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The Intensity of Human Body Odors and the MHC: Should We Expect a Link?

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Evolutionary Psychology 4(1)

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It is now well established that genes within the m ajor histocompatibility complex (MHC) somehow affect the production of body odors in several vertebrates, including humans. Here we discuss whether variation in the intensity of body odors may be influenced by the MHC. In order to examine this question, we have to control for MHC-linked odor perception on the smeller's side. Such a control is necessary because the perception of pleasantness and intensity seem to be confounded, and the causalities are still unsolved. It has previously been found that intense odors are scored as less pleasant if the signaler and the receiver are of MHC-dissimilar type, but not if they are of MHC similar type. We argue, and first data suggest, that an effect of the degree of MHC-heterozygosity and odor intensity is likely (MHC-homozygotes may normally smell more intense), while there is currently no strong argument for other possible links between the MHC and body odor intensity.

The average odor intensity of T-shirts worn by men who are either heterozygous on all the MHC loci analysed, or who are homozygous on at least one of these loci. The figure gives the mean (+SE) scorings of MHC similar (open bars) and MHC-dissimilar smellers (closed bars) for the same 38 odors each. The p-values are two-tailed.

…

: Tests for possible MHC effects on the intensity of male body odors. MHC- linked perception is controlled for by using weighted mean scorings of MHC-similar and MHC-dissimilar smellers.

…

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Evolutionary Psychology

human-nature.com/ep – 2006. 4: 85-94

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Original Article

The Intensity of Human Body Odors and the MHC: Should We Expect A

Link?

Claus Wedekind, Department of Ecology and Evolution, Biophore, University of Lausanne, 1015

Lausanne, Switzerland; Program for Evolutionary Dynamics, and Department of Organismic and

Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; Zoological Institute,

University of Bern, 3032 Hinterkappelen, Switzerland. Email: claus.wedekind@unil.ch.

Thomas Seebeck, Institute of Cell Biology, Uni

ersity of Bern, 3012 Bern, Switzerland.

Florence Bettens, Institute of Immunology, University Hos

ital Bern, 3010 Bern, Switzerland.

Alexander J. Paepke, Zoological Institute, University o

Bern, 3032 Hinterkappelen, Switzerland.

Abstract: It is now well established that genes within the m

ajor histocompatibility

complex (MHC) somehow affect the production of body odors in several vertebrates,

including humans. Here we discuss whether variation in the intensity of body odors

may be influenced by the MHC. In order to examine this question, we have to control

for MHC-linked odor perception on the smeller’s side. Such a control is necessary

because the perception of pleasantness and intensity seem to be confounded, and the

causalities are still unsolved. It has previously been found that intense odors are

scored as less pleasant if the signaler and the receiver are of MHC-dissimilar type, but

not if they are of MHC similar type. We argue, and first data suggest, that an effect of

the degree of MHC-heterozygosity and odor intensity is likely (MHC-homozygotes

may normally smell more intense), while there is currently no strong argument for

other possible links between the MHC and body odor intensity.

Keywords: Odor intensity, MHC homo- and heterozygosity, 'good genes'

hypothesis,

'compatible genes' hypothesis, T-shirt experiment.

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Introduction

The physiology and the biological significance of human body odors is

multifaceted and not yet well understood yet (Beauchamp and Yamazaki, 2005;

Grammer et al., 2005; McClintock et al., 2005; Yamazaki and Beauchamp, 2005;

Ziegler et al., 2005). The reason for this lack of knowledge seems obvious: odors are

often short-lived and difficult to store, hard to describe, and still very difficult to

analyse chemically, at least in the quantities that can be relevant in social contexts.

The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

Despite these analytical problems and the shortage of hard data, humans seem to vary

in the intensity of their odors, even if we correct for behavioral and environmental

factors. Among humans, there is variation in the size and the number of glands on the

skin (Stoddart, 1990), variation in gland activity (Kreyden et al., 2002), and obvious

variation in the number and density of those body hairs that amplify odors through

their support of microorganisms and their role in odor diffusion. However, our

personal perception can easily mislead us when it comes to the generality of odor

quality and intensity.

Whether or not an odor is perceived as intense depends not only on the kind

and the amount of volatile molecules that are emitted (the strength of the signal), but

also on factors that influence the perception of the odor (the sensitivity of the

receiver). With regard to the latter, there are many factors that may play a role. For

example, it seems that women are usually more sensitive to body odors than men

(Dalton et al., 2002), and that the sensitivity for odor components can be trained in

women during their reproductive age (Dalton et al., 2002). Also, the perception of

body odors varies within the menstrual cycle (Doty et al., 1981; Gangestad and

Thornhill, 1998; Rikowski and Grammer, 1999), changes with pregnancy (Gilbert

and Wysocki, 1991), generally decreases with age (Wedekind and Füri, 1997) and

appears to be influenced by the contraceptive pill (Wedekind et al., 1995; Thorne et

al., 2002).

The perception of body odors is also linked to genes of the MHC (Yamazaki

et al., 1976; Penn and Potts, 1999; Ziegler et al., 2005). These genes can be quite

important in explaining odor preferences. In T-shirt experiments, when the influence

of many potentially confounding variables is reduced, up to 23 % of the variance in

pleasantness could be explained by the degree of similarity at the loci of the MHC

between T-shirt wearer and smeller (Wedekind & Füri 1997). In mice, the estimates

are even higher and reach up to 50% (Ziegler et al., 2005). The intensity of one and

the same body odor can be perceived very differently by different individuals. In

Wedekind & Füri (1997), when 121 students rated the same six odors for intensity,

pleasantness and sexiness, all the odors received nearly all possible scores from very

weak to very intense. In one case (Wedekind et al. 1995), a women even reported

nausea for several hours after smelling the experimental T-shirts. She specifically

linked her nausea to one odor which she rated as very intense and very unpleasant,

while other smellers scored this particular odor as less intense and quite pleasant. In

this context, it may be interesting that this woman was using the contraceptive pill at

the time of the experiment. Pregnancy, which is partly simulated by the pill, is often

linked to nausea and vomiting as a response to odors (Heinrichs, 2002).

Wedekind et al. (1995) found that the perception of pleasantness and of

intensity of an odor are correlated if smeller and odor source have dissimilar MHC

types, but not if they are of similar MHC type. Since non-related individuals are

normally dissimilar at the MHC , we would expect that, as a general tendency,

weaker body odors are normally rated as more pleasant than more intense ones. This

expectation was confirmed by Wedekind & Füri (1997). However, the causality

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

remains unclear. Is an odor perceived as unpleasant because it is intense, or as intense

because it is unpleasant?

Not controlling for MHC-linked odor perception can introduce disturbing

biases in an analysis of odor intensity. Vice versa, a lack of control for odor intensity

can confound or weaken an analysis of MHC-dependent preferences (Wedekind and

Seebeck, 1996; Wedekind, 2002; Roberts et al., 2005). It is therefore necessary to

disentangle possible MHC effects on odor intensity from MHC-dependent odor

perception. In a previous study we used an experimental method that allows to test

for, and to control for, MHC-dependent variation in odor perception within a

population (Wedekind et al., 1995). Here we use the data of Wedekind et al. (1995)

to analyse, on the one hand, intensity ratings of receivers that are either dissimilar or

similar to the signaller’s MHC, i.e. we control for the effects of the MHC by

analysing possible effects within the two experimental groups. On the other hand, we

calculate MHC-neutral odor scores that can be used as estimates of the average

intensity of body odors. We use these neutral scores to ask whether the intensity of a

man’s odor is in any way connected to his MHC genotype. We test three questions: 1)

Is the degree of MHC heterozygosity linked to odor intensity? 2) Are the odors of

carriers of most common MHC antigens generally perceived as differently intense

than other body odors? 3) Are men with more intense odors also more similar to each

other in their MHC genotypes than expected by chance? Effect size approximations

are used to quantify the observed trends in the data and to estimate the significance of

each possible link between MHC and odors intensity. We use our analyses to discuss

several hypotheses on the biology of MHC-linked odor signalling in humans.

Methods

The 38 men whose odors are studied here were on average 24.5 years old (SD

= 2.2) and students of the University of Bern at the time of the experiments. They all

appeared to be of Caucasian origin, spoke the Swiss German dialect without any

obvious accents, and had forenames and surnames that are common in the German

speaking part of Switzerland. They were typed for their MHC (HLA-A, -B, and –DR)

and asked to wear T-shirts during two nights. The odors of these worn T-shirts were

subsequently evaluated by women who had an MHC type that was either similar (on

average 2.7 dissimilar antigens) or dissimilar (on average 5.9 dissimilar antigens) to

the T-shirt wearer’s MHC. See Wedekind et al. (1995) for a detailed description of

the methods and for an analysis of the general effects of the MHC on these odors and

on female preferences for them.

We use three procedures to control for MHC-linked odor preferences. First,

there is evidence for an interaction between MHC-linked preferences and the

contraceptive pill (Wedekind et al., 1995). Since the exact nature of this interaction is

not fully understood yet, we only used evaluations of women who did not use the

contraceptive pill during the time of the experiments (we could therefore only use a

subset of the data of Wedekind et al. (1995) in the present analyses). Second, each

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

odor was evaluated by on average 4.7 women (range 2 to 12) and at least once each

by a woman with similar or dissimilar MHC type, respectively. We tested for possible

links between odor intensity and the MHC within each to the two experimental

groups (“similar” and “dissimilar”). Third, we averaged the ratings of all MHC-

similar and MHC-dissimilar women and used the mean of these two average ratings

to obtain scores that includes the ratings of many women but are neutral with respect

to the degree of MHC similarity between the man and the smelling women.

We used parametric test statistics when graphical inspections of the data

suggested that the respective model assumptions were met. In order to test whether

the men’s MHC type is correlated to the intensity of their body odors, we used the

following test procedures: (i) We tested whether the degree of MHC heterozygosity is

linked to odor intensity in two-sample t-tests; (ii) we used again two-sample t-tests to

test whether the presence or absence of the most common MHC antigens in the study

population was linked to the average odor intensity; (iii) we grouped the men into two

groups of N=19 each according to their odor intensity (“strong” versus “weak”). We

then tested whether these two groups also clustered with respect to the average degree

of similarity on the MHC. This was done by comparing the mean number of

dissimilar antigens of all pairwise comparisons within each group to a null

expectancy. This null expectancy was derived from 1000 random permutations of the

above procedure (randomization test). Power analyses for two-sample t-tests were

done online on www.stat.uiowa.edu/~rlenth/Power/, assuming equal variances and

equal sample sizes.

Results

Of the 38 men tested, 17 (45%) were typed as homozygous for at least one

MHC antigen. On average, their odors were not significantly more intense than those

of MHC heterozygotes (Table 1). The estimated effect size (in average standard

deviations) was d = 0.552. A power analysis revealed that if we missed an existing

effect (type II error), one would have an 80% change of finding it at p = 0.05 if the

sample size were about tripled (Table 1). However, three men were homozygous for

two of the three loci, and their average body odor intensity was even slightly lower

than the intensity of the other homozygotes.

Since we have two average scorings for each odor, one by MHC-similar and

one by MHC-dissimilar smeller, we could also test for the effect of the signallers’

MHC homozygosity within each group of smellers. We found that the intensity scores

of MHC-similar smellers were not significantly influenced by homozygosities on the

signaller’s side, while MHC homozygotes smelled significantly more intense to

MHC-dissimilar smellers than MHC heterozygotes (Figure 1). These intensity scores

did not seem to be significantly influenced by the perception of pleasantness (within

each experimental group,|t| always < 0.82, p always > 0.42). However, when all mean

scores per signaller were correlated, pleasant odors tended to be less intense ones

(Spearman rank order correlation coefficient r

= -0.46, p = 0.003).

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

Figure 1: The average odor intensity of T-shirts worn by men who are either

heterozygous on all the MHC loci analysed, or who are homozygous on at least one

of these loci. The figure gives the mean (+SE) scorings of MHC similar (open bars)

and MHC-dissimilar smellers (closed bars) for the same 38 odors each. The p-values

are two-tailed.

MHC-dissimilar

smellers

p = 0.02

MHC-similar

smellers

p = 0.77

Odor intensity

No Yes No Yes

Homozygous on MHC loci

The most common MHC antigen in the population is by far HLA-A2, with a

prevalence of 50% in the present sample, and around 50% in comparable samples

(Grundschober et al. 1994, Wedekind & Füri 1997, Milinski and Wedekind 2001).

We found no significant effect of this antigen (Table 1) or any of the eight other most

common antigens that Milinski & Wedekind (2001) listed (|t| always < 1.33, p always

> 0.19). The group of homozygotes were not dominated by men who possessed HLA-

A2 (only 37% of them are homozygous on any MHC locus, χ

= 0.47, p = 0.49).

Therefore, the second analysis in Table 1 is not confounded with the first. The

estimated effect size for HLA-A2 as grouping factor was d = 0.339. We found

analogous non-significant results if we tested for a possible effect of HLA-A2 within

the scorings of the MHC-similar and MHC-dissimilar smellers, respectively (|t|

always < 0.8, p always > 0.42).

Men with more intense odors do not have significantly more similarities in

their MHC genotypes than expected by chance (Table 1). The one-tailed

randomization tests did not reveal any tendencies. It turned out that exactly half of all

men with HLA-A2 were each in the group “intense” and the group “weak” (χ

= 0.0,

p = 1.0). Hence, the results of the third test in Table 1 can be seen as statistically

independent of the second test.

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

Table 1: Tests for possible MHC effects on the intensity of male body odors. MHC-

linked perception is controlled for by using weighted mean scorings of MHC-similar

and MHC-dissimilar smellers.

Question

Analysis*

Test**

min

***

Conclusion if

tendency indicated

real effect

(i) Effect of MHC-

homozygosity?

(17 of 38 men are

homozygote)

= 5.21 (1.87)

= 6.17 (1.59)

t = 1.67

= 0.10

106

MHC homozygotes

would smell more

intense than others.

(ii) Effects of most

common MHC antigen?

(18 of 38 men have

HLA-A2)

= 5.35 (1.82)

= 5.96 (1.76)

t = 1.04

= 0.30

276

Men with the most

common MHC antigen

would smell more

intense than others.

(iii) Average similarities

in MHC-types

- among 19 men with

relatively intense odors?

- among 19 men with

relatively weak odors?

Randomization test

obs

= 4.62, µ

exp

= 4.61

obs

= 4.78, µ

exp

= 4.61

= 0.51

= 0.97

No tendency towards

any clustering of MHC-

type with odor intensity

* Mean (SD)

** P

= two-tailed, P

= one-tailed

*** The number of male odors that would be needed to demonstrate an effect (if it exists) at α = 0.05

with a probability of 80%.

Discussion

MHC-linked odor and mate preferences are typically seen as today’s best

example of sexual selection for compatible genes, i.e. for a choice of genetic

complementarity (reviews in Mays and Hill, 2004; Neff and Pitcher, 2005). In such

compatible-genes sexual selection models, the intensity of a signal is not necessarily

expected to be linked to its information content (Trivers, 1972; Wedekind, 1994;

Tregenza and Wedell, 2000). Alternatively, the so called “good-genes” models of

sexual selection (Zahavi, 1975; Grafen, 1990; Møller and Alatalo, 1999) predict a

correlation between signal intensity and health and vigor. The argument here is that

health and vigor is expected to depend on overall genetic quality, and only

individuals in good health and vigor can afford the costs of the signal.

We may often assume that the intensity of a signal is positively correlated

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

with health and vigor, because stronger signals are normally more expensive to

produce or maintain. In the case of body odors, however, it is not immediately clear

whether an odor that is perceived as intense (i) is an indicator of better overall health

and vigor (Zahavi, 1975), or (ii) is perceived as intense because intensity rating is

confounded with pleasantness rating, and unpleasant odors tend to be rated as intense

regardless of the amount of volatiles that are involved. In the second case, high-

quality odor components, i.e. components that are more expensive to the signaller and

more attractive to the perceiver, may cause an odor to be rated as more pleasant and

hence less intense. At the moment, we have to leave it open which scenario is more

likely for human body odors. Nevertheless, the two types of sexual selection models

mentioned above still make clear predictions for the case of body odors. If MHC-

linked sexual selection is indeed about finding genetically compatible mates, we

would not expect a link between odor intensity and the specificity of MHC antigens.

If, however, some MHC-antigens or antigen-combinations are better adapted to

current challenges than others, body odors pleasantness and/or intensities may be

correlated to the MHC because they reveal an individual’s health and vigor (as seems

to be the case for spurs in pheasants (von Schantz et al., 1996)). As one possibility,

we may then predict a link between odor intensity and the specificity of MHC

antigens. Our effect-size estimations and the power analyses suggest that such a link

does not exist or is very weak in the case of human body odors. This observation for

itself contradicts the good-genes sexual selection hypothesis and is in agreement with

the compatible-genes sexual selection hypothesis (Neff & Pitcher 2005).

Brown (1997) suggested that the overall degree of heterozygosity or the

degree of heterozygosity on certain key loci may be positively linked with an

individual’s health and vigor, and that sexual signals may therefore reveal

heterozygosity at these loci. In the case of the MHC, it seems that these loci are still

under selection in many human populations, because MHC heterozygotes are

normally more frequent than expected under Hardy-Weinberg equilibrium (Hedrick

and Thomson, 1983; Black and Hedrick, 1997). However, it is not entirely clear

whether this is due to natural or sexual selection, or both (Apanius et al., 1997;

Prugnolle et al., 2005). If natural selection is responsible for these findings, MHC

heterozygotes are generally in better health and vigor than people with homozygous

MHC loci. Brown’s (1997) hypothesis would then predict a link between MHC

heterozygosity and characteristics that are used for mate selection. Indeed, Robert et

al. (2005) recently found a link between MHC heterozygosity and facial

attractiveness in humans. In their experiments, MHC heterozygosities were scored as

more attractive, and when the scores were specifically asked for, faces of MHC

heterozygous subjects were perceived as “healthier” than faces of people with

homozygosities at the MHC locus.

In the case of body odors the direction of a possible correlation between MHC

heterozygosity and signal intensity is not immediately obvious. Our first results and

the effect size estimates suggest that there could be a difference in odor intensity

between MHC heterozygotes and homozygotes, with homozygotes smelling more

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The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

intensely, especially for MHC-dissimilar smellers (i.e. for most individuals in an

outbred and MHC-diverse population). However, we do not know whether MHC

heterozygosity and health and vigor are correlated in our study population.

Alternatively to Brown’s (1997) hypothesis, it is possible that there is no link

between MHC heterozygosity and the signaller’s health and vigor, and that the

differences between MHC homozygotes and heterozygotes are explained by some yet

unknown constraints in the physiology of odor production.

In conclusion, if we control for MHC-linked perception we find few

indications for a possible link between body odor intensity and MHC specificity. It

appears that MHC homozygotes produce body odors that are on average perceived as

more intense than those of heterozygotes. If such a link can be verified in future

studies, it may indicate a statistical link between MHC homozygosity and general

health and vigor or, alternatively, it may contribute to a better understanding of the

physiology of MHC-linked odor production.

Acknowledgements

We thank the participants for making this study possible, E. Frei, S. Füri, K.

Viragh, B. Streb and M. Perlen for technical assistance, and C. Dulac, S. Edwards, M.

Walker, and an anonymous reviewer for discussion and/or helpful comments on the

manuscript. The study was supported by the Roche Foundation, the Swiss National

Science Foundation, and a Sarah and Daniel Hrdy Visiting Fellowship to CW.

Received 20 September, 2005; Revision received 22 March, 2006; Accepted 22

March, 2006.

References

Apanius, V., Penn, D., Slev, P. R., Ruff, L. R. and Potts, W. K. (1997). The nature of

selection on the major histocompatibility complex. Critical Reviews in

Immunology, 17: 179-224.

Beauchamp, G. K. and Yamazaki, K. (2005). Individual differences and the chemical

senses. Chemical Senses, 30: I6-I9.

Black, F. L. and Hedrick, P. W. (1997). Strong balancing selection at HLA loci:

Evidence from segregation in South Amerindian families. Proceedings of the

National Academy of Sciences USA, 94: 12452-12456.

Brown, J. L. (1997). A theory of mate choice based on heterozygosity. Behavioral

Ecology, 8: 60-65.

Dalton, P., Doolittle, N. and Breslin, P. A. S. (2002). Gender-specific induction of

enhanced sensitivity to odors. Nature Neuroscience, 5: 199-200.

Doty, R. L., Snyder, P. J., Huggins, G. R. and Lowry, L. D. (1981). Endocrine,

cardiovascular, and psychological correlates of olfactory sensitivity changes

Evolutionary Psychology – ISSN 1474-7049 – Volume 4. 2006.

- 92 -

The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

during the human menstrual cycle. Journal of Comparative Physiology and

Psychology, 95: 45-60.

Gangestad, S. W. and Thornhill, R. (1998). Menstrual cycle variation in women's

preference for the scent of symmetrical men. Proceedings of the Royal Society

of London Series B, 265: 927-933.

Gilbert, A. N. and Wysocki, C. J. (1991). Quantitative assessment of olfactory

experience during pregnancy. Psychosomatic Medicine, 53: 693-700.

Grafen, A. (1990). Biological signals as handicaps. Journal of Theoretical Biology,

144: 517-546.

Grammer, K., Fink, B. and Neave, N. (2005). Human pheromones and sexual

attraction. European Journal of Obstetrics Gynecology and Reproductive

Biology, 118: 135-142.

Grundschober, C., Sanchez-Mazas, A., Excoffier, L., Langaney, A., Jeannet, M.,

Tiercy, J. M. (1994) HLA-DPB1 DNA polymorphism in the Swiss

population: linkage disequilibrium with other HLA loci and population

genetic affinities. European Journal of Immunogenetics, 21: 143-157.

Hedrick, P. W. and Thomson, G. (1983). Evidence for balancing selection at HLA.

Genetics, 104: 449-456.

Heinrichs, L. (2002). Linking olfaction with nausea and vomiting of pregnancy,

recurrent abortion, hyperemesis gravidarum, and migraine headache.

American Journal of Obstetrics and Gynecology, 186: S215-S219.

Kreyden, O. P., Böni, R. and Burg, G. (eds.). (2002). Hyperhidrosis and botulinum

toxin in dermatology . Karger, Basel.

Mays, H. L. and Hill, G. E. (2004). Choosing mates: good genes versus genes that are

a good fit. Trends in Ecology & Evolution, 19: 554-559.

McClintock, M. K., Bullivant, S., Jacob, S., Spencer, N., Zelano, B. and Ober, C.

(2005). Human body scents: Conscious perceptions and biological effects.

Chemical Senses, 30: I135-i137.

Milinski, M. and Wedekind, C. (2001). Evidence for MHC-correlated perfume

preferences in humans. Behavioral Ecology, 12: 140-149.

Møller, A. P. and Alatalo, R. V. (1999). Good-genes effects in sexual selection.

Proceedings of the Royal Society of London Series B-Biological Sciences,

266: 85-91.

Neff, B. D. and Pitcher, T. E. (2005). Genetic quality and sexual selection: an

integrated framework for good genes and compatible genes. Molecular

Ecology, 14: 19-38.

Penn, D. J. and Potts, W. K. (1999). The evolution of mating preferences and major

histocompatibility complex genes. American Naturalist, 153: 145-164.

Prugnolle, F., Manica, A., Charpentier, M., Guegan, J. F., Guernier, V. and Balloux,

F. (2005). Pathogen-driven selection and worldwide HLA class I diversity.

Current Biology, 15: 1022-1027.

Rikowski, A. and Grammer, K. (1999). Human body odour, symmetry and

attractiveness. Proceedings of the Royal Society of London Series B, 266: 869-

Evolutionary Psychology – ISSN 1474-7049 – Volume 4. 2006.

- 93 -

The Intensity of Human Body Odors and the MHC: Should We Expect A Link?

Evolutionary Psychology – ISSN 1474-7049 – Volume 4. 2006.

- 94 -

874.

Roberts, S. C., Little, A. C., Gosling, L. M., Perrett, D. I.,

Carter, V., Jones, B. C.,

Penton-Voak, I. and Petrie, M. (2005). MHC-heterozygosity and human facial

attractiveness. Evolution and Human Behavior, 26: 213-226.

Stoddart, D. M. (1990). The scented ape. The biology and culture of human odour.

Cam

bridge University Press.

Thorne, F., Neave, N., Scholey, A., Moss, M. and Fink, B. (2002). Effects of putative

le pheromones on female ratings of male attractiveness: Influence of oral

contraceptives and the menstrual cycle. Neuroendocrinology Letters, 23: 291-

297.

Tregenza, T. and Wedell, N. (2000). Genetic compatibility, ma

te choice and patterns

of parentage: Invited review. Molecular Ecology, 9: 1013-1027.

Trivers, R. L. (1972). Parental investment and sexual selection. - In: Campbell, B.

(ed.) Sexual selection and the descent of m

an. Aldine Press, pp. 136-179.

von Schantz, T., Wittzell, H., Goransson, G., Grahn, M. and Persson, K. (1996).

MHC genotype and m

ale ornamentation: Genetic evidence for the Hamilton-

Zuk model. Proceedings of the Royal Society of London Series B, 263: 265-

271.

Wedekind, C. (1994). Handicaps not obligatory in sexual selection for resistance

genes. Journal of Theoretical Biology, 170: 57-62.

Wedekind, C. (2002). The MHC and body odors: arbitrary effects caused by shifts of

mean pleasantness.

Nature Genetics, 31: 237-237.

Wedekind, C. and Füri, S. (1997). Body odour preferences in men and wom

en: do

they aim for specific MHC combinations or simply heterozygosity?

Proceedings of the Royal Society of London Series B, 264: 1471-1479.

Wedekind, C. and Seebeck, T. (1996). MHC and ma

te selection in humans? Reply.

Trends in Ecology & Evolution, 11: 24-25.

Wedekind, C., Seebeck, T., Bettens, F. and Paepke, A. J. (1995). MHC-dependent

mate preferences in humans. Proceedings of the Royal Society of London

Series B, 260: 245-249.

Yamazaki, K. and Beauchamp, G. K. (2005). Chemosensory recognition of olfactory

individuality. Chemical Senses, 30: I142-i143.

Yamazaki, K., Boyse, E. A., Mike, V., Thaler, H. T., Mathieson, B. J., Abbott, J.,

Boyse, J., Zayas, Z. A. and Thomas

, L. (1976). Control of mating preference

in mice by genes in the major histocompatibility complex. Journal of

Experimental Medicine, 144: 1324-1335.

Zahavi, A. (1975). Mate selection - a selection for a handicap. Journal of theoretical

Biology, 53: 205-214.

Ziegler, A., Kentenich, H. and Uchanska-Ziegler, B. (2005). Fema

le choice and the

MHC. Trends in Immunology, 26: 496-502.

Swarm Robot dalam Pencarian Sumber Asap

Book

Full-text available

Jan 2010

”Swarm Robot dalam Pencarian Sumber Asap”. Buku yang dibuat berdasarkan hasil penelitian sejak tahun 2000 ini mengusung tema metoda pencarian sumber asap dengan menggunakan robot otonom. Topik pencarian sumber asap merupakan penelitian yang masuk dalam bidang robotika dan kecerdasan buatan. Pada bagian awal buku, kami menyajikan pengertian dasar mengenai gas dan asap serta beberapa fungsinya dalam kehidupan sehari-hari. Disini pembaca diajak untuk melihat mengenai bahaya dan kebutuhan dari penelitian yang kami lakukan. Ketika bicara gas dan asap, maka mau tidak mau bau juga akan termasuk didalamnya. Bau juga memiliki banyak fungsi, baik dalam kesehatan, kenyamanan, maupun kebersihan. Pada pencarian sumber asap secara manual, bau merupakan indikator yang sangat bermanfaat karena dapat membantu pencari menentukan seberapa jauh dan posisi tepat sumber bau. Selain bau, penguraian zat di udara secara kimia dapat juga dimanfaatkan untuk pencarian. Teknik kedua inilah yang kami gunakan dalam penelitian. Pada buku ini juga dijelaskan tentang perkembangan metode pencarian, mulai dari pencarian yang menggunakan satu agen sampai yang menggunakan banyak agen. Pada bagian menjelang akhir, kami menyajikan modiﬁkasi yang telah dilakukan untuk meningkatkan kualitas algoritma pencarian. Seluruh modiﬁkasi dapat dicoba dalam perangkat lunak robot pencari sumber asap yang juga dibuat oleh tim peneliti. Tak hanya metode pencarian, desain robot yang merupakan salah satu elemen penting pada pencarian sumber asap juga dijabarkan secara komperhensif.

Molecular Imprinted Polymers for Sensing of Volatile Organic Compounds in Human Body Odor

Chapter

Full-text available

Nov 2016

Sunil Jha

Physical Cues of Partner Quality

Chapter

Feb 2023

The dominant evolutionary theory of sexual attraction posits that attraction serves as a psychobehavioral and motivational mechanism for identifying healthy, fertile, and appropriate mates. According to this theory, humans and animals display cues that reflect their mate quality and, if successful, are perceived as attractive by potential mates. There is evidence for such valid cues in human faces, bodies, and non-bodily traits, which include adornments and items that signal provisioning ability, creativity, artistic skills, or conspicuous consumption. In this chapter, we discuss the evidence for the existence of these facial, bodily, and non-bodily cues and for their role in communicating aspects of partner quality, including health, fertility, developmental stability, genetic quality, and potential for parental investment. We further discuss sex differences in the physical cues that men and women rely on in mate choice. We conclude by highlighting the centrality and evolutionary importance of physical cues in contemporary sexual selection, and how they manifest in evolutionarily novel inventions such as physical self-enhancements, “sexy selfies,” social media, and online dating.

Physical cues of partner quality

Chapter

Full-text available

Feb 2021

The dominant evolutionary theory of sexual attraction posits that attraction serves as a psychological mechanism for identifying healthy, fertile, and appropriate mates. According to this theory, humans and animals display cues that reflect their mate quality and are perceived as attractive by potential mates. There is evidence for such valid cues in human faces, bodies, and in non-bodily traits, which include adornments and items that signal provisioning ability, creativity, artistic skills, or conspicuous consumption. In this chapter, we discuss the evidence for the existence of these facial, bodily, and non-bodily cues, and for their role in communicating aspects of partner quality, including health, fertility, developmental stability, genetic quality, and potential for parental investment. We further discuss sex differences in the kinds of physical cues that men and women rely on in mate choice. We conclude by noting how central and evolutionarily important physical cues are even in contemporary sexual selection, and how the importance of physical cues of partner quality manifests in evolutionarily novel inventions such as physical self-enhancements, social media, and online dating.

Characterization of human body odor and identification of aldehydes using chemical sensor

Article

Full-text available

Dec 2016
REV ANAL CHEM

Sunil Jha

Human body odor is a unique identity feature of individual as well as an established composite of numerous volatile organic compounds (VOCs) belonging to significant chemical classes. Several analytical methods have been used in the characterization of human body odor in order to recognize the chemical composition of VOCs in medical, forensic, and biometric applications. Besides, real-time sensing systems (based on the chemical sensors) are being researched and developed for qualitative and quantitative recognition of VOCs in body odor. The present review focuses the state-of-the-art research outcomes related to the characterization of human body odor with the objective to identify the VOCs belonging to aldehyde class. Furthermore, the application of chemical sensors in past studies for the detection of aldehydes besides other chemical compounds in body odor is summarized and the significance of aldehydes detection in different applications is discussed.

Chemical Fingerprinting of Human Body Odor: An Overview of Previous Studies

Article

Full-text available

Apr 2014

Analysis of human skin emanations has been growing of the past few years, so that it can be utilized more effectively in the cosmetic field, canine training and criminal investigation. The volatile organic compounds (VOC) present in the head space of human body odor, either by presence or by difference in abundance, leads to the uniqueness of each individual. A few theories regarding the production of human scent and its characteristics have also been explored in this paper. Human scent can be categorized into three components namely primary odor, secondary odor and tertiary odor, where primary odor forms the basis of individual identification. Human scent is persistent, chemically stable and has low or moderate vapor pressure. This review highlights the previous studies that have been done in the past years, to sample and to analyze the combination of VOCs present in human odor. Studies have been conducted using variety of sample collection methods like solid phase micro extraction (SPME) of the gauze pad containing scent material and stir bar sorptive extraction and so on. The transfer of the scent material onto a gauze pad also has been done by various means. It has been done by direct contact with the skin or evidence articles, using Scent Transfer Unit (STU), or by swiping the surface containing the scent with the gauze pad. The subsequent analysis of the extracted scent compounds were done mostly using separation technology using the gas chromatography coupled with mass spectrometer. Some studies have also done the study using electronic nose. All the analytical studies indicate that human scent analysis is a viable method that can be used to identify human.

Labor: The post-anthropocentric body ‘at work’

Article

Apr 2020

Paul Vanouse

The post-anthropocentric body serves as host to a myriad of flows, forces, metabolisms, behaviours and perhaps performances. ‘Our’ microbiota, the microbes that live upon or within ‘our’ human tissues and fluids, orchestrate these activities. The work of such non-human agents living as ‘micro performers’ on the human epidermis is the focus of my artwork, Labor. Labor is a dynamic, multi-sensory art installation that endeavours to re-create the scent of human exertion. There are, however, no people involved in making the smell – it is created by bacteria propagating in the three large bioreactors in the artwork. Each bioreactor incubates a species of human skin bacteria responsible for the primary scent of sweating bodies. Human sweat in itself is odourless: it is these bacteria feeding upon the components of ‘our’ sweat that creates volatile, odiferous chemical compounds that ‘we’ associate with sweat and physical effort. Labor reflects upon ‘our’ changing understanding of what ‘we’ are. Microbes in and on the human body vastly outnumber human cells and help regulate many of ‘our’ bodily processes, from digestion and immunity to emotional and physiological responses, like sweating. ‘Our’ microbiota is integral to who and what ‘we’ are, and complicates any simplistic sense of (an indivisible) self. Likewise, the smell of the perspiring body is not just a human scent, unless ‘we’ are willing to redefine what ‘we’ mean by human. Whereas a traditional, anthropocentric worldview considers all activities of, on and within the human body as unified human activities, a contemporary, post-anthropocentric perspective suggests that humans are not only hosts to other organisms, but that these are collaborative, symbiotic agents of ‘our’ human identity. The artistic research carried out and its resulting artwork Labor charts how coordinated microbial performances across the human epidermis undermine any simplistic sense of a unified, rational, human self.

Processing of Human Body Odors

Chapter

Jan 2017

Human chemosensory signals are able to transmit a wide range of social information to conspecifics. Resulting from the interaction of several genetic and physiological processes (e. g., metabolic, immune, nervous), each individual produces a unique odor signature. The central processing of such chemosignals by conspecifics modifies physiological, behavioral, and psychological responses. To illuminate the importance of this mode of communication, we describe how humans produce, decode, and respond to warning chemosignals. Behavioral evidence highlighting the cognitive and emotional consequences of body odor communication will be discussed. Special attention will be devoted to the current understanding of human body odor neural processing. After an overview on the topic, we discuss the role that social chemosignals may have in our everyday life in health and disease.

Olfato e crime: implicações do reconhecimento de odores corporais na Psicologia Forense.

Thesis

Full-text available

Mar 2016

Laura Alho

RESUMO: A resolução de crimes culmina muitas vezes com a identificação de um ofensor por parte da vítima. No entanto, tem sido verificado que as testemunhas oculares e auriculares são altamente falíveis, o que se tem revelado um tema de preocupação e de discussão entre investigadores forenses e entidades policiais. Uma vez que as investigações têm incidido maioritariamente nos sentidos da visão e da audição, propusemos uma nova linha de investigação que pretende estudar a possibilidade de o olfato também poder ser considerado na resolução de crimes. Em determinadas condições, as observações feitas pelas vítimas acerca do odor do ofensor podem desempenhar um papel determinante na fase investigativa do processo. A presente tese propõe como linha de investigação o “testemunho olfativo”, pretendendo perceber (i) a capacidade dos humanos na identificação de odores corporais de estranhos em alinhamento (um paradigma semelhante aos testemunhos ocular e auricular), (ii) a memória olfativa em contexto emocional e em contexto neutro, (iii) os efeitos de algumas variáveis (de sistema e estimadoras) na identificação do odor-alvo em alinhamento. Todos os estudos apresentam, de uma forma geral, a mesma metodologia: exposição a vídeos reais (de crime ou neutros) e a apresentação simultânea de um odor corporal que é informado ser do elemento do sexo masculino que se vê no vídeo. Após uma pausa de 15 minutos, é apresentado um alinhamento com odores onde o odor-alvo está ou não presente. A metodologia foi ajustada especificamente para cada estudo. O Estudo 1 explorou o paradigma do testemunho ocular num contexto emocional (crime) e num contexto neutro (n = 80), com uma tarefa de reconhecimento forçada (i.e., o odor-alvo estava sempre presente). Os resultados demonstraram que em ambas as condições, o reconhecimento foi realizado acima do acaso, tendo sido verificado um desempenho estatisticamente significativo entre a condição crime (68%), comparativamente com a condição neutra (45%) (p ≤ .05). O Estudo 2 testou os efeitos do intervalo de retenção apenas na condição emocional (crime). Foi utilizado um intervalo de retenção curto (IRC, 15 minutos) e um intervalo de retenção longo (IRL, 1 semana). Os resultados mostraram um decréscimo na identificação na condição IRL. No IRC, os participantes foram capazes de identificar o odor-alvo acima do acaso (p ≤ .05). Ao fim de uma semana, a taxa de acerto não se diferenciou da probabilidade do acaso (p > .05). O Estudo 3 explorou os efeitos do tamanho do alinhamento na condição emocional. Foram apresentados alinhamentos de 3, 5 e 8 odores corporais. Os resultados revelaram que nas três condições o reconhecimento foi feito acima do acaso (p ≤ .05). No entanto, à medida que o alinhamento aumenta, a proporção de respostas corretas diminui, sugerindo que em alinhamentos pequenos o reconhecimento é mais eficaz. O Estudo 4 explorou o tipo de aprendizagem (acidental vs. intencional) na condição emocional (crime), com instruções diferenciadas para ambas. Os resultados mostraram a inexistência de diferenças significativas entre as condições, propondo que o reconhecimento olfativo não sofre interferências com as instruções e com o tipo de aprendizagem relativa ao odor-alvo no momento da codificação. O reconhecimento em ambas foi significativamente acima do acaso (p ≤ .05). O Estudo 5 manipulou a presença e a ausência do odor-alvo em alinhamentos de 5 odores corporais, na condição crime e na condição neutra. Os resultados revelaram que a memória olfativa parece funcionar melhor em alinhamentos onde o odor-alvo está presente. Uma vez mais, o reconhecimento em ambas as condições foi acima do acaso (p ≤ .05), verificando-se um desempenho superior na condição crime, o que corrobora e replica os resultados do Estudo 1. Finalmente, o Estudo 6 explorou o tipo de alinhamento (simultâneo vs. sequencial), manipulando a presença e a ausência do odor-alvo, em ambas as condições (crime e neutra). Foi possível identificar o odor-alvo, acima do acaso (p ≤ .05) nos dois tipos de alinhamento e o desempenho foi superior nos alinhamentos que têm o odor-alvo presente. Foram realizadas análises agregadas de todos os estudos desenvolvidos de forma a perceber o efeito de variáveis como o sexo dos participantes, a posição serial do odor-alvo em alinhamento, o efeito das emoções negativas (stresse e ansiedade), e o efeito da confiança reportada na identificação olfativa. Os resultados não revelaram diferenças entre sexos no reconhecimento de odores para nenhuma condição. No que diz respeito à posição serial, assiste-se a um efeito de primazia nos alinhamentos simultâneos, mas não se assiste a nenhum efeito nos alinhamentos sequenciais, provavelmente devido ao tipo de instruções e ao tipo de julgamento diferenciado inerentes a cada tipo de alinhamento. Relativamente aos níveis subjetivos de stresse e de ansiedade, os participantes da condição emocional reportaram níveis mais elevados em todas as medidas aplicadas antes e depois da tarefa, comparativamente com os participantes da condição neutra. No entanto, apesar das diferenças, a média dos níveis reportados é baixa, pelo que não se pode inferir que os participantes experienciaram emoções negativas fortes que pudessem afetar o reconhecimento. Finalmente, os níveis de confiança dos participantes da condição crime foram superiores aos da condição neutra. No entanto, não existe uma correlação significativa entre os níveis de confiança e a precisão das respostas. Pela primeira vez na literatura científica, mostrou-se que o reconhecimento de indivíduos através do odor corporal é possível (e significativamente acima do acaso) em alinhamentos com cinco odores corporais, onde o odor-alvo está presente. O ser humano é capaz de fazer a identificação quer numa condição emocional, quer numa condição neutra. No entanto, o reconhecimento na condição emocional parece ser potenciado, sugerindo que a emoção negativa associada a esse evento pode intensificar a recordação do odor em tarefas posteriores de reconhecimento. No entanto, apesar destes resultados interessantes e promissores, importa realçar que é necessária cautela na transposição para o contexto real. Para que o testemunho olfativo seja aplicado no terreno, ainda há um longo percurso pela frente. Ainda assim, este projeto de investigação demonstrou que o olfato pode ser uma ferramenta útil e efetiva em contextos forenses e que merece ser explorado em investigações futuras. ABSTRACT: The majority of criminal investigations frequently culminates in the identification of an offender by the victim. However, it has been shown that eye- and earwitnesses are highly fallible, which is proving a topic of concern and discussion among forensic investigators and law enforcement agencies. Since the research has mainly focused on the senses of sight and hearing, herein we proposed a new line of research that aims to study the possibility of olfaction to be considered in criminal investigations. Under certain conditions, the observations made by victims about the offender's body odor can play a decisive role in the investigative procedure. This thesis presents as a new research line the "nosewitness identification," intending to investigate (i) the ability of humans to identify body odors of strangers in lineups (a paradigm similar to that used in eye- and earwitnesses), (ii) the olfactory memory in neutral and emotional contexts (crime), (iii) the effects of some system and estimator variables in the identification of the culprit odor in lineups. Generally, all the presented studies had the same methodology: exposure to real videos (crime or neutral) and the simultaneous presentation of a body odor that was informed to be from the male seen in the video. After 15 minutes, a lineup with odors was presented in which the culprit odor was present or not. The methodology was adjusted specifically for each study. Study 1 explored the paradigm of eyewitness testimony in an emotional (crime) and a neutral context (n = 80), in a forced-choice recognition task (i.e., the culprit odor was always present). The results showed that in both conditions, the identification was performed above chance level, showing a statistically diference in the crime condition performance (68%) compared to the neutral one (45%) (p ≤ .05). Study 2 tested the effects of retention interval only in the emotional condition (crime). A short retention interval (SRI, 15 minutes) and a long retention interval (LRI, 1 week) were used. The results showed a decrease in the identification in the LRI condition. In the SRI, participants were able to identify the culprit odor well above chance (p ≤ .05). However, after one week, the correct identification rate was not different from the probability of chance level (p > .05). Study 3 explored the effects of the lineup size on the emotional condition. Lineups with 3, 5 and 8 body odors were presented. The results showed that the correct identifications were above chance in all conditions (p ≤ .05). However, as the lineup increased, the proportion of correct identification decreased, suggesting that in small lineups, recognition is more effective. Study 4 explored the type of learning (intentional vs. incidental) on the emotional condition (crime), with different instructions for each one. The results showed no significant differences between conditions, suggesting that the olfactory identification did not impaired in function of the instructions and the type of learning at the encoding of the culprit odor. The correct identifications in both conditions were significantly above chance (p ≤ .05). Study 5 manipulated the presence and the absence of the culprit odor in lineups with 5 body odors, in the neutral and emotional conditions. The results showed that the olfactory memory seems to work better with lineups where the culprit odor was present. Once again, the correct identifications in both conditions were significantly above chance level (p ≤ .05), with a higher performance at the crime condition, which supports and replicates the results of the Study 1. Finally, Study 6 explored the type of lineup (simultaneous vs. sequential), manipulating the presence and absence of the culprit odor in both conditions (crime and neutral). It was possible to identify the culprit odor well above chance (p ≤ .05) in both types of lineup. Moreover, the performance rate was higher in lineups where the culprit odor was present. Aggregated analyzes were performed for all studies in order to understand the effect of variables such as the participants’ sex, the serial position of the culprit odor in the lineup, the effects of negative emotions (stress and anxiety) and the confidence reported on nosewitness identification. The results revealed no differences between sexes in the identification of any condition. With respect to the serial position, the results showed a recency effect in the simultaneous lineups, but in the sequential lineups the results showed no significant effects, probably due to the type of instruction and to the different kind of judgment related to each lineup type. With regard to subjective levels of stress and anxiety, participants in the emotional condition reported higher levels in all measures assessed before and after the task, compared to participants in the neutral condition. However, despite the differences, the average levels were low, so it can not be inferred that participants experienced strong negative emotions that might have affected the identification. Finally, the levels of confidence of the participants of the crime condition were higher than in the neutral condition. However, there was a non significant correlation between the confidence levels and the correct identifications. For the first time in the scientific literature it was demonstrated that identification of individuals through body odors is possible (and significantly above chance) in lineups with five body odors, where the culprit odor is present. The human being is capable of identifying either in an emotional condition or in a neutral one. However, the identification in the emotional condition appears to be enhanced, suggesting that the negative emotion associated with this event can strengthen the memory of the odor in later recognition tasks. Nevertheless, despite these interesting and promising results, some caution in conveying these results to the real context is required. For the nosewitness model to be implemented in the field, there is still a long way ahead. Still, this research project has shown that smell can be an useful and effective tool in forensic contexts and which deserves to be further explored.

Polyacrylic acid polymer and aldehydes template molecule based MIPs coated QCM sensors for detection of pattern aldehydes in body odor

Article

Oct 2014
SENSOR ACTUAT B-CHEM

Molecularly imprinted polymers (MIPs) have been prepared using the polyacrylic acid (PAA) as host polymer and hexanal, heptanal, and nonanal as pattern molecules. MIPs were employed as selective coating layer of quartz crystal microbalance (QCM) sensors. Hexanal, heptanal, and nonanal were opted as target chemicals after gas chromatography mass spectrometer (GC-MS) characterization of body odor samples. Transient and static response of four QCM sensors (three coated with MIPs and one with non-MIP) to target aldehydes in singly, binary and tertiary mixtures, and water at distinct concentrations have been measured. Transient responses were analyzed to compute the response time (ton), and recovery time (toff) of sensors. This result average values of ton ≈ 5s, and toff ≈ 10s to typical concentrations of target odors. The sensitivity and baseline drift of sensors were also calculated using their static response. The heptanal template molecule based MIP coated QCM exhibit improved sensitivity, reproducibility and faster response, than the rest two MIPs, and non-MIP coated QCMs. Static sensors response matrices were further processed with principal component analysis (PCA) for qualitative (visual) discrimination and support vector machine (SVM) classifier for quantitative recognition (in %) of target aldehydes: in singly, binary and tertiary mixtures. Aldehydes odor were effectively identified in principal component (PC) space. Maximum recognition rate of 89% has been achieved for three classes of binary odors, and 79% for the combination of single, binary and tertiary odor classes in 3-fold cross validation of SVM classifier.

The Evolution of Mating Preferences and Major Histocompatibility Complex Genes

Article

Full-text available

Feb 1999

House mice prefer mates genetically dissimilar at the major histocompatibility complex (MHC). The highly polymorphic MHC genes control immunological self/nonself recognition; therefore, this mating preference may function to provide "good genes" for an individual's offspring. However, the evidence for MHC-dependent mating preferences is controversial, and its function remains unclear. Here we provide a critical review of the studies on MHCdependent mating preferences in mice, sheep, and humans and the possible functions of this behavior. There are three adaptive hypotheses for MHC-dependent mating preferences. First, MHCdisassortative mating preferences produce MHC-heterozygous offspring that may have enhanced immunocompetence. Although this hypothesis is not supported by tests of single parasites, MHC heterozygotes may be resistant to multiple parasites. Journal Article

Evidence for MHC-Correlated Perfume Preferences in Humans

Article

Full-text available

Mar 2001

Fragrances have been used since at least 5000 years ago and all traditional scents are found in modern perfumes. Although perfumes are obviously involved in sexual communication, the significance of great individual differences in preference for fragrances is an evolutionary puzzle. The major histocompatibility complex (MHC) is a highly polymorphic and conserved set of genes that plays an important role in immune function in vertebrates. Both mice and humans have been shown to prefer the body odor of potential partners that have a dissimilar MHC genotype, which would result in heterozygous offspring. We tested whether individual preferences for perfume ingredients correlate with a person's MHC genotype. The human MHC is called HLA (human leukocyte antigen). A total of 137 male and female students who had been typed for their MHC (HLA-A, -B, -DR) scored 36 scents in a first test for use on self (“Would you like to smell like that yourself?”) and a subset of 18 scents 2 years later either for use on self or for a potential partner (“Would you like your partner to smell like that?”). An overall analysis showed a significant correlation between the MHC and the scorings of the scents “for self” in both tests. In a detailed analysis we found a significant interaction of the two most common HLAs with the rating of the 36 scents in the first study as well as with the 18 scents in the second study when evaluated for self. This result suggests that persons who share, for example, HLA-A2, have a similar preference for any of the perfume ingredients. The significant repeatability of these preferences in the two tests showed that the volunteers that had either HLA-A1 or HLA-A2 were significantly consistent in their preferences for the perfume ingredients offered. Hardly any significant correlation between MHC genotype and ratings of the scents “for partner” were found. This agrees with the hypothesis that perfumes are selected “for self” to amplify in some way body odors that reveal a person's immunogenetics.

Control of mating preferences in mice by genes in the major histocompatibility complex

Article

Full-text available

Dec 1976

When a male mouse is presented with two H-2 congenic two female in estrus, his choice of a mate is influenced by their H-2 types. The term "strain preference" is used to describe the general tendency of the male population of one inbred strain to prefer two female of one H-2 type rather than another. The term "consistency of choice" is used to describe the added tendency of particular two males of one inbred strain, in sequential mating trials, to prefer two females of the H-2 type they chose in previous trials. Statistical analysis showed trends in the data that support the following conclusions: (a) The choice is made by the male, not the female. (b) The strain preference of two males may favor two females of dissimilar H-2 type (four of six comparisons), or of similar H-2 type (one of six comparisons). (c) Consistency of choice does not always correspond with strain preference. In one of six comparisons of H-2 genotypes there was no strain preference but pronounced consistency of choice by individual two male. This suggests memory, but fortuitous bias is not excluded. (d) Strain preference of the same male population may favor two male of the same or a different H-2 type, depending on which different H-2 type is offered as the choice alternative to self. These findings conform to a provisional model in which olfactory mating preference is governed by two linked genes in the region of H-2, one for the female signal and one for the male receptor. These mating preferences could in natural populations serve the purpose of increasing the representation of particular H-2 haplotypes or of maintaining heterozygosity of genes in the region of H-2.

Evidence for balancing selection at HLA

Article

Jul 1983
GENETICS

HLA data from the A and B loci for 22 populations were compared with the neutrality expectations from Ewens' sampling theory. In 25 of 44 cases, there was significantly less homozygosity than expected. Although a number of factors can affect homozygosity in this manner, upon close examination only symmetrical balancing selection appears to be consistent with these data.

Control of mating preferences in mice by genes in the major histocompatibility complex

Article

Nov 1976

K. Yamazaki

When a male mouse is presented with two H-2 congenic two female in estrus, his choice of a mate is influenced by their H-2 types. The term "strain preference" is used to describe the general tendency of the male population of one inbred strain to prefer two female of one H-2 type rather than another. The term "consistency of choice" is used to describe the added tendency of particular two males of one inbred strain, in sequential mating trials, to prefer two females of the H-2 type they chose in previous trials. Statistical analysis showed trends in the data that support the following conclusions: (a) The choice is made by the male, not the female. (b) The strain preference of two males may favor two females of dissimilar H-2 type (four of six comparisons), or of similar H-2 type (one of six comparisons). (c) Consistency of choice does not always correspond with strain preference. In one of six comparisons of H-2 genotypes there was no strain preference but pronounced consistency of choice by individual two male.This suggests memory, but fortuitous bias is not excluded. (d) Strain preference of the same male population may favor two male of the same or a different H-2 type, depending on which different H-2 type is offered as the choice alternative to self.These findings conform to a provisional model in which olfactory mating preference is governed by two linked genes in the region of H-2, one for the female signal and one for the male receptor. These mating preferences could in natural populations serve the purpose of increasing the representation of particular H-2 haplotypes or of maintaining heterozygosity of genes in the region of H-2.

Good-genes effects in sexual selection

Article

Jan 1999

The magnitude of the effect of good genes as a viability benefit accruing to choosy females remains a controversial theoretical and empirical issue. We collected all available data from the literature to estimate the magnitude of good-genes viability effects, while adjusting for sample size. The average correlation coefficient between male traits and offspring survival in 22 studies was 0.122, which differed highly significantly from zero. This implies that male characters chosen by females reveal on average 1.5% of the variance in viability. The studies demonstrated considerable heterogeneity in effect size; some of this heterogeneity could be accounted for by differences among taxa (birds demonstrating stronger effects), and by differences in the degree of mating skew in the species (high skew reflecting stronger effects). Although these results suggest that viability-based sexual selection is widespread across taxa, they indicate that the effect is relatively minor. Finally, there was also an effect of publication year in that the more recent studies reported reduced effects. This may reflect publication biases during paradigm shifts of this debated issue, but it should also be recalled that the studies have only partly estimated the full fitness consequences of mate choice for offspring.

Good-genes effects in sexual selection

Article

Jan 1999

The magnitude of the effect of good genes as a viability benefit accruing to choosy females remains a controversial theoretica and empirical issue. We collected all available data from the literature to estimate the magnitude of good–genes viabilit effects, while adjusting for sample size. The average correlation coefficient between male traits and offspring survival i 22 studies was 0.122, which differed highly significantly from zero. This implies that male characters chosen by females revea on average 1.5%of the variance in viability. The studies demonstrated considerable heterogeneity in effect size; some of thi heterogeneity could be accounted for by differences among taxa (birds demonstrating stronger effects), and by difference in the degree of mating skew in the species (high skew reflecting stronger effects). Although these results suggest that viability–base sexual selection is widespread across taxa, they indicate that the effect is relatively minor. Finally, there was also a effect of publication year in that the more recent studies reported reduced effects. This may reflect publication biases durin paradigm shifts of this debated issue, but it should also be recalled that the studies have only partly estimated the ful fitness consequences of mate choice for offspring.

Brown JL.. A theory of mate choice based on heterozygosity. Behav Ecol 8: 60-65

Article

Jan 1997

Jerram L. Brown

In theories of mate choice that rely on genetic benefits, the nature of the ''good genes'' involved has received little attention. A review of genetic studies of mate choice in a variety of species and situations suggests that individual heterozygosity is more important than previously realized. Females are predicted to value heterozygosity in their offspring and under some conditions in their males. The expression of vigor, condition-sensitive ornaments, and symmetry in males may be a direct reflection not of ''good genes'' but of individual heterozygosity at key loci or at many loci. Like sexuality itself, mate choice based on heterozygosity and genic diversity may be an adaptation that favors the production of diverse and superior competitors. Female choice is made meaningful by sexuality and the adaptive value of choice probably depends on some of the same factors that maintain sexuality.

MHC-Heterozygosity and human facial attractiveness

Article

Feb 2005
EVOL HUM BEHAV

Females gain direct or indirect fitness benefits by choosing between males with traits indicating "good genes," but we usually know very little about the nature of these genes. However, it has been suggested that genetic quality may often be defined as heterozygosity at certain loci. Here, we show that heterozygosity at three key loci in the major histocompatibility complex (MHC) is associated with facial attractiveness: Faces of men who are heterozygous at all three loci are judged more attractive by women than faces of men who are homozygous at one or more of these loci. MHC genes code for proteins involved in immune response. Consistent with this function, faces of MHC heterozygotes are also perceived to be healthier. In a separate test, in the absence of any other cues, patches of skin from the cheeks of heterozygotes are judged healthier than skin of homozygotes, and these ratings correlate with attractiveness judgements for the whole face. Because levels of MHC similarity can influence mate preferences in animals and humans, we conducted a second experiment with genotyped women raters, finding that preferences for heterozygosity are independent of the degree of MHC similarity between the men and the female raters. Our results are the first to directly link facial attractiveness and a measure of genetic quality and suggest a mechanism to help explain common consensus concerning individual attractiveness. In a relatively monogamous species like humans, evolutionary benefits from choosing heterozygous mates could include prolonged parental care and reduced risk of contracting disease for females and their offspring. (c) 2005 Elsevier Inc. All rights reserved.

Reply from C. Wedekind and T. Seebeck

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