Baby falls while walking: We propose that a system that discounts the impact of errors in early stages of development encourages infants to practice basic skills such as walking to the point of mastery

The impact of errors in infant development: Falling like a baby. Danyang Han  Karen E. Adolph. Developmental Science, December 5 2020. https://doi.org/10.1111/desc.13069

Abstract: What is the role of errors in infants' acquisition of basic skills such as walking, skills that require immense amounts of practice to become flexible and generative? Do infants change their behaviors based on negative feedback from errors, as suggested by “reinforcement learning” in artificial intelligence, or do errors go largely unmarked so that learning relies on positive feedback? We used falling as a model system to examine the impact of errors in infant development. We examined fall severity based on parent reports of prior falls and videos of 563 falls incurred by 138 13‐ to 19‐month‐old infants during free play in a laboratory playroom. Parent reports of notable falls were limited to 33% of infants and medical attention was limited to 2% of infants. Video‐recorded falls were typically low‐impact events. After falling during free play in the laboratory, infants rarely fussed (4% of falls), caregivers rarely showed concern (8% of falls), and infants were back at play within seconds. Impact forces were mitigated by infants' effective reactive behaviors, quick arrest of the fall before torso or head impact, and small body size. Moreover, falling did not alter infants' subsequent behavior. Infants were not deterred from locomotion or from interacting with the objects and elevations implicated in their falls. We propose that a system that discounts the impact of errors in early stages of development encourages infants to practice basic skills such as walking to the point of mastery.

Modern women show signs of the ancestral competition among women, disliking & aggressing against those who threaten their romantic prospects, targeting especially physically attractive & sexually uninhibited peers

Our Grandmothers’ Legacy: Challenges Faced by Female Ancestors Leave Traces in Modern Women’s Same-Sex Relationships. Tania A. Reynolds. Archives of Sexual Behavior, Jan 4 2021. https://rd.springer.com/article/10.1007/s10508-020-01768-x

Abstract: Investigations of women’s same-sex relationships present a paradoxical pattern, with women generally disliking competition, yet also exhibiting signs of intrasexual rivalry. The current article leverages the historical challenges faced by female ancestors to understand modern women’s same-sex relationships. Across history, women were largely denied independent access to resources, often depending on male partners’ provisioning to support themselves and their children. Same-sex peers thus became women’s primary romantic rivals in competing to attract and retain relationships with the limited partners able and willing to invest. Modern women show signs of this competition, disliking and aggressing against those who threaten their romantic prospects, targeting especially physically attractive and sexually uninhibited peers. However, women also rely on one another for aid, information, and support. As most social groups were patrilocal across history, upon marriage, women left their families to reside with their husbands. Female ancestors likely used reciprocal altruism or mutualism to facilitate cooperative relationships with nearby unrelated women. To sustain these mutually beneficial cooperative exchange relationships, women may avoid competitive and status-striving peers, instead preferring kind, humble, and loyal allies. Ancestral women who managed to simultaneously compete for romantic partners while forming cooperative female friendships would have been especially successful. Women may therefore have developed strategies to achieve both competitive and cooperative goals, such as guising their intrasexual competition as prosociality or vulnerability. These historical challenges make sense of the seemingly paradoxical pattern of female aversion to competition, relational aggression, and valuation of loyal friends, offering insight into possible opportunities for intervention.

Supposedly, having multiple non-marital sex partners reduces traditional incentives for men to get married; instead, recent sex partners reduce the odds of marriage, but the lifetime number of non-marital sex partners does not

Wolfinger, Nicholas H., and Samuel Perry. 2021. “Does Promiscuity Affect Marriage Rates?.” SocArXiv. January 4. doi:10.31235/osf.io/n9e6p

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346329239063293952

Abstract: Sociologists have proposed numerous theories for declining marriage rates in the United States, generally highlighting demographic, economic, and cultural factors. One controversial theory contends that having multiple non-marital sex partners reduces traditional incentives for men to get married and simultaneously undermines their prospects in the marriage market. For women, multiple partners purportedly reduces their desirability as spouses by evoking a gendered double-standard about promiscuity. Though previous studies have shown that having multiple premarital sex partners is negatively associated with marital quality and stability, to date no research has examined whether having multiple non-marital sex partners affects marriage rates. Data from four waves of the National Survey of Family Growth reveal American women who report more sex partners are less likely to get married (though so too are virgins). Yet this finding is potentially misleading given the retrospective and cross-sectional nature of the data. Seventeen waves of prospective data from the National Longitudinal Survey of Youth’s 1997 mixed-gender cohort that extend through 2015 show that more non-marital sex partners has a temporary effect on marriage rates: recent sex partners reduce the odds of marriage, but the lifetime number of non-marital sex partners does not. Seemingly unrelated bivariate probit models suggest that the short-term effect is likely causal. Our findings ultimately cast doubt on recent scholarship that has implicated the ready availability of casual sex in the retreat from marriage. Rather, the effect of multiple sex partners on marriage rates is “seasonal” for most Americans.

A 44-year-old woman started to ask whether her family had attended her funeral; since she thought she had died, she told her husband to marry another woman

Cotard syndrome in anti-NMDAR encephalitis: two patients and insights from molecular imaging. J Ramirez Bermudez et al. The Neural Basis of Cognition, Jan 4 2021. https://doi.org/10.1080/13554794.2020.1866018

Rolf Degen's take: https://twitter.com/DegenRolf/status/1346129241281339398

Abstract: Cotard syndrome is a clinical condition defined by the presence of nihilistic delusions. We report two patients with Cotard syndrome in whom anti-NMDAR encephalitis (ANMDARE) was confirmed. Both cases showed features of affective psychosis, developed catatonic syndrome, and worsened after the use of antipsychotics. 18F-FDG PET brain studies showed a bilateral hemispheric pattern of hypometabolism in posterior regions, mainly in the cingulate cortex and in the medial aspects of parietal and occipital lobes. A more severe hypometabolism was observed in the right hemisphere of both patients. Both cases remitted with the use of specific immunotherapy for ANMDARE.

KEYWORDS: Cotard syndromenihilistic delusionsanti-NMDAR encephalitisautoimmune encephalitismolecular imaging

This paper proposes that ancestral use of irrigation increases autocracy and a culture of collectivism, & reduces contemporary female labor force participation and female property rights

Fredriksson, Per G.; Gupta, Satyendra Kumar (2020): Irrigation and Culture: Gender Roles and Women’s Rights, GLO Discussion Paper, No. 681, Global Labor Organization (GLO), Essen. https://www.econstor.eu/bitstream/10419/225005/1/GLO-DP-0681.pdf

Abstract: This paper proposes that ancestral use of irrigation reduces contemporary female labor force participation and female property rights. We test this hypothesis using an exogenous measure of irrigation and data from the Afrobarometer, cross-country data, the European Social Survey, the American Community Survey, and the India Demographic and Household Survey. Our hypothesis receives considerable empirical support. We find negative associations between ancestral irrigation and actual female labor force participation, and attitudes to such participation, in contemporary African and Indian populations, 2nd generation European immigrants, 1.5 and 2nd generation US immigrants, and in cross-country data. Moreover, ancestral irrigation is negatively associated with attitudes to female property rights in Africa and with measures of such rights across countries. Our estimates are robust to a host of control variables and alternative specifications. We propose multiple potential partial mechanisms. First, in pre-modern societies the men captured technologies complementary to irrigation, raising their relative productivity. Fertility increased. This caused lower female participation in agriculture and subsistence activities, and the women worked closer to home. Next, due to the common pool nature of irrigation water, historically irrigation has involved more frequent warfare. This raised the social status of men and restricted women’s movement. These two mechanisms have produced cultural preferences against female participation in the formal labor market. Finally, irrigation produced both autocracy and a culture of collectivism. These are both associated with weaker female property rights.

JEL Codes: J16, J21, N50, O10, P14, Q15, Z13.

Keywords: Irrigation; agriculture; culture; gender; norms; labor force participation; property rights.

5. Possible Mechanisms

In this section, we discuss possible mechanisms for the effect of irrigation potential on

female labor force participation and female property rights, respectively.

5.1. Female participation on pre-industrial agriculture

Boserup (1970) argues that males have historically captured technologies complementary

to irrigation, which increased their productivity in irrigated agriculture. Women worked with

less advanced technology and were relatively less productive. Irrigation activities may also be

dangerous (including to accompanying children), and may involve confrontations with

neighbors over water allocation. These factors all contribute to male labor specialization in

irrigated agriculture. While women still worked in agriculture to some degree, their work

gravitated toward the homestead, e.g. specializing in processing cereals and child care,

spending their lives mainly indoors or in the courtyard with little contact with non-relatives

(Ember, 1983).20

The Standard Cross-Cultural Sample (SCCS), compiled by Murdock and White (1969), has

data from 186 separate pre-industrial societies.21 The Ethnographic Atlas by Murdock (1967)

has data on 1,267 pre-industrial societies from around the world. The Atlas contains little

information about the societies themselves, however. The measure of the female-relative-tomale participation in overall agricultural production takes values from 1 to 5, where relative

participation is coded as follows. 1: males exclusively; 2: males predominantly; 3: equally; 4:

females predominantly; and 5: females exclusively. The dependent variables. The measure of

the relative time and effort spent on subsistence activities by females varies from 1 to 3, where

1: men expend more; 2: men and women expend roughly equal; 3: women expend more.

While the SCCS and the Atlas contain information on the centroid of each society, the

measurement of the precise location may involve errors. Moreover, information about the land

area covered by these pre-industrial societies is missing. We use a buffer zone of 200 km

around the centroid in order to construct the measure of irrigation potential and control

variables (Alesina et al., 2013). The ethnographic controls include suitability of the local

environment for agriculture, the presence of large domesticated animals, the proportion of the

local environment that is tropical or subtropical, an index of settlement density, and an index

of political development.

The mean variable values are provided in the table heading of Table 6. While column (1)

uses data from the Ethnographic Atlas, the remaining columns use SCCS data. Columns (1)-

(4) use female overall participation in agriculture as outcome variable, column (5) studies the

overall relative female contribution to subsistence in time and effort, and columns (6)-(8)

provide estimates for crop tending, harvesting, and milking, respectively. All columns include

fixed effects for the century-of-observance and language, ethnographic controls including plow

use, suitability of the local environment for agriculture, the presence of large domesticated

animals, the proportion of the local environment that is tropical or subtropical, economic

complexity, and political development.

Column (1) irrigation potential has a negative and statistically significant influence on

relative female participation in agricultural activities overall. The effect of moving from zero

to complete irrigation potential equals -1.45, which is substantial given the 3.04 mean. The

effect is stronger in column (2), using SCCS data. Column (3) adds a dummy for whether

cereals are the main crops, which Ember (1983) and Hansen et al. (2015) suggest influences

female labor force participation. The coefficient on irrigation potential rises further. Column

(4) controls for societies with formal class stratification systems, where males may be less

likely to participate in agricultural field work. The two added controls are insignificant, while

irrigation potential remains significant. Column (5) suggests that the female relative

contribution to subsistence activities were lower in societies with greater irrigation potential.

This reflects a shift away from agricultural field activities towards greater domestic and child

rearing duties. Columns (6)-(7) provide evidence that irrigation is associated with a decline in

female participation in some important agricultural activities outside the home, while column

(8) suggests the opposite effect occurred to milking which occurs closer to home. Table C5 in

online Appendix C provides cross-country OLS evidence that irrigation is associated with

restrictions on women’s freedom of movement within a country, using data from Coppedge et

al. (2019).

Overall, the results are consistent with women staying closer to the homestead in irrigated

areas during the pre-industrial time period. This suggests one possible partial mechanism which

links irrigation to lower contemporary female labor force participation rates and related

attitudes. The division of labor appears to have persisted through intergenerational cultural

transmission. [Table 6]

5.2. Warfare

Irrigation water is frequently a common pool resource. Since water consumption by

upstream communities may affect consumption by downstream communities, especially in

times of drought, conflicts are likely to occur. Anecdotal evidence includes Iraq and the

Andes.22 Irrigation agriculture also led to a storable surplus and relatively more valuable land,

providing incentives for raids and external warfare by other groups (e.g., Ember, 1982; Ang

and Gupta, 2018). We hypothesize that irrigation societies had a greater incidence of violent

external conflict. This yielded a greater demand for men due to greater muscle strength and

aggressiveness, improving their social standing (Chagnon, 1988; Ramos-Toro, 2019). RamosToro (2019) provides evidence of a negative relationship between exposure to conflict and

contemporary female labor force participation.23 Warfare may also have been associated with

reduced female mobility, and stricter social norms and restrictions on women’s labor market

participation outside the home.

Table 7 provides some support for this hypothesis. Columns (1)-(3) utilize society level

data from the SCCS (Murdock and White, 1969), while columns (4)-(9) use historical district

level data from India. The dependent variable in column (1) is a measure of external warfare.

We focus on societies with agricultural activities. We recode the Murdock and White (1969)

external warfare measure as follows: it takes a value of 1 if external war is ‘frequent, occurring

at least yearly’ or ‘common, at least every five years’; it takes a value of zero if ‘occasional, at

least every generation’ or ‘rare or never’. The sample size declines to 54. This renders language

and century fixed effects and the inclusion of tropical climate infeasible in this analysis. The

results should thus be interpreted with these drawbacks in mind. The logit model in column (1)

suggests that irrigation potential is positively associated with external warfare. Columns (2)-

(3) present ordered logit regressions. Column (2) is the basic model from Table 1 with female

participation in overall agriculture as the outcome variable (but with a smaller sample size).

External warfare is negative and significant in column (3), while the irrigation potential point

estimate declines modestly (in absolute value) from -2.00 to -1.67. This provides some support

for the hypothesis that a history of external warfare a partial channel between irrigation and

female participation in agriculture in pre-industrial societies.

Columns (4)-(9) provide district level evidence from India in support of the proposed

warfare mechanism. In rural India, most households working outside the home are engaged in

agricultural sector work (Kapsos et al., 2014). We measure female employment outside the

home by the ratio of the population of female agricultural workers to the total female population

in year 2011. In column (4), war count is a measure of the total number to land battles over

years 610-1962 occurring within a distance of 50km from the district, geocoded using Jacques

(2007).24 In column (7), the period of observations for war count is instead restricted to 1001-

1867AD. Jacques (2007) records relatively few instances of wars before 1001 (data quality

may be an issue), and in 1858 the British Crown took over the administration of India from the

British East India Company. The wars for accession of the native states ceased after 1857.

Columns (4) and (7) present negative binominal regressions, while columns (5), (6), (8), and

(9) are generalized linear model regressions. Geographical controls (temperature, precipitation,

latitude, area, land quality, and nightlight luminosity) and language fixed effects (largest

language group within the district, reflecting cultural variation across districts) are included.

One benefit of using data on India is the low interstate migration rate, which maintains longterm cultural differences (Kone et al., 2018).

Column (4) suggests a positive association between a district’s irrigation potential and the

historical experience with wars. When war count is included in column (6), the (absolute value

of the) irrigation potential point estimate declines relative to column (5), from -0.137 to -0.115,

while war count is negative and significant. The takeaway from columns (7)-(9) is similar.

These findings provide some support for the hypothesis that a history of warfare is a possible

partial mechanism linking irrigation and female participation in agriculture in contemporary

India. [Table 7]

5.3. Autocracy

Next, we provide evidence that historical irrigation may affect contemporary female

property rights regimes via an autocracy channel. Underpinned by resource curse theory,

Bentzen et al. (2017) argue that historical irrigation agriculture raised the likelihood that a preindustrial society was ruled by an elite based on the control of a natural resource. This has

yielded lower levels of contemporary democracy. Autocracies have weaker property rights

(Gradstein, 2007), and Fish (2002) suggests that authoritarianism is associated with negative

outcomes for women.25

To study the determination of female property rights, we utilize the standard general

measures of democracy, Polity2. The male political majority (in both democracies and

autocracies) is likely to determine the extent of female property rights. Table 8 shows that

democracy works as channel for the effect of irrigation potential on contemporary female

property rights. Column (1) establishes that irrigation potential has a negative effect on

democracy, measured by Polity2. In column (2), irrigation potential has a negative effect on

female property rights as shown above, but this effect disappears when we include democracy

in column (3). This suggests that the effect of irrigation on female property rights works at least

partially through the democracy channel. In contrast, while democracy has a positive

association with male property rights in column (5), there is no evidence that democracy works

as a link between irrigation and male property rights. [Table 8]

Table C6 in the online appendix provides additional evidence that attitudes, actual female

political participation rates, and the freedom to discuss politics are negatively associated with

irrigation potential. The first column uses a statement from the Afrobarometer as outcome

variable, and the remaining three columns use variables from Coppedge et al. (2019). 26

5.4. Individualism vs. Collectivism

This section investigates the cultural dimension of individualism vs. collectivism as a

possible potential mechanism. Buggle (2020) finds that irrigation is negatively correlated with

individualism, because irrigation required constant collaboration which yielded collectivism.

Gorodnichenko and Roland (2017) argue that the degree of individualism influences societies’

institutional choices. In particular, they find that individualism has a positive association with

the level of protection against expropriation risk, a measure of property rights. Binder (2019)

reports that collectivism is correlated with a belief in traditional gender roles.

Table 9 explores whether individualism vs. collectivism may function as a partial channel

between irrigation potential and contemporary female property rights. We use Hofstede et al.’s

(2010) measure of individualism and Coppedge et al.’s (2019) measure of property rights.

Irrigation potential has a negative correlation with individualism in column (1) and with female

property rights in column (2). This effect declines moderately (in absolute value) when

individualism is entered in column (3), from -1.75 to -1.64. However, a similar pattern occurs

for male property rights in columns (4) and (5), from -1.67 to -1.57. It appears that the

individualism vs. collectivism dimension of culture may provide a partial link between

irrigation potential and property rights for both genders. Thus, we do not find strong evidence

that this link is stronger for female than for male property rights. To investigate this further,

Table C7 in the online appendix includes both individualism and democracy as potential

mechanisms. It appears that both mechanisms work for female property rights, but only

democracy constitutes a channel for male property rights. [Table 9]

Taste is afforded the greatest relevance to nutrition as it is posited to have improved the probability of survival, helping screen safe and potentially toxic properties of foods; this teleology is dubious

Taste, teleology and macronutrient intake. Richard D Mattes. Current Opinion in Physiology, Volume 19, February 2021, Pages 162-167. https://doi.org/10.1016/j.cophys.2020.11.003

Abstract: Among the human sensory systems, taste is afforded the greatest relevance to nutrition as it is posited to have aided the identification and ingestion of nutrients in the environment and thereby improved the probability of survival. With respect to the macronutrients, sweet, umami and oleogustus (fat taste) reportedly facilitated meeting energy, essential amino acid and essential fatty acid requirements. However, such a teleological view fails to account for the fact that humans are largely blind to the primary sources of the macronutrients in the environment (starch, protein and triacylglycerol) and, in the case of protein and fat, the effective taste stimuli are generally unpleasant degradation products. Additional challenges to the prevailing teleology are also presented. Some have proposed that the sense of taste serves as a palatability screen that functions more basically by signaling safe and potentially toxic properties of potential foods. However, it is well documented that sensory qualities are unreliable predictors of food safety (sweet foods can be toxic and bitter foods nutritious). Instead, it is proposed that taste contributes to food choice by acquiring predictive information about wholesomeness through innate and learned mechanisms.

Sweet taste

Humans are limited to carbohydrates, fats and proteins as substrates to meet energy needs. Knowledge of the composition of ancient human diets is incomplete, but recent evidence supports a substantive contribution of starchy foods in many pre-agricultural populations [12] though it likely varied widely between subpopulations [13]. Access to simple carbohydrates would have been extremely low [14].

A functional role for sweet taste is forcefully made by reduced conservation of the sweet taste receptor and evidence of insensitivity to this quality by vertebrates not exploiting sweet foodstuffs (e.g. cats, sea lions, whales, pandas, horses, western clawed frog, vampire bats) as well as reemergence of sensitivity by hummingbirds who are exclusive nectar feeders while other birds lack this capability and food choice [15•,16,17••]. However, a broader analysis reveals a lack of association between losses of sweet taste sensitivity and diet [17••].

There are multiple additional observations that challenge the view that sensitivity to sweetness would be a functional mechanism to access carbohydrate. First, there is no essential mono or disaccharide and those are the predominant effective sweet taste stimuli. Thus, sweet taste is not tuned to an essential nutrient. Second, sources of sweet carbohydrate were extremely rare in the environment throughout most of human evolution. With the exception of limited access to honey and seasonal fruits, a receptor tuned to simple sugars would have served little purpose post-weaning. Even its role in promoting milk ingestion pre-weaning is uncertain. Fat is the primary determinant of the energy density of breast milk and studies with gruels varying in energy density and sweetness reveal intake is more closely related to energy density [18]. Also, interestingly, kittens who are carnivores and lack a functional sweet receptor nurse effectively [19] on mature cat milk that is approximately 4% lactose and only 6.3–8.6% protein [20]. Third, a more functional taste contribution to locating and promoting carbohydrate intake would have been sensitivity to starch which was abundant. There is preliminary evidence of human sensitivity to short chain oligosaccharides of 7 and 14 units (not 44) [21], but the sensation is not mediated by the T1R2–T1R3 (sweet) receptor and the sensation they evoke is not sweetness.

Further, it is clear that sweetness is an imperfect indicator of safe and available carbohydrate as sweet fruits are not necessarily rich sources of carbohydrate or energy (i.e. they have low energy density due to their high water content), not all sweet stimuli are carbohydrate (e.g. Monellin, Thaumatin, Brazzine are proteins) and some sweet molecules are toxic (e.g. lead acetate).

In summary, sweetness lacks the sensitivity and specificity to identify and promote the consumption of wholesome carbohydrates in the environment. However, it is not disputed that sweetness is rewarding and an appetitive signal that promotes feeding generally [18,22,23].

Umami taste

Proteins are comprised of amino acids, nine of which are considered essential that is, cannot be synthesized in humans so must be acquired from the diet. Rarely are free amino acids encountered in the environment because protein synthesis is extremely efficient. Amino acids are synthesized when needed to build proteins and in requisite proportions. Proteins play many roles in the body. They serve as enzymes, hormones, neurotransmitters, nutrient transporters, structural elements and are crucial for growth and development, pH balance, fluid balance, immune function and when consumed in excess of need, can provide energy.

Given these multiple essential roles, a teleological view would support a sensory system tuned to protein sources in the environment. However, the importance of taste in this regard is questionable. Some evidence suggests taste alone allows rapid identification of dietary protein sources in protein-depleted rats [24], but the preponderance of evidence indicates selection in rodents and other animals depends on post-ingestive learning where the sensory signal only acquires predictive power based on an association with a corrective post-ingestive outcome [25,26]. Second, a number of essential amino acids are effective taste stimuli, but a number of these elicit unpleasant sensations (e.g. methionine, leucine, tryptophan) and render protein hydrolysates unpalatable. This would discourage ingestion of the required nutrient.

The more specific case of Umami taste has attracted considerable attention. The prototypical stimulus for Umami taste is monosodium glutamate (MSG). Psychophysical studies in infants [27] and adults [28] indicate the stimulus is rejected when presented in water. In suprathreshold concentrations the quality of D-MSG is soapy-metalic and L-MSG is described as predominantly bitter [29], generally negative qualities. It is only in selected food contexts that it contributes a positive quality [30] and then this is augmented by the co-presence of 5′ ribonucoleotides [31]. Despite the low palatability of MSG, the teleological argument has been made that sensitivity to the compound signals the presence of protein sources in the environment and presumably the desirability of consuming them [32••]. Consistent with this view, herbivores generally lack the umami taste receptor [16]. However, the necessity of this signaling system is not supported. Selected animals have lost taste responsivity to umami (e.g. pig, horse, rabbit, tree shrew, mouse lemur, marmoset, tarsier, hyrax, sea lion, bottlenose dolphin) but all animals require protein [17••,33]. Additionally, if the teleological perspective that umami sensitivity aids acquisition of needed protein is true, individuals with low or marginal protein status should exhibit augmented hedonic responses to MSG containing foods. Heightened hedonic responses to other nutrients during periods of deficit have been documented [34]. While there is a report to this effect [35] for protein, the broader literature is not supportive [28,36]. Indeed, palatability is diminished in this state and is relatively heightened in the protein replete state [32••], counter to the hypothesis. An additional teleological argument holds that there would have been a survival benefit of detecting and consuming purine-rich foods which would contain higher concentrations of ribonucleotides. These foods can lead to elevated uric acid concentrations with consequent physiological responses that could have mitigated famine-related threats to survival [37]. If true, then, it is problematic now where famines are less common and diseases of overconsumption predominate, including gout, hypertension and glucose intolerance. If gustatory wisdom held in this case, it appears to have been lost or rendered non-functional in the current environment.

Taken together, the evidence indicates food choices related to satisfying protein requirements are guided more by non-protein specific signals that become associated with post-ingestive cues that protein needs are met and umami taste, in particular, serves to promote the overall palatability of the diet and thereby encourages food intake generally [38].

Fat taste (Oleogustus)

Linoleic acid and alpha-linolenic acid (ALA) are essential fatty acids (EFA) for humans, that is, they cannot be synthesized in the body and must be obtained via the diet. Eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) can be synthesized from ALA, but the conversion efficiency is low so a dietary source is beneficial. These fatty acids serve multiple purposes in the body. They have anti-inflammatory activity, are structural elements in cell membranes and are precursors to a range of bioactive compounds. Additionally, fats, in general, are the most energy dense macronutrient. Thus, a system to detect them and promote their consumption would hold survival value.

Though there have been isolated claims that there is a taste for fat, this view received little empirical support until recently [39••]. The predominant signals from dietary fat were considered visual, somatosensory and olfactory. The somatosensory contribution from triacylglycerols, the predominant form of dietary fat, include sensations such as creaminess, viscosity, lubricity, and mouth-coating and are largely rated as appetitive (i.e. palatable). In contrast, the olfactory cues, stemming primarily from free fatty acids (FFA) derived from triacylglycerol, are largely considered aversive. Consequently, for most foods, concentrations of free fatty acids are purposefully held below detection thresholds during product development. Of course, through experience even strong fat-based odors can acquire a positive valence. Work demonstrating dietary fat can elicit an early spike in plasma triacylglycerol concentrations when somatosensory and olfactory cues were largely controlled, suggested a role for taste [40]. Studies in mice indicate FFA, not triacylglycerol, are the effective taste stimuli [41]. Subsequent studies documented measurable and differential taste threshold for various fatty acids [42] in humans and the qualities appear to change with fatty acid chain length. Short-chain fatty acids are largely sour (<C:6) while longer chain fatty acids (>C:16) evoke an unpleasant sensation that is unique from other primary taste qualities [43] and has been termed oleogustus. The essential fatty acids are consistently rated as unpleasant. They would be encountered in the environment largely through rancid foods and it has been posited that they act more as warning signals than appetitive signals. This is inconsistent with a teleological perspective that the function of oleogustus is to aid in the acquisition of EFA and/or energy. Indeed, it has further been proposed that high fat intake occurs because of insensitivity to the taste of fatty acids [44]. There is the possibility that the taste of low concentrations of long-chain FFA could contribute positively to the overall flavor profile of some foods, just as bitter notes, unpleasant in isolation, contribute to the palatability of selected foods (e.g. wines, chocolate, coffee). Of course, if one accepts this caveat, it is also true that bitterness cannot be regarded as a uniformly aversive signal protecting against toxin exposure.

Whether oleogustus qualifies as a taste primary is not settled science. If it is accepted, the effective taste stimulus would most likely occur in rancid foodstuffs. The quality of the sensation would discourage ingestion and hinder meeting EFA and energy needs.