t d.f. p
intercept 32.891 1.786 18.414 80 1.68!10
sex K8.917 3.634 K2.454 80 0.017
sense of direction K3.737 1.276 K2.928 80 0.005
week rank 2.699 1.389 1.943 80 0.055
experience K0.952 1.129 K0.843 80 0.402
log(kcal) K14.309 3.030 K4.722 478 3.07!10
food liking K0.275 0.794 K0.347 478 0.729
food eat often 1.380 0.790 1.747 478 0.081
stall liking K0.903 1.105 K0.817 478 0.415
stall shop often 0.018 0.175 K0.104 478 0.918
Foraging adaptations: spatial cognition J. New et al. 2681
Proc. R. Soc. B (2007)
advantage is signiﬁcant even after controlling for experi-
ence at the market.
Did this female advantage arise because our sample was
composed of women who are unusually gifted at navigation?
No. The sense of direction measure has been shown to be a
good index of one’s general ability to navigate and, as in prior
research, there was a male advantage on this measure
2.68, pZ0.009, two-tailed, dZ0.58). Internal evidence
conﬁrms the ecological validity of this self-report measure: it
predicted unique variance in pointing accuracy for both
sexes (gZK3.737, t(80)Z2.928, pZ0.005).
Clearly, a male advantage in general sense of direction
cannot explain a female advantage in pointing accuracy on
our task. Importantly, the female advantage in vectoring
towards food items was independent of this general ability:
it remains after controlling for sense of direction.
Weekly differences in the difﬁculty of test conditions did
explain unique variance in pointing accuracy (gZ2.699,
t(80)Z1.943, pZ0.055), but the unique contribution of
sex remains even after controlling for this and all other
: Do people remember the locations of
higher-quality foods more accurately?
Yes. Foods with higher caloric density were pointed to more
accurately by both sexes (gZK14.309, t(478)Z4.722,
). Since small errors indicate greater
accuracy, this relationship manifests as a negative corre-
lation: high caloric density predicts low pointing errors.
This effect was not due to subjects preferring the taste of
high over low caloric density foods. How much subjects liked
the taste of each food did not correlate with pointing
accuracy, even as a zero-level effect. In contrast, the effect of
caloric density on pointing accuracy remained signiﬁcant
even after controlling for how much subjects liked the taste
of each food, how often they eat each food, how attractive
they found the stall selling the food, and how often they had
purchased food from that stall. Indeed, none of these other
variables made a zero-order or unique contribution to
performance (table 2, within-subjects effects).
The greater accuracy in locating high-calorie food
items could conceivably have been driven by some other
property confounded with caloric density in our sample of
foods. For example, several of the highest calorie items
might also be considered non-standard for other reasons
(people rarely drink olive oil; olive oil and honey are
liquids whereas the other items are countable objects,
etc.). To account for this general class of alternative
hypotheses, we replicated the HLM analysis after omitting
data for the four highest calorie items (olive oil, almonds,
honey and avocados). An inspection of ﬁgure 1 indicates
that the negative correlation between caloric density and
pointing accuracy is actually stronger below 2 log(kcal)
than above, and despite the loss in power due to a
restricted sample, the calorie/accuracy relationship is still
signiﬁcant when these items are removed.
A different and simpler approach to analysing these data
is to use food items as the unit of analysis, averaging across all
participants’ pointing errors to a given item. This allows one
to test for a relationship between average pointing accuracy
elicited by each food and predictor variables. In this case,
log-transformed caloric density of the food item as well as the
four average ratings of the foods and stalls were regressed on
the average pointing errors. As in the HLM analysis, foods
with higher caloric densities were pointed to more accurately
(bZK0.519, t(25)Z2.849, p!0.01; ﬁgure 1). This effect
was constant across women and men in both the HLM and
item-wise analyses (z’s!0.451, n.s.). As in the HLM,
participants did not point more accurately to foods that were
more liked or eaten more often, nor to stalls that were liked
more or shopped at more often (b’sOK0.180, t’s(25)!
Thus, in accordance with the prediction that the
farmers’ market context would activate adaptations that
evolved for foraging, foods higher in nutritional quality
were pointed to more accurately. Importantly, nutritional
quality was the only variable to independently predict
b = –0.519**
pointing error (deg.)
(error bars indicate ± 1 s.e.)
1.0 1.5 2.0
a – tomato
b – cauliflower
c – green onion
d – plum
e – basil
f – peaches
g – sugar peas
h – strawberry
i – radish sprouts
j – tangerine
Figure 1. Item-wise plot of mean error (Gs.e.) by (log) caloric density.
2682 J. New et al. Foraging adaptations: spatial cognition
Proc. R. Soc. B (2007)
variance in pointing accuracy; indeed, liking, familiarity,
experience and other variables were not signiﬁcantly
correlated with pointing accuracy.
Silverman & Eals (1992) argue that the female advantage
on pencil-and-paper and desktop measures of object-
location memory reﬂects a selective pressure on ancestral
women for plant-foraging efﬁciency. But their measures
did not involve foods, tested spatial memory on a very
small scale, and included no measure of vectoring; as a
result, a female advantage on their measures is open to
many alternative interpretations. For this reason, we
deemed it important to examine whether a female
advantage could be demonstrated on a task that closely
resembles foraging for plant foods. From this theory, we
predicted that women should remember the locations
where they have previously encountered immobile
resources (e.g. plants, honey) more accurately than do
men. This is a counter-intuitive hypothesis. Accurate
performance on our pointing task requires vectoring
locations—the type of spatial representation more often
(Lawton 1994) and more proﬁciently (Saucier et al. 2002)
employed by men. Although prior research suggests that
men are frequently better at pointing to the locations of
landmarks and other non-food objects under such
circumstances, we have shown that women are better
than men at pointing to spatial locations that contain
nutritional resources. That navigational tasks requiring
vector integration (dead reckoning) show a male advan-
tage when the ‘landmarks’ are not food makes the present
ﬁnding of a female advantage all the more compelling and
offers less ambiguous novel support for the idea that
ancestral sex differences in foraging behaviour may have
shaped sex-speciﬁc cognitive adaptations.
Given that females are often the primary shopper for
household goods ( Fram & Axelrod 1990), for example,
constituting 73% of the food shopping respondents in a
1992 consumer research study (IMRA 1992), it is
reasonable to question whether the general shopping
environment or context, rather than the food items per se,
provided the cues that enhanced female performance.
However, past research indicates that females are no better
than men at learning generic item locations in real-world
shopping locations (Kirasic 2000), nor pointing to the
locations of unseen vendors, even when they were more
familiar with the shopping centre (Dogu & Erkip 2000).
More recently, males were generally better in learning the
spatial layout of a simulated shopping centre ( Tlauka et al.
2005). This research suggests that females’ greater
experience with typical shopping layouts themselves, or
other aspects of the shopping context, did not account for
their more accurate performance in the present study.
Against the background of prior research on spatial
learning in shopping environments, the present results
suggest that it was the food items that provided the cues
which preferentially engaged female location memory.
The ﬁnding that nutritional quality enhances spatial
memory further supports the idea that our task is engaging a
foraging-related spatial adaptation. Interestingly, spatial
memory performance was not explicable in terms of
consciously mediated and articulated preferences for the
food items or their presentation. From the perspective of
current theory in behavioural ecology, the registration of
potential foods’ relative nutritional values is a central
requirement for optimally gathering foods from dispersed
and varying locations (Schoener 1971). Thus, the more
accurate localization of high-calorie food items (and not
those explicitly preferred) appears to reﬂect the priorities of a
psychological mechanism which was adapted for the
efﬁcient exploitation of plant foods during the 99.7% of
human evolution when our ancestors were foragers. This
result strongly indicates a cognitive system with ﬁne-tuned
dimensions of valuation (e.g. caloric density) built into its
architecture and should encourage the further development
of models of cognition that incorporate ecologically valid
valuation as a computational element (To o b y et al. 2005).
We gratefully thank Leda Cosmides, Tamsin German and the
members of the CEP and SCRAM groups at UC Santa Barbara
for their feedback on earlier drafts of this manuscript and
Nancy Collins for invaluable statistical advice. Additionally, we
thank the vendors and staff of the Santa Barbara Certiﬁed
Farmers Market Association for their assistance and patience
during our study. Finally, we thank our team of research
assistants who pitched in so many hours collecting data with us.
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