Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.

 

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Birth Month and Maturation Rates


"In a large representative sample of young men [7380 in France], no clearly significant relationship between handedness and birth order or season of birth was found; the trend was opposite to that claimed be Bakan (1971) and Badian (1983). (Dellatolas, G., Curt, F., Lellouch, J. (1991) Birth order and month of birth are not related with handedness in a sample of 9370 young men. Cortex 27 (1): 139)

"A statistically significant inverse relationship was found between mean monthly temperature 9 mo. prior to delivery and 7,312 live births in a midwestern community. A curvilinear relationship fit the data more closely than a linear one, suggesting both extremely cold and hot weather were related to the birth rate 9 mo. later. Illegitimate and legitimate births followed nearly the same pattern. Marriages and the number of births 9 or even 10 mo. later were not related. Apparently the weather, particularly cold weather, has a powerful influence on behavior resulting in conception. ... Support for Hypothesis 3 was gained by looking up the highest and lowest monthly totals of live births for the previous 20-yr. period. Consistently the lowest month was around February (June conception) and the highest months fell around September (January conception)." (Sherrets S (1979) Weather and human conception. Psychological Reports 44: 1241) [if light is the variable, then when T is lowest in winter, sperm production may be at its height]

See P.H. Jongbloet season of birth papers (there is a bunch)

Higher T males, at this point in our evolution, evidenced increasingly asymmetrical brain lateralization. Geschwind and Galaburda (1987) hypothesize that testosterone is the primary agent responsible for variations in cerebral lateralization. The timing of the relative levels of T is vitally important to understanding variations in language facility. The absence of light has an effect on the pineal gland which results in a diminution of T production (Geschwind & Galaburda, 1987). Most people in temperate zones have lowered T in winter and raised T in summer. It is hypothesized that this pattern was established in equatorial regions according to the diurnal cycle (Geschwind & Galaburda, 1987). Changes in migration patterns away from equatorial regions, perhaps to southern Africa or into the Eurasian continent, could have placed humans at a latitude where symmetrical brains became more lateralized as a result of the changes in light and its influence on the pineal gland which regulates testosterone. Seasonal fluctuations in light hypothetically also caused asymmetrical cerebral lateralization at conception and during gestation (zygote & uterine selection) if male T is high at the point of sperm production or if female T is low during the phase of gestation when developmental rates for the fetus are set. The evolution of language from symbol to sign was occurring during the same period. The increased lateralization made further dissociation more likely which made possible the transition into sign, and the split consciousness we identify as "thought". Other potential triggers to increased lateralization could have included dietary changes or ceremonial natural inebriants. (Lehman A & Bernsten M (1999) Evolution and the Structure of Health and Disease. web link)

[citations removed] [Vermont 1981-1985] "In our sample of alcoholic men: (a) significantly more LH men were first-born; (b) significantly more men either LH or having a LH first-degree relative had an alcoholic father; (c) the RH men showed a slightly increased frequency of having an alcoholic mother or maternal grandfather; and (d) the RH men, particularly those having a maternal family history of alcoholism, were born more frequently than expected in summer and fall. This report indicates that the LH individuals in our sample were hospitalized more frequently than expected during October, a finding possibly related to Irwin's hypothesis. ... Twenty-four percent (10/42) of the LH individuals (seven of 32 men and three of 10 women) were hospitalized during October, vs 7% (19/278) of the RH individuals. .... The RH admissions were distributed equally throughout the year (7-10% per month; expected value, 8%). Stated another way, 13% of the sample were LH and so the expected percent of LH admissions during any month is also 13%. During October, however, 34% (10/29) of the admissions were LH, vs 11% (32/291) during the rest of the year (P<0.005, as above). The only other month with an excess of LH admissions was May, during which 23% (6/26) of the admissions were LH." London, WP (1986) Month of hospitalization of left-handed substance abusers. Neuropsychologia 24: 455)

"Handedness in family members was also tabulated in our study and, unexpectedly, asthmatic mothers, but not fathers, reported a particularly high percentage of their childen to be left-handed. This finding was corroborated in a study (Weinstein, Gurvitz, Greenberg, Weinstein, Solomon, Subbaiah, * Pieper, 1992) in which handedness was tested in 351 children of 139 asthamatic mothers. Left-handedness in offspring did not appear to be related to severity of asthma or to medication taken during pregnancy." (Weinstein, R.E., Lobocki, C.A., & Pieper, D.R. (1994) Allergy and the Geschwind-Behan-Galaburda Model. Brain and Cognition 26: 182)

"Also, specific congenital anomalies with a peak seasonality in March or April in the United States include cleft lip-cleft palate, hypospadias, and positional foot defects." (Torrey EF, Torrey BB, Peterson MR (1977) Seasonality of schizophrenic births in the United States. Archives General Psychiatry 34: 1070)

"The birth months of persons later diagnosed as schizophrenic were studied. Data were collected from 19 states on 53,584 schizophrenics born between 1920 and 1955. The controls were the general births in the same states for the same years. A highly significant peak in schizophrenic births was found from December and May, most marked in March and April. The seasonality was stronger in New England and the Midwest than in the South. Previous studies of schizophrenic births are also reviewed. The cumulative evidence would appear to establish more firmly a winter and spring seasonality of schizophrenic births in northern Europe and the eastern United States. Selection of patients, nutritional factors, environmental factors, genetic factors, and infectious agents are discussed as possible etiologic explanations." (Torrey EF, Torrey BB, Peterson MR (1977) Seasonality of schizophrenic births in the United States. Archives General Psychiatry 34: 1065)

[citations removed] "Within the past three years, however, well-controlled studies have been published verifying a winter and spring excess of schizophrenic births in northern European countries. Statistically significant excesses for January through March were found by Hare et al for 5,139 schizophrenic births in Denmark; and by Odegard for 12,917 schizophrenic births in Norway. Dalen, in two Swedish samples totaling 28,008, found a significant excess of schizophrenic births for January through April. In South Africa, a Southern Hemisphere country with reversed seasons, Dalen and Roche reported on a sample of 2,947 with a significant excess of schizophrenic births for May through October, more marked among females." (Torrey EF, Torrey BB, Peterson MR (1977) Seasonality of schizophrenic births in the United States. Archives General Psychiatry 34: 1065)

"There are two exceptions to this general pattern. The August schizophrenic birth rate is significantly elevated for New England as a whole. On close analysis it is found that there are slight elevations in August for all the New England states, but no single state approaches statistical significance; this regionally significant elevation, then, may represent chance variation. The other exception is the significant elevations found in June (South Carolina) and July (North Carolina and Georgia) in the coastal South Atlantic states. Other southern states do not reflect this pattern, and the South as a whole is significantly elevated for June solely on the strength of the South Carolina elevation. Since this deviation is found in three contiguous states and nowhere else, it may represent a particular pattern of schizophrenic births in these states." (Torrey EF, Torrey BB, Peterson MR (1977) Seasonality of schizophrenic births in the United States. Archives General Psychiatry 34: 1067)

"The only previous American study in which there are data on a single state also covered by the current study is Petersen's 1934 analysis of schizophrenic births in Illinois. Among patients born from aproximately 1860 to 1915 the maximum excess of schizophrenic births occured in March and April. The difference may represent either the different control group used by Petersen (all US births for 1917 through 1929) or it may represent a real shift in the seasonality of schizophrenic births over time." (Torrey EF, Torrey BB, Peterson MR (1977) Seasonality of schizophrenic births in the United States. Archives General Psychiatry 34: 1067)

"Girls who are left-handed as defined by each of the five tasks and by combinations of the five tasks showed a marked cyclic variation in the season of birth, with the peak invariably falling in or immediately adjacent to November (Table). Left-handed boys, however, did not display any appreciable cyclic variation in the season of birth." (Leviton A, Kilty T (1979) Seasonal variation in the birth of left-handed schoolgirls. Archives of Neurology 36: 116)

[abstract] "Rates of birth in the general population show seasonal fluctuations for reasons that are ill understood. Variations from these general population patterns have been reported for several psychiatric conditions and used as the basis for aetiological hypotheses. In this paper, the evidence for alterations in the expected seasonal fluctuation in birth dates of autistic people is evaluated. A national sample of 1435 autistic individuals and a clinic sample of 196 subjects are compared to general population figures and to 121 sibling controls. Compared with the general population, the national sample showed significant deviations from the expected rate of birth by month. In the clinic sample, differences from the anticipated monthly pattern were only evident when this sample was compared to the sibling controls. A variety of models for seasonal trends, including year quarters, temperature and sine wave forms, were fitted to these variations but no consistent picture emerged." (Bolton P, Pickles A, Harrington R, Macdonald H, Rutter M (1992) Season of birth: issues, approaches and findings for autism. J Child Psychol Psychiatry 33(3):509-30 )

[abstract] "Rates of birth in the general population show seasonal fluctuations for reasons that are ill understood. Variations from these general population patterns have been reported for several psychiatric conditions and used as the basis for aetiological hypotheses. In this paper, the evidence for alterations in the expected seasonal fluctuation in birth dates of autistic people is evaluated. A national sample of 1435 autistic individuals and a clinic sample of 196 subjects are compared to general population figures and to 121 sibling controls. Compared with the general population, the national sample showed significant deviations from the expected rate of birth by month. In the clinic sample, differences from the anticipated monthly pattern were only evident when this sample was compared to the sibling controls. A variety of models for seasonal trends, including year quarters, temperature and sine wave forms, were fitted to these variations but no consistent picture emerged." (Bolton P, Pickles A, Harrington R, Macdonald H, Rutter M (1992) Season of birth: issues, approaches and findings for autism. J Child Psychol Psychiatry 33(3):509-30 )

Somewhat like in the zebra finches, there is two periods when testosterone levels rise in male children: in the womb, from about six weeks after conception, and at puberty. As Anne Moir and David Jessel put it in a recent book, Brain Sex, the first pulse of hormone exposes the photographic negative; the second develops it. This is a crucial difference fro the way the hormone affects the body. The body is masculinized by testosterone from the testicles at puberty, whatever its womb experience. But not the mind. The mind is immune to testosterone unless it was exposed to a sufficient concentration (relative to female hormones) in the womb. It would be easy to engineer a society with no sex difference in attitude between men and women. Inject all pregnant women with the right dose of hormones, and the result would be men and women with normal bodies but identical feminine brains. War, rape, boxing, car racing, pronography, and hambergers and beer would soon be distant memories. A feminist paradise would have arrived. (Ridley 1993: 254-6, The Red Queen) [This quote suggests that feminity as suggested by Turner's syndrome, is a default position. It takes testosterone to establish male features. Could there be an automatic neotenous direction to evolution in the event that testerone decreases?]

"Leviton and Kilty (1979a) also investigated seasonal variation in births of left-handers, and found a peak in left-handedness among school girls born in or immediately adjacent to November, but no appreciable seasonal variation among boys. With college students as subjects, Hicks, Dusek, Larsen and Pellegrini (1980) were unable to replicate the findings of Leviton and Kilty." (Badian, N.A. (1983) Birth order, maternal age, season of birth, and handedness. Cortex 19 (4): 452)

"The most striking finding was that an excess of RH men were born during June through November, the six months showing the most births of RH men. Sixty-one percent (103/170) of the RH men were born during these six months versus 50% (61/122) of the women and the LH men ..." London, W.P. (1987) Alcoholism: theoretical consideration of season of birth and geographic latitude. Alcohol 4 (2): 128)

"The peak months for the birth of nonright-handed boys were November (27.5 percent) and September (25.0 percent). Nonright-handedness was increased for boys born in the fall and winter months, September through February (61/290 = 21.0 percent), compared with those born in the spring and summer months, March through August (36/302=11.9 percent). ... For girls, the highest frequency of nonright-handedness occurred for February, July, and August births, and lowest for June and October, but no seasonal trend was apparent." (Badian, N.A. (1983) Birth order, maternal age, season of birth, and handedness. Cortex 19 (4): 457-8)

"As a further example, the schizophrenic birth rate is elevated for the winter and spring months in North America and northern Europe, but in the New England states it is elevated also for August (Torrey et al., 1977).(Badian, N.A. (1983) Birth order, maternal age, season of birth, and handedness. Cortex 19 (4): 461)

"Several neurological and immune phenomena, many of which are associated with cerebral laterality, show an atypical seson of birth pattern. For example, excess of births during the winter and spring have been described for individuals with schizophrenia and the bipolar disorder.(5,10), Klinefelter's and Turners syndromes (16), cleft lip and palate (10) and neural tube defects (12), thyroid goiter or diabetes melitus (10) and twins (10) and "eminent" people (12). In other studies, autistic males were born more frequently during the spring and summer (3,17), individuals with Down's sydrome during the spring and autumn (14) and those with mental retardation of Hodgkin's disease during the summer (10). In the Prader-Willi syndrome (characterized by infantile hypotania, mental deficiency, early childhood obesity, short stature, small hands and feet and hypogonadism), 50% of those affected show a deletion of paternal chromosome 15, and a significant excess of those showing the chromosomal deletion were born during the autumn (6). In other studies, left-handed (LH) males (1) and individuals with rheumatoid arthritis or systemic lupus erythematosis (10) were born more frequently during September through February, and individuals allergic to pollen were born more frequently in the spring (7). A small study of alcoholic men and women showed excess births during August through January (36), but other studies of alcoholic individuals have not shown an atypical season of birth pattern (10). Cerebral laterality has been related to alcoholism (2,8, 19-23, 30), schizophrenia (15), autism (27), mental retardation (13), Klinefelter's (24) and Turner's (34) syndromes, cleft lip and palate, neural tube defects, twinning, and immune disorders (12). These considerations suggest that neurological or immune phenomena associated with cerebral laterality might also show an atypical seson of birth pattern, and vice versa. Alcoholism has been associated with cerebral laterality (2, 8, 19-23, 30). Several studies have shown an increased frequency of left-handedness (2, 8, 19, 23, 30) that has been associated with less favorable treatement outcome (20,30). In addition, in our sample of alcoholic men, being LH or having a LH first-degree relative was associated with having and alcoholic father (19,22), being LH was associated with being first born (19), and being right-handed (RH) was associated with having an alcoholic mother or maternal grandfather (22). Furthermore, boys reared away from their alcoholic fathers, show lower verbal but not performance IQ scores (11), and 4-year-old children of alcoholic fathers as compared with control children show delayed language development (32); both findings suggest left-hemisphere dysfunction." (London, W.P. (1987) Alcoholism: theoretical consideration of season of birth and geographic latitude. Alcohol 4 (2): 127)

[abstract] "OBJECTIVE: Variations in month of birth were examined in patients with infantile autism to test the hypothesis that birth in a particular month may be a risk factor for this disorder. METHOD: Data for autistic patients registered with the National League for Autism in Israel (N = 188) during the years 1964-1986 were compared with data on monthly distribution of live births in Israel for the corresponding period. RESULTS: After risk ratio estimates were computed for children born with infantile autism for each month, a significant increase was observed for children born in March and August. This association was true for each year throughout the study. An additional finding was a significantly higher rate of birth of autistic children in the years 1970-1976. CONCLUSIONS: This study, although made in a different climatic area than three earlier studies, further emphasizes the earlier findings that March and August births are a risk factor for development of autistic disorder." (Barak Y, Ring A, Sulkes J, Gabbay U, Elizur A (1995) Season of birth and autistic disorder in Israel. Am J Psychiatry 152(5):798)

[abstract] "More than 250 studies, covering 29 Northern and five Southern Hemisphere countries, have been published on the birth seasonality of individuals who develop schizophrenia and/or bipolar disorder. Despite methodological problems, the studies are remarkably consistent in showing a 5-8% winter-spring excess of births for both schizophrenia and mania/bipolar disorder. This seasonal birth excess is also found in schizoaffective disorder (December-March), major depression (March-May), and autism (March) but not in other psychiatric conditions with the possible exceptions of eating disorders and antisocial personality disorder. The seasonal birth pattern also may shift over time. Attempts to correlate the seasonal birth excess with specific features of schizophrenia suggest that winter-spring births are probably related to urban births and to a negative family history. Possible correlations include lesser severity of illness and neurophysiological measures. There appears to be no correlation with gender, social class, race, measurable pregnancy and birth complications, clinical subtypes, or neurological, neuropsychological, or neuroimaging measures. Virtually no correlation studies have been done for bipolar disorder. Regarding the cause of the birth seasonality, statistical artifact and parental procreational habits are unlikely explanations. Seasonal effects of genes, subtle pregnancy and birth complications, light and internal chemistry, toxins, nutrition, temperature/weather, and infectious agents or a combination of these are all viable possibilities." (Torrey EF, Miller J, Rawlings R, Yolken RH (1997) Seasonality of births in schizophrenia and bipolar disorder: a review of the literature. Schizophr Res 28(1):1-38)

It is possible that schizophrenia is more common in individuals who have spent the first six months of pregnancy under maximal hormonal influences. Mental defectives are also more likely to be born at the beginning of the year. On the other hand, many extensive studies of the birth months of eminent people have shown that they too tend to be born predominantly early in the year; even more consistently, the rate of such births is low in the midsummer months of July and August (Peterson 1979). (In all of these studies the data have been corrected for the normal yearly pattern of births.)" (Geschwind & Galaburda 1987: 219-20, Cerebral Lateralization)

"The time of conception is another nongenetic random variable that may well significantly influence laterality. Seasonal effects have often been considered narrowly. The fact that schizophrenics are more likely to be born in January than July, a finding documented repeatedly has often been interpreted as a result of increased susceptibility of newborn infants to virus infection in the winter. There are many other possibilities, however. Consider, for example, changes in sex hormones with day length. The pineal gland, activated in the dark months, tends to suppress gonadal hormonal production. When it is suppressed, during periods of long days, sex hormones rise. We have already alluded to Badian's (1983) report of a higher rate of nonrighthandedness in males conceived from December through May (days being shortest on December 21 and increasing in length for the following six months). A pineal role in laterality has no direct experimental support, but it certainly deserves study."
(Geschwind & Galaburda 1987: 135-6, Cerebral Lateralization)

"A corollary of our hypothesis is that hormonal effects on the brains of offspring may vary with the time of conception. The activity of the pineal gland changes seasonally with alterations in day length. As a general rule, during the dark winter months the pineal becomes active and suppresses both ovaries and testes, whereas in the summer it is inactive and sex hormone levels are higher. For this reason many animals bear young in the spring, an advantageous situation since temperature and food supplies are more suitable for survival. An example of such seasonal modulation of hormonal effects on the brain is observed in the HVc nucleus of the singing bird (Nottebohm 1981). This description of pineal physiology is, however, somewhat oversimplified. An animal's sensitivity to light may vary through the year. Gonadal hormones may thus become activated in the spring, but as a result of loss of sensitivity to light over th summer hormone levels may diminish as fall approaches. Despite these facts, day length is a powerful influence. Thus, steers increase their weight more rapidly in the winter when artificial light is supplied to lengthen the day. This light-enhanced growth of muscle mass does not take place if the bull is castrated, suggesting that the effect of light is mediated through a rise in testosterone effect (Tucker and Ringer 1982).....If pineal effects on sex hormone levels are important, then the birth months of lefthanders, and of those with learning disorders, might not be uniform throughout the year, since fetuses conceived at different seasons might be subjected to very different hormonal environments. These effects should differ in the Northern and Southern Hemispheres and at the equator, although other factors, such as variations in the ethnic composition of populations, would also have to be considered. Data are still very sparse. Badian (1983) found that in males born in each of the six months beginning in September, the rate of nonrighthandedness was higher than that found in any of the other six months, but no clear trend was observed for female births." (Geschwind & Galaburda 1987: 116-7, Cerebral Lateralization)

"When the day is artificially lengthened in the winter, Holstein cows increase their milk production and steers gain weight faster (though not when castrated, which strongly suggests that the testes play a role). It is likely that the pineal gland exerts a major control in this regard. During the dark months it is active and suppresses the gonads, but during the longer days it becomes inactive and the production of gonadal hormones therefore rises. This mechanism clearly makes it more likely that animals will be born in the spring, a useful adaptation since conditions of food and climate are far more favorable for survival. Sensitivity to long days appears to diminish over time, so that it is less marked by the end of the summer (Reiter 1980). Male rats raised in constant darkness show diminished sexual activity, but this is reversed by pinealectomy (Baum 1968), presumably because of the removal of pineal inhibition. The yearly cycle is not merely attended by changes in the other metabolic alterations. The hyperglycemic response to epinephrine in humans is higher in the winter than in the summer (Altschule and Siegel 1951). The golden hamster shows greater thermogenesis in response to a cold stimulus in midwinter than in midsummer (Pohl 1965). Though the yearly metabolic cycle can probably not be attributed entirely to activity of the pineal, it must play a major role. We have already noted that cyclic alteration in the production of sex hormones is likely to be important in many ways; for example, it might affect the percentage of children with anomalous dominance born at different seasons. Children conceived in March or April will spend most of their first months in utero at a time when hormones are high. Children conceived six months later, in September or October, will tend to spend their early period in utero under much lower hormonal influences. Obviously, different quarters of the year will give rise to different patterns, but adequate information regarding the outcomes is still lacking. Badian (1983) found that nonrighthandedness was twice as common among boys born in the six months beginning in September (and thus conceived from December through May) than among those born in the following six months. Furthermore the number of nonrighthanders born in each of these months was higher than the number born in every month in the other half year. Similar effects were not found in females. It is intriguing that compared to controls, rabbits raised postnatally in darkness for seven months were fond to show an increase if synaptic contact zones in the medial visual cortex and the motor cortex on the left, but not on the right (Vrensen and deGroot 1974); however, the authors are cautious in their interpretation of this. There are other possible relevant data. It has been confirmed repeatedly that schizophrenics are born predominantly in the first half of the year particularly in the first quarter. They are thus conceived between approimately April 1 and October 1, that it, predominantly during the period in which the days are longer than 12 hours. It is possible that schizophrenia is more common in individuals who have spent the first six months of pregnancy under maximal hormonal influences. Mental defectives are also more likely to be born at the beginning of the year. On the other hand, many extensive studies of the birth months of eminent people have shown that they too tend to be born predominantly early in the year; even more consistently, the rate of such births is low in the midsummer months of July and August (Peterson 1979). (In all of these studies the data have been corrected for the normal yearly pattern of births.)" (Geschwind & Galaburda 1987: 219-20, Cerebral Lateralization)

"Several neurological and immune phenomena associated with cerebral laterality also show an atypical season of birth pattern. Alcoholism is also associated with cerebral laterality. In this pilot study (n = 292), 66% of right-handed alcoholic men were born during the summer and fall (expected 52%, p less than 0.001). This finding suggests that at high latitude more right-handed men would become alcoholic because seasonal effects usually intensify with increasing latitude. In addition, in our sample of alcoholic men, left-handedness was associated with having an alcoholic father or with being first-born. Together, these findings suggest that the prevalence of alcoholism should increase with increasing latitude, and that the frequency in alcoholic men of being left-handed, first-born or having an alcoholic father should decrease with increasing latitude. The available literature tends to substantiate these correlations, but more systematic studies of season of birth and correlations with latitude in alcoholism are required." (London, W.P. (1987) Alcoholism: theoretical consideration of season of birth and geographic latitude. Alcohol 4 (2): 127)


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