Mammary number and litter size in Rodentia: The "one-half rule"

Litter size and mammary number in the mammalian order Rodentia show a significant positive correlation. Mean litter size is typically one-half the number of available mammaries, while maximum litter size approximates mammary number. Similar relationships are found in the families Muridae, Cricetidae, and Sciuridae. The relationship of litter size to mammary number is significantly different between the arboreal and terrestrial squirrels, and between the hystricomorph and nonhystricomorph rodents. Mammary number may have operated as a selective constraint on litter size over evolutionary time.

Sex differences in task performance associated with attention to ambient odor

The effects of ambient odor (pleasant, unpleasant, none); odor suggestion (present, absent); and sex of subject on mood and performance measures were explored in a 3 x 2 x 2 experimental design. A total of 40 men and 40 women performed a clerical task and a speed and accuracy task (digit deletion), filled out self-evaluations of mood, predicted performance, and rated the odor quality of the test room. Ambient odor conditions significantly affected room smell ratings, but they had no effect on performance or mood. Odor suggestion produced a significant sex-related interaction effect on the digit deletion task, irrespective of actual ambient odor. The results are discussed with respect to sex differences observed in laboratory studies and in epidemiological investigations of multiple chemical sensitivity and sick building syndrome.

Odor intensity and color lightness are correlated sensory dimensions

We previously found that untrained subjects make nonrandom color matches to odors and that the color matches are stable over time (Gilbert, Martin, & Kemp, 1996). Here we investigate further aspects of the cross-modal associations between vision and olfaction: whether perceptual dimensions of odor vary systemically with those of vision. Subjects matched Munsell color chips to five odors presented at three concentrations; they also rated odor intensity. Significant negative correlations between Munsell value and perceived odor intensity were found for three odors. The results suggest that stronger odors were associated with darker colors. The cross-modal relationship between vision and olfaction appears to be dimensional: Color lightness varies inversely with perceived odor intensity. This finding parallels the dimensional relations found between other modalities (e.g., lightness varies with loudness).

Odor perception phenotypes: multiple, specific hyperosmias to musks

Olfactory detection thresholds for 11 structurally diverse musk odorants and one non-musk odorant were obtained from 32 subjects. Hierarchical cluster analysis produced four groups of subjects. One group (n = 12) was uniformly sensitive to all musks; another (n = 16) was uniformly insensitive. Two groups of subjects contained otherwise insensitive individuals who were exceptionally sensitive to cyclopentadecanone and musk xylol (n = 2) and to delta9-hexadecenolactone and tonalid (n = 2) respectively. We propose that the latter two groups are odor perception phenotypes (MSHM1 and MSHM2) that consist of multiple, specific hyperosmias to musk odorants.

Workplace, age, and sex as mediators of olfactory function: data from the National Geographic Smell Survey

Certain medications and environmental agents are known to adversely affect chemosensation. We report data from 712,000 respondents aged 20 to 79 to the National Geographic Smell Survey that suggest that exposure to the factory workplace adversely affects the sense of smell, and that these effects interact with age. Men and women with histories of factory work reported poorer senses of smell relative to other workers. They also demonstrated objective evidence of greater impairment in odor detection. These effects were greater for men. Factory workers of all ages more frequently reported olfactory loss secondary to chemical exposure and head injury than did workers in other environments. The highest relative risk of olfactory problems secondary to head injury was in the oldest women factory workers. Thus, olfaction may behave as other senses do: Age, sex, and exposure to noxious events or agents interact to produce sensory deficits.

Life span changes in the verbal categorization of odors

An odor description task was used to explore age-related change in odor perception based on 1.19 million U.S. and Canadian respondents (ages 10-90 years) to the National Geographic Smell Survey. Respondents sampled six microencapsulated odorants and selected 1 of 11 descriptors to characterize each smell. Four odors were characterized by strong consensus endorsement of a single descriptor. This consensus weakened with advancing age, and nonmodal descriptors were endorsed more frequently. Nonmodal responses were neither randomly selected, nor systematically biased across odors. Rather, they showed odor-specific patterns of change. Together, these results suggest a marked change in odor categorization across the life span. Odor descriptor profiles were used to generate age-specific multidimensional scaling maps. Stimulus configurations were stable from the third through fifth decades. Those from the sixth through ninth decades showed major displacements for two odors, and suggest that the sweet dimension of odor quality may be particularly variable with maturation.

Hand preference and age in the United States

A survey of 1,177,507 U.S. men and women between the ages of 10 and 86 included questions regarding hand preference for writing and throwing. Three effects were observed. Individuals with at least some left motoric bias comprised a smaller percent of the population with advancing age. This finding provides large-scale confirmation of a previously described phenomenon. Among sinistrals, concordance for writing and throwing was 2.2 times as prevalent as left-writing with right-throwing, and 4.1 times as prevalent as right-writing with left-throwing. These sinistral subpopulations displayed distinct and stable prevalence prior to age 50 and changing patterns of prevalence subsequent to age 50. The results confirm a decrease with age in the prevalence of sinistrality, but indicate that age-specific rates of mixed- and left-handedness are distinct. The implications for hypotheses regarding age-related change in the prevalence of sinistrality are discussed.

Quantitative assessment of olfactory experience during pregnancy

Results of the National Geographic Smell Survey were used to investigate the effects of pregnancy on olfactory perception and odor-related behavior. The responses to test odors and survey questions of 13,610 pregnant and 277,228 nonpregnant U.S. women between 20 and 40 years of age were analyzed. In comparison to nonpregnant women, pregnant women rated their own sense of smell lower, more often rated the test odors less pleasant smelling, more often classified the test odors as inedible, were less likely to report odor-evoked memories, and used perfume and cologne less frequently. Differences in odor detection and intensity rating did not favor either group.

Reciprocity versus rhythmicity in spontaneous alternations of nasal airflow

Active anterior rhinomanometry was used to observe nasal airflow in five men and four women (ages 18-30). Measurements were obtained for each nasal passage every 5 min throughout an uninterrupted 8-hr session. Facial skin temperature from the left and right side of the face was recorded simultaneously from thermocouples. Observations were made during the months of May and June; subjects were allowed to maintain their routine diurnally active schedules prior to observation. Airflow in the two passages showed a significant negative correlation (i.e. was reciprocal) in 44% of subjects (N = 9). Autocorrelation and spectral analysis of the airflow data found evidence of periodicity in 39% of individual nostrils and 56% of subjects. Mean estimated period was 4.5 +/- 1.0 hr (range 3.5-6.0 hr). Only 22% of subjects showed statistical evidence of periodicity in both nostrils (i.e. a "nasal cycle"). Left- and right-side facial skin temperatures changed in parallel rather than reciprocally, but showed evidence of periodicity in 50% of hemifacial time series (56% of subjects), with an estimated period of 3.8 +/- 1.0 hr (range 2.3-5.0).

Sex, handedness and side of nose modulate human odor perception

Multidimensional scaling was used to analyze odor similarity judgments obtained by monorhinic (single nostril) stimulation from normal subjects (N = 52), equally partitioned by sex and handedness. Neither sex nor handedness nor side of nose appeared to alter the position of stimuli on a two-dimensional map of odor similarity. However, women produced significantly more consistent maps than men. This result was not due to differential utilization of axes in the multidimensional perceptual space, nor to differences in verbal labeling. Left versus right nostril asymmetries were significantly greater in dextrals.

Biological rhythmicity of nasal airway patency: a re-examination of the 'nasal cycle'

Rhinomanometric observations of nasal airway patency were obtained for each nasal passage every 10 min throughout an uninterrupted 8-h session. The 49 airflow observations for each nasal passage were subjected to autocorrelation analysis, a statistical technique for quantifying periodicities in a temporal sequence of observations. No significant periodicities were found in any of the 16 subjects when the autocorrelation functions were interpreted by conventional statistical criteria. However, when less stringent criteria were applied, we found suggestive evidence for rhythmicity in one (7 subjects) or both nasal passages (2 subjects). The relationship in patency between the two sides of the nose was characterized with correlation coefficients. These correlations were significantly negative in 7 subjects, indicating bilateral reciprocity of patency. In addition, the correlations were significantly positive in one, and nonsignificant in 8 subjects. Only a minority of subjects (13%) displayed the classical nasal cycle, i.e., rhythmicity in both nasal passages as well as reciprocity of patency between passages.

Olfactory discrimination of mouse strains (Mus musculus) and major histocompatibility types by humans (Homo sapiens)

A series of experiments revealed that humans can use olfaction to discriminate closely related strains of mice, differing genetically only at the major histocompatibility gene complex (H-2). In Experiment 1, subjects were asked to distinguish between the whole-body odors of live mice. In Experiments 2 and 3, the odor source was mouse fecal pellets, and in Experiments 4 and 5, the odor source was mouse urine.

Timing of parturition and postpartum mating in Norway rats: interaction of an interval timer and a circadian gate

Two temporal variables have been implicated in the timing of postpartum heat in Norway rats: time of day and time since parturition. The nature of the interaction between these variables is not clearly understood. We extend previous observations on this problem to freely behaving animals continuously videotaped during parturition and postpartum mating in a seminatural habitat. The timing of postpartum mating is best described by a model in which an interval timer is coupled to a circadian gating mechanism. Interactions between circadian and interval timing mechanisms may be widespread in the neuroendocrine control of behavior.

Postpartum and lactational estrus: a comparative analysis in rodentia

Virgin rodents exhibiting cycling estrus have traditionally been used for comparative studies of reproductive behavior. However estrus occurs in other life-history contexts, some of which differ from cycling estrus (CE) in that (a) the female is disposed to behave both maternally and sexually and (b) they result in litter overlap (i.e., the simultaneous gestation and lactation of two litters). In this report, two of these other modes of estrus are examined, with emphasis on their evolutionary and ecological implications. By means of a literature search of the order Rodentia, postpartum estrus (PPE) and lactational estrus (LE) were documented in 15 families, 71 genera, and 141 species. Analysis of these data showed that PPE and LE were nonrandomly distributed across taxa. They were statistically overrepresented in the family Cricetidae and underrepresented in squirrels (Sciuridae) and in pocket mice and kangaroo rats (Heteromyidae). Analysis of the phenotypes by which PPE and LE are achieved suggests important differences between them and CE in several parameters of female reproductive effort and breeding strategy, including maternal and copulatory behavior, optimal timing of litters, and hormonal control of heat and lactation.

Mother-weanling interactions in Norway rats in the presence of a successive litter produced by postpartum mating

When female Norway rats (Rattus norvegicus) become pregnant at the postpartum estrus they nurse this first litter concurrently with the gestation of a second litter. This second gestation is of variable length (23-31 days in this study) We investigated the behavior of mothers and their older litters around the time the second litter was born. Six female rats gave birth and were mated at the postpartum estrus. Continuous videotaped observation of each female and litter began approximately 3 days before, and continued for 3 days after the birth of the second litter. We found that suckling behavior and nest attendance by the older litter did not necessarily end when the second litter was born. When the gestation length of the second litter was short (23-25 days) older pups continued to spend time in the nest and to nurse along with their newborn siblings. These older pups also spent much time on the nest even in the absence of their mother. When gestation was long (27-31 days) older pups were weaned before the birth of the second litter and spent less time on the nest with the newborns. Stereotyped attacks by the female against her weanling age pups were seen both pre- and postpartum. This maternal aggression did not appear to deter suckling and nest attendance by the weanlings.

Conceptions of homosexuality and sodomy in Western history

This essay explores recent attempts to write the history of homosexuality and identifies two distinct approaches: the biographical approach, which reports on the private lives of individuals and charts the formation of homosexual subcultures; and the approach that studies the labeling and treatment of homosexual men and women by the heterosexual majority and examines the reasons why hatred of homosexuality increases and decreases over time. The author warns against applying modern definitions to words that have had different connotations. An an example of the possible confusion, the author discusses the two meanings of the work sodomy: unspecified sexual relations between males; and the act of anal intercourse, whether heterosexual or homosexual. Western civilization's association of the anus with evil, the devil, and bestiality is examined.