Hillson Text Ch 9 Histological Methods of Age Determination pp 207-216 and Ch 10 Biochemistry of Dental Tissues pp 217-230
I. ALTERNATIVE AGEING METHODS p 207
The most common methods of estimating age at death are based on gross inspection of the skeleton and dentition, and radiographic examination of the jaws in younger persons. Specific boney parts examined are the pubic symphysis of the pelvis, dental attrition, cranial sutures, and sternal end of the fourth rib. These are treated elsewhere in these notes. No adult ageing method is highly accurate.
Several (invasive) histological methods have been reported for teeth:
(1) Cementum layering has been reported, but has many limitations.
(2) The Gustafson technique is a composite system that estimates dental attrition, periodontosis, secondary dentin deposition, cementum apposition, root resorption, and root dentin sclerosis.
II. BIOCHEMISTRY OF DENTAL TISSUES p 217
This is a highly specialized chapter directed primarily to the skilled archaeologist and laboratory worker using highly sophisticated techniques for dental analysis.
HORMONAL, GENETIC, AND ENVIRONMENTAL FACTORS CONTROLLING GROWTH
Note: The overall format and content are based on Harrison et al Human Biology 3rd ed, 1993. References to the Cambridge Encyclopedia of Growth and Development are cited as CEGD within the text.
I. PRENATAL AND POSTNATAL PERIODS (See Harrison et al p 377 Bogin pp 173 - 190, and the articles in CEGD 4.1, 5.1, 5.2, 5.14)
A. Hormones During The Prenatal Period
Unlike what happens after birth, the majority of hormones that regulate fetal growth are synthesized locally. These hormones act directly on the cells that produce them or those located close by. The most important of these hormones are the peptide growth factors.
What about the traditional hormones and growth factors that act at a distance from the cells that produce them? The only one of importance in the regulation of fetal growth is the insulin produced by the fetal endocrine pancreas. This is because maternal insulin cannot cross the placental barrier. (Insulin is a large molecule. This is why it cannot be given orally to insulin-dependent diabetics.)
Fetal insulin regulates the synthesis of peptide growth factors.
Other hormones have little influence over intra-uterine growth. Thyroid hormones are important for the development of the nervous system. Androgens and estrogen are important for skeletal maturation and sexual differentiation, but have little role in longitudinal growth. Pituitary growth hormone becomes important only in the last weeks of gestation.
B. Hormones in the Post-natal Period
Post-natal growth arises predominantly as a result of growth hormone secretion and the final component of post-natal growth at puberty-a time of interaction between growth hormone and the gonadal steroids. As we've mentioned before, growth hormone is produced in a pulsatile fashion. Sex steroids modulate the final component of post-natal growth, namely the pre pubertal growth spurt.
What is important to know? The actions and interactions of hormones and growth factors provide a system of fine control for the regulation of growth and development. (Bogin p 174)
C. Growth After Birth
With advances in medical technology, the practicing orthodontist will increasingly encounter persons who were premature and/or low birth weight babies. What sort of growth patterns do they exhibit?
Normal intra-uterine growth is considered to be a favorable marker of fetal well being. The premature-birth and/or low-weight-at-birth infant has high energy requirements. Thus, optimal nutrition and favorable environmental conditions enable these infants to develop in a way similar to that of the full-term infant.
In the first ten days after birth the average weight loss is 7%. Weight loss is greater for later borns than for firstborns. Summer and autumn babies gain it back sooner. Premature babies regain birth weight loss more slowly. (See Krogman Ch 2)
D. Athletics and Growth
What effect does exercise and sports have on growth and development? (See CEGD 5.12 and Tanner p 135)
This is a complex issue. Talented athletes tend to be selected for their specific skills; therefore, any comparison between athletes and non-athletes must be approached with caution. For example, gymnasts tend to be shorter that the population average whereas swimmers tend to be taller than average. Ballet dancers tend to be very linear in build.
When comparisons are carefully made, what conclusions can be reached about the influence of physical activity and sport?
(1) Regular physical training and athletics have no apparent effect on attained stature and rate of growth.
(2) Body weight is influenced by regular activity. Regular physical activity does result in increased bone mass; however, in girls, exercise intensity that causes a halt in monthly periods can lead to bone loss. Restrictive diets are particularly damaging.
Regular physical exercise does reduce fatness. In young adult males, there is a greater reduction in trunk fat than in extremity fat-a benefit that is retained only as long as exercise is continued.
Adequately nourished children will grow and mature whether active or not active. Regular activity has no effect on attained height or the rate of maturation. The first menses is often delayed in young female athletes, but diet restriction may be a factor as well. Regular physical activity does help to regulate body weight, but much additional research is necessary in this field.
II. PUBERTY (See Harrison et al p 380, Bogin pp 161-162, CEGD pp 227-229 )
Adolescence marks a rather abrupt transition from childhood to physical maturity and fertility. The hormonal and hypothalmic events are complex; the interested reader is referred to CEGD article 5.15.
In these articles I have presented the conventional view that there is a close relationship between reproductive and skeletal maturation. This perception is the basis for using a hand-wrist radiograph atlas to measure developmental status.
Other ideas have emerged. One controversial theory suggests for girls, that a menstrual onset is based on achieving a minimal level of body fat. This idea has not achieved widespread acceptance.
Long term radiographic data indicated that the first menses is closely correlated with the attainment of adult external pelvic widths.
Male maturation and fertility reflect the acquisition of greater strength and competitive ability that comes withe greater size and maturity.
Menarche occurs late in the pubertal growth spurt. Monozygotic twins achieve it within two months; dyzygotic twins within nine months. The mean age of menarche has declined in industrialized countries during the past 150 years-an aspects of the secular growth trend which we treat as a separate topic elsewhere. (See CEGD p 228)
This unit revisits the nature-nurture issue. Our next major unit is about human adaptability which examines the plasticity of growth in response to environment.
The rate of development is hereditary; however, and it is influenced by diet, season, psychological stress. Growth is also influenced by socioeconomic status, giving rise to the old adage that the health of a society is reflected in the heights of its children. The specific factors in our discussion appear below.
We recognize that the expression of a gene depends on other genes and the external environment. I am reminded of the phrase 'he who has gets' when the writers say that some people benefit more from their environment than others. The nearer the environment to optimum, the better the opportunity for genes to express their maximum potential.
Genetics overall is immensely important in growth and development. (See Bogin Ch 6 and CEGD pp 121-144.) It has long been known that children tend to resemble their parents in stature, body proportions, and rate of development. The study of the genetics of growth, however, has only a fairly recent history.
Study of siblings, parents & offspring, and twins suggest a strong genetic component to growth and development.
The correlation between a child and parent is seemingly low at birth due to the influence of the intra-uterine environment, but correlation between parents and child increase after the age of two years.
The effects of genetic control on adult stature in considerable. The 95% limits of normal variation around the mean is as follows:
25 cm for unrelated persons,
16 cm for brothers, and
1.6 cm for monozygotic twins.
Studies of twins indicate that the overall shape of the post-natal growth curve, short-term variations, and 'canalization' are under genetic control. Thus, growth is target-seeking and self-stabilizing. The control of shape seems under even more rigorous control than size. Dental maturation (tooth formation, eruption timing and eruption pattern) are under strong genetic influence, though fairly independent of skeletal maturations. These findings are apparent in comparison of monozygotic and dizygotic twins.
Twin studies have attracted much interest. It might surprise you to learn that monozygotic twins often have different birth weights. There is more similarity in weight of dizygotic twins than for monozygotic twins. When fully grown, monozygotic twins are more concordant than dizygotic twins. (See Bogin p 164.) The twins often don't share equally in placental resources. After birth, however, the smaller twin tends to catch up, but if the difference at birth is severe, catch up is not complete.
What about the opposite extreme, adoption? Significant correlation exists within families when fatness is measured. Thus, social kinship has an influence on growth and development. The effect of shared familiar environment is small, however, compared to an individual's unique genetic constitution (see CEGD p 130).
(1) Genetics of growth (See Harrison et al p 382, Bogin Ch5)
The genetic control of tempo of growth is studied most directly as inheritance of age at menarche. Why? It is a concise marker in girls--acknowledged in private in our culture, but marked with ceremony in many aboriginal ones. The concordance for monozygotic twins is two months, while for dizygotic twins or sisters it is only 12 months (see CEGD p 128).
The authors in Harrison et al say that genetic factors seem important in age of menarche and control is polygenic.
Do understand that first menses seems to be delayed in many food foragers and that the modern-day First World early onset does not reflect the prehistoric human condition. Intense gymnastics, ballet training, and anorexia can delay and/or stop periods altogether. Body fat is said by many to be a factor. Some set a minimum of 17% for menses; if there is too little fat, menstrual periods do stop.
The sequence and timing of tooth development, eruption, and shedding seem under strong genetic control.
The sequence of skeletal development (we've said before) is under tight genetic control. When using a hand-wrist atlas for assessing skeletal maturation, the closer the assessment to cessation of growth, the more accurate is the prediction.
(2) Ecology and Ethnic Difference (Harrison et al p 385)
Distance charts for stature of well off Africans and Europeans show little difference. Well off Chinese and Japanese are shorter and clearly finish their growth earlier than their European counterparts. Full blooded children of immigrants early in this century showed significant gain in stature when raised in Hawaii or in the continental United States.
When there is malnourishment during childhood, the gross restriction of growth is evident.
Climate does not have a direct effect on a rate of growth; however, there are some important exceptions. Growth at high altitude is impaired (Bogin p 134 and the balance of Ch 5; also see Overfield).
In this country, well-off black girls are ahead of whites throughout the whole growth period. Extensive evidence shows that Blacks display more advanced skeletal maturity and motor skills at birth and in early years.
Permanent teeth of many African people also erupt earlier by an average of a year--another factor to consider in the use of tooth eruption tables in dental texts. The much earlier eruption of the third molars at ages 12-13 years in some East African populations is well documented. (Krogman p 161)
The growth of teeth is more resistant to malnutrition and disease than is the skeleton. Harris lines appear more readily than enamel hypoplasia or Wilson lines.
There are many studies that show that the larger the family, the slower is the growth rate of the children (Krogman p 143).
What about between-population differences in growth and development? The former Soviet Union, a vast country spanning eleven time zones was a unique 'laboratory' for bioanthropologists (see article 10.5 in CEGD). In the former USSR, there was no geographic gradient north, south, east, and west. However, almost without exception, there was a clear urban-rural gradient with the city girls being the earlier maturers. Maturation in cities was virtually the same, no matter the location. In spite of state socialism, these differences are attributed to socioeconomic differences.
The wide range of ages for menarche in present-day populations makes it difficult to make a firm conclusion about differences between ethnic groups.
These are environmental conditions that affect age of menarche (CEGD p 376): altitude, nutrition, disease, family size, and social conditions.
(3) Season of Year (Harrison et al p 385, Krogman p 146, Tanner p 110; see chart Tanner p 110; Bogin beginning p 139, CEGD pp 220-224)
Growth in height is fastest in spring and growth in weight is fastest in the fall. This has been clearly documented in Europe and North America over the past 75 years. Why are height and weight out of phase? It may be that two different factors underlie the two patterns of growth. Blind children grow cyclically, but not in synchrony with the seasons. Although I've mentioned seasonality in growth, not all children show it. The seasonal pattern for height gain is even present in children receiving synthetic growth hormone therapy. (See CEGD p 223.)
Sunshine (and vitamin D production) seem to regulate growth in height. Growth in weight seems to be endogeneous (Bogin pp 139-143).
Temperature has a significant influence on growth. Studies in mice have shown that mice raised at 65 grow as well as at 72 . Mice grown at 90 however lag far behind in growth.
Cattle take much longer to mature in Panama than they do in Iowa. Mainland American children are a bit taller than ones from the US raised in Panama.
(4) Nutrition (Harrison et al p 385 and Bogin Ch 5)
Malnutrition delays growth, as shown by famine. Children have great recuperative powers if the insult is not too long.
Girls appear better buffered than boys (you will recall the comment last week that girls are less likely to be 'bumped' off their growth trajectory).
Surrounded by food, we forget that in our past--and in many areas today, subsistence farmers face periodic food shortages. Food, culture, and growth are intertwined. We seem to be genetically equipped for periodic food deprivation.
In cattle, the fastest growing tissues seem most affected by malnutrition.
Malnutrition delays growth. It just "slows up and waits for better times." (My comment: these events in humans imply that periods of deprivation occurred in human evolution and that growth abatement with a catchup in better times is an evolutionary adaptation.
In malnutrition, growth in size is hit harder than maturational progress. These events were extensively studied with animal studies in the 1910s and 1920s (see Krogman 135-137). Infants with severe malnutrition also has been studied. Some youth are able to catch up better than others.
(5) Psychological disturbance (See Harrison et al p 387 and section 6 in CEGD)
Emotional stress in some children inhibits hormone secretion. When the environment improves, there is catchup. Krogman (p 143) says that a child grossly neglected by its mother shows retarded growth and maturation. Such children can be under weight and even the skeletal age can be delayed. Some children are especially susceptible to stress, respond to it with under eating, and end up with an unusually short stature (CEGD pp 341-342).
The high mortality rate for infants confined to institutions has been well known for centuries. In the 1940s, 'failure to thrive' was identified in infants hospitalized for long periods. The term 'hospitalism' was thereby coined. The consequences of emotional deprivation is documented in nearly all industrialized societies, in all social classes, at all ages, but probably more often in boys than girls (CEGD p 255).
The classic study by Elsie Widdowson cited over and over is from Germany in 1948: a nasty headmistress in an orphanage caused reduced height and weight gain in children charged to her care. (Krogman 142. Bogin p 191, CEGD p 255).
Emotional development of an infant requires cuddling and maternal care. The classic studies by Harlow in the 1960s showed that monkeys raised in total isolation grew up entirely passive and were abusive when exposed to other monkeys. Females had no mothering skills. Even a 'cloth mother' afforded more benefit for the macaque infant than a 'wire mother.' (see Young, J. An Introduction to the Study of Man. Oxford: Clarendon Press, 1971 p 244)
(6) Munchausen's Syndrome / A Medical Masquerade
A few years ago, a Florida woman made national headlines: her child had 40 surgeries and 200 hospital stays. The astounding thing was that the mother had induced the illnesses! Other cases dot the literature where people have surreptitiously sabotaged their own health or that of their children.
Cases of blood dripped into a urine sample, milk injected into the bloodstream, and deliberate self mutilation are documented. One woman got chemotherapy for herself by stealing another patient's biopsy slides.
When growth--or even the services an orthodontist delivers goes awry without apparent cause, think of this one! (see Chase, M. "Munchausen's Sufferers Use Ills To Get Attention" Wall Street Journal. April 2, 1996)
(7) Socio-economic Class / Size of Family. (Bogin beginning p 148)
It is well known that children of lower socioeconomic status are generally smaller and mature less rapidly than children of higher up the scale. In developing nations such as Mexico, there are great differences in the quality of the environment for growth from rural to urban, lower to upper socioeconomic status. In England, there is a strong correlation between the growth of a child and occupation of the father.
Studies in Britain have shown that children in better-off families are taller. Well-off children mature earlier and get their teeth earlier, too. He who has gets!
In Sweden and Norway, the difference has about disappeared, probably a result of universal health care.
More intelligent children are taller than less intelligent children from the same educational background, but other subtle factors affect this difference. The author acknowledges that maybe social mobility favors larger people.
(8) Birth Order
Birth order is a curiosity. Amongst Who's Who, American Men of Science and Rhodes scholars, first borns are more frequently encountered. Harvard historian Frank Sulloway says that first borns support the status quo, are often leaders, and tend to resist revolutionary change. A high percentage of strip teasers are first born. Conservatives such as Rush Limbaugh and Calvin Coolidge are first borns.
Later borns are more open minded, are born to rebel, take risks, led the Protestant Reformation, are more likely to smoke marijuana, tend to 'buck the system' as have Karl Marx, Ralph Nader, Bill Gates and Nelson Mendela. First borns identify with parental authority; later borns often become very competitive struggling for their place. (from Stiff, D. "Blame the Birth Order for History's Revolts, This MIT Scholar Says" The Wall Street Journal. August 23, 1994.)
IV. SECULAR (GENERATIONAL) GROWTH TREND p 390. (Relethford p 451; H390, Young p 248; Baer p 44; Krogman pp 37 & 138; Bogin; CEGD pp 395-398; Mascie-Taylor and Bogin)
Children (and adults) in many Westernized countries are taller and heavier than their counterparts a century ago. There are three overall trends:
(1) An increase in height.
(2) An increase in weight.
(3) A decrease in the age at menarche (earlier puberty is seen in both boys and girls)
Secular trends are well documented in new-born babies, growing children, and adults. In adults the secular trend is seen as increased mean height, weight, head-breadth, facial with, head circumference, diameter of tooth crowns, and pelvis size.
The magnitude of this trend is considerable and it dwarfs the differences between socioeconomic classes. Secular differences in height and weight are related to changes in the rate of maturation. The children in recent times mature more quickly. The secular trend in age at menarche shows the dramatic trend toward earlier age seen in industrialized countries.
The secular growth trend is documented in many countries.
The trend has recently leveled off. Tanner dryly says that "whether or not it is good is anyone's guess." (My comment: I consider it a societal bombshell. We are in a society that worships youth and encourages sexual relations without restraint. The consequence is children are having children.
Among foraging societies, menarche was much later. Vigorous activity, disease, lower body fat and seasonal food deprivation all contributed to greatly reduced fertility.
We are seeing a gene expression previously 'silent' in leaner times. Super abundance of food is leaving us with more overweight teenagers. Many studies suggest that increased fatness, especially in the trunk of the body, leads to more type II diabetes and atherosclerotic heart disease. Will our overfed youths ultimately have shortened lives? This is just a rhetorical question. I don't know the answer.
In Native American Indians, obesity contributes to type II diabetes; however, two other factors are worth noting here because they relate to cause and effect. Maternal weight correlates highly with infant weight (Overfield p 42) Heavy birth weights in turn are associated with the increased incidence in Native American Indians (Overfield p 41)
Tanner says (p 394) that nobody knows the cause for the secular growth trend. Numerous factors have been suggested, including nutrition, reduction in childhood infectious disease, improved health care, standard of living, and reduction in family size. In general, people grow taller and complete their growth sooner when housing, clothing, food, and childhood resources are more abundant. (for a nice monograph on this topic, see Roche)
Negative secular trends have been identified recently in a small number of groups in India, Africa, and Papua New Guinea. These negative trends may be caused by environmental deterioration (CEGD p 398).
(1) Nutrition and a beneficial environment may have allowed for the expression of genetic potential latent during the industrial revolution.
(2) The social consequences are enormous. Biologically mature girls (child women if you will) in a society that constantly romanticizes sex, romantic love and do it anywhere with anyone--while they still have child minds and sit in 7th grade classrooms--with hidden estrus to boot. It all seems out of sync, at least to me.
(3) The health consequences to women with longer lives of hormonal cycles--many implicate this with breast and ovarian cancer.
(4) A rule of thumb in medical anthropology is that when people move to another culture and adopt those life ways, they will acquire many of their diseases, too. Type II diabetes and vehicular accidents are examples.
(5) Some studies suggest that the secular growth trend by require several generations for its full expression (see Mascie-Taylor and Bogin, p 70)
Are Endocrine Disruptors Real?
Are estrogen-like chemicals in the environment? According to sources cited by Constance Holden (Science (25 April 1997, p 537), 'endocrine disruptors' in some pesticides are responsible for abnormally early sexual maturation. According to a pediatric survey, 14.7% of whites and 48.3% of black youth are showing signs of pubic hair or breast budding by age eight. Stanley Garn at Michigan doubts the idea of chemicals in the environment as cause. He says what is really going on is that girls are getting steadily plumper. The issue is not settled. (see "Hormone Mimics" Consumer Reports June, 1998, Kendall, P. 'Imposter Hormones raising fears' Chicago Tribune July 14, 1997, "Pesticide-estrogen link in doubt' Chicago Tribune August 22, 1997.)
The growth consequence of precocious puberty is adult shortness. With early pubertal onset, the child component of growth is shorter than normal, thus less statural growth. (See CEDG p 111)
Environmental Toxicants and Growth
Life in industrialized society exposes people to environmental hazards never encountered in human evolution. Only a few are enumerated here.
(See CEGD pp343-345)
V. SOCIETY, CULTURE, AND GROWTH (Harrison et al p 394)
Children's growth reflects the nutritional, ecological and psychosocial aspects of their lives. The stature of vagrant boys in London and slaves in America have reflected their lives.
One of the best measures of classlessness (egalitarianism) of a society is to measure the height of its children. Such differences have largely disappeared in countries such as Sweden and Norway. (My comment: In this country, 20% of our children living in poverty; should this be considered in social policy?)
Is there evidence for a secular growth trend in teeth? Yes. (See Garn et al J. Dent. Res. 47: p 503 and CEGD) There has been a statistically significant increase in crown diameters. This is in contrast with the evolutionary reduction in the dentition and the acknowledged low correlation between body size and tooth diameters.
PHYSICAL AND PSYCHOLOGICAL DEVELOPMENT
I. CULTURAL IMPACT (Harrison et al p 396)
Studies in growth and development have social implications. They are the basis of educational theory even if that basis is implicit. Growth of the brain, critical learning periods, stages of growth and the relationship of intelligence tests to maturation are important considerations in education. (My note: children vary in their rate of development. When six-year-olds are automatically plugged into first grade, this ignores the fact that some late bloomers who are unable to cope, while early bloomers should have started earlier.)
II. GROWTH OF THE BRAIN (Harrison et al p 396)
As we saw from the Scammon curves, it developes earlier than the rest of the body; at birth it is only 25% of its adult weight.
Different parts of the brain grow at different rates (see Harrison et al for details).
Studies of World War II starvation show that the body and brain has considerable catch-up potential if post deprivation environment is good. Such conditions are often not met in developing countries.
Some old statistics suggest that boys and girls of higher intelligence grow taller.
III. EFFECTS OF THE TEMPO OF GROWTH (Harrison et al p 402)
Based on European and North American school studies, children who are slightly advanced toward maturity score slightly higher in mental ability. This is consistently true for children of all ages. Fast-maturing children have a significantly better chance than slow-maturing children.
Physically larger children score higher on IQ tests than small ones. Part of this height/IQ advantage seems to persist into adulthood. Being an early or late maturer has repercussions on behavior.
Advanced boys are often leaders; small boys are at a disadvantage in the playground. Youths tall before puberty tend to start puberty earlier than those who are short (see Tanner pp 94-104).
The author claims that early maturers are more stable, more sociable, and more successful in society.
ANALYSIS AND CLASSIFICATION OF PHYSIQUE
I. HUMAN CONSTITUTION (Harrison et al p 405)
How do people consistently differ from one another? In this study, no explicit distinction between heredity and environment is made. There are great differences in bodily form amongst humans. Different body builds have presumably certain advantages in differing circumstances and at different times. Selection may favor one build over another.
Being long and thin may be advantageous in a hot environment. Similarly, being stocky in build and having short limbs may be advantageous in an Arctic environment.
Head, cold, and relative humidity is associated with variation in the size, proportions, and composition of the human body. There is a negative correlation between body weight and mean annual temperature for a worldwide sample of populations (Bogin p 137).
As a rule, Africans in 'hot-dry' areas are taller than Africans in 'hot-wet' areas. The most extreme adaptation are the Pygmies (Bogin p 138).
Studies in Africa have shown that the warmer the climate, the lower is the body weight relative to height; under the warmest conditions the body becomes linear (see Sinclair p 138).
Two old 'rules' concerning body size and shape for polytypic species are:
(My note: we will examine these in greater detail in a future unit on adaptation.)
Physiques seems to correlate with career, delinquency, and psychiatric disturbances.
As in the case of the blood groups certain diseases select against one build more than against others; tuberculosis caused more deaths in long, thin people than in short stocky ones. There are many other examples.
The sex difference in physique is most striking: the more muscular physiques occur less often in girls than in boys.
II. THE CLASSIFICATION OF PHYSIQUE BY EXTERNAL BODY FORM (Harrison et al p 408)
The human body varies in many ways. Researchers have sought relationships between physique and such characteristics as physiological function, habitual behavior, and susceptibility to disease. Studies show that many of these variations are correlated with each other in varying degrees.
There are several systems of classification; we will only discuss the one by Sheldon.
III. SHELDON'S CLASSIFICATION OF BODY FORM/SOMATOTYPING (Harrison et al p 409; see Sinclair beginning p 133; Carter & Heath Somatotyping; Shepard Body Composition)
Aristotle, Galen, and the Arab physician Avicenna suggested a relationship between body shape, the four humors, and temperament. The Danish composer Nielson even wrote a symphony about them based on pictures he saw in a pub.
The familiar system of body form classification by Sheldon and his colleagues is known as somatotyping. It recognizes that there are no distinct types, only a continuum distributed in a Gaussian fashion. Sheldon began with nude photos of college students. (You might ask how they got the pictures. The pictures were REQUIRED in some colleges upon admission! See Carter & Heath p 11.)
Sheldon disregarded largeness or general body size; he sorted for extremes of body shape and classified them into three categories. Study of military cadets show that for each somatotype, the characteristics become more striking after maturity (see Tanner pp 94-104).
The usual age for somatotyping is at ages 20-25 years. (the following from Sinclair p 133)
There is a characteristically round; has a round head; the abdomen larger than the thorax; arms & thighs contain much fat. There is a large viscera and a good deal of subcutaneous fat. The person is thicker front to back than side to side. The extreme in endomorphy is nearly spherical.
This person is thin and narrow, with little muscle, little subcutaneous (see picture, Sinclair p 134) fat, and thin limbs. The heart lies vertically, and both his skin surface and the nervous system are relatively large. The adolescent growth spurt is about a year later than the typical mesomorph. The extreme in ectomorphy is the linear person.
The mesomorph has strong shoulders and chest, a transversely lying heart, heavily muscled limbs: the forearms and calves a stronger than the arms or thighs. The person has little subcutaneous fat; the person is thicker side to side than front to back. The extreme in mesomorphy is the classic Hercules. Muscle and bone predominate.
Most people are not such extremes. In practical application, classification is done by comparing to a standard atlas.
What is the legacy of somatotyping? (For a detailed analysis, start with Shepard and Carter & Heath.) Somatotypes are significantly related to success in physical fitness tests and in sports. Top-level athletes tend to be mesomorphic. Some somatotypes associate with certain diseases. The relationship between somatotype and temperament, behavior, personality, psychological traits are poor to moderate. Somatotype does correlate for ballet dancers. There is no correlation with religion . .
(A postscript about Sheldon from Carter and Heath, ch 1) W. H. Sheldon had a predilection for antagonizing people which hurt his career. He was an intelligent child with many interests; he earned his PhD at the U. of Chicago in 1925. To further his interests in morphology, he earned a medical degree in 1933. He traveled widely and formulated plans for a 'constitution project' all of which came to ruin in 1936.
He loved and pursued a girl that he only called 'Starlight.' When she dumped him and married another, he wrote an ill-advised and threatening letter to the new husband. The outraged recipient distributed copies of the document in the academic world; Sheldon never got an academic appointment anywhere. His subsequent research was supported by himself and loyal friends. A gifted but difficult man, he died in Cambridge in 1981 at age 76.
PHYSIQUE AND ITS RELATION TO FUNCTION, DISEASE, AND BEHAVIOR.
I. FORM AND FUNCTION (Harrison et al p 424)
Little is known about the relationships between body-build and physiological function. There are a few confirmed correlations. Systolic and diastolic blood pressure seem to be higher in broadly built persons than in linear ones. This may reflect the effect of large arm circumference producing a measurement error when using the cuff method. Blood volume relative to body weight seems higher in mesomorphy than in ectomorphs or endomorphs.
II. DISEASE (Harrison et al p 426)
Physique may relate to endocrine activity but this has not been firmly established. There is a firm link, however between certain builds being susceptible to particular diseases.
Pulmonary tuberculosis is a disease of ectomorphic builds. The physiological basis for this can only be a guess.
Coronary heart disease seems to correlate more with mesomorphic men.
Endomorphic persons seem more vulnerable to type II diabetes. Endomorphs more readily put on fat in middle age.
III. BEHAVIOR (Harrison et al p 427)
IQ seems to show little difference among the three builds. Sheldon claims that there is some relationship between body build and temperament.
IV. DRAWBACKS OF THE ERECT POSTURE (from Sinclair pp 147-149)
Do you remember how your mother and your gym teacher told you to sit up straight? That ISN'T what this section is about. It is instead a focus on the biological 'price' hominids pay for upright walking. If you have backaches, you might find this section interesting.
Erect posture frees the hands for other uses; with their manipulative ability comes increased brain size and in time, the use of tools. Further, the eyes are brought further above the ground. This is important for ground dwelling animals--whether it means seeing danger in the African savannah or being able to see the sign to the subway when on a crowded city street.
During our lives, the pull of gravity and tissue degeneration in time take their toll. It takes a complex nervous system to coordinate our precarious posture.
The vertebral column, tipped on end leads to aches and pains, degenerating joints, and vertebral disc damage. The human pelvis remains that of a four-footed animal and is an awkward compromise between running and birthing.
The postural pattern for the pregnant woman places severe strain on the vertebral column as moms with several children will testify.
The erect posture is impressive in youth, especially when viewing the agility of a trained gymnast. In old age, many of the problems of our posture emerge, including the pot belly, prolapse of the uterus and bladder, and joint disorders.
V. Senescence and Old Age (Sinclair ch 10 ; Poirier et al Ch 28; Time Frontiers of Medicine Fall, 1996 pp 76-80; Stealing Time, a PBS video and companion book. Also see CEGD pp 425-431)
A. Senescence (Sinclair p 219)
Demographically, all industrialized countries today have aging populations. It is a challenge in this country for Social Security and Medicare.
Medical science has not solved the riddle of aging. The best way to grow old is to have long-lived parents. It also helps to be female. Some claim that that males have a higher metabolic rate and therefore go through their lives more quickly. Maybe old men have less utility in society than old women. (See Gibbons, A. "Why Life after Menopause?" Science April 25, 1997 p 536)
Our health reaches its peak at age 11, at which the body has not yet begun to age. As adolescence begins, aging begins: from then on, the chance of death doubles every eight years.
One of the fastest 'oldest old' cohorts in industrialized countries at the centenarians. How do they get that old? Centarians have children late in life, they are unlikely to die of cancer. Above all they have relatives who have also reached 100. They have genes that seem to slow aging.
Our bodies have 'repair budgets.' As we get older, we 'invest' less in repair. What can we learn from the aging of other species of animals?
Size seems to matter. Birds live three times longer than mammals of the same weight. Safety and competition seem to matter, too. Some turtles live to extreme old age-in excellent health. Opossums living in cities seem to age very quickly. Their cousins living in predator-free environments on islands off South Carolina age much more slowly. (Stealing Time, a PBS special, June, 1999)
B. Aging in Cells and Tissues (Sinclair p 221)
Our two 'oldest' cell types are in the nervous system and in the musculature. We probably lose cells in the brain as we get older and muscle seems to atrophy as we get older. Many experts say that our best management is to 'use it or lose it'. Said differently, an intellectual and physically active person will do better in older life.
(See Nash, J. "Fertile Minds" Time February 3, 1997.)
One theory is the 'Hayflick' limit which says that cells can divide only a certain number of times--usually limited to the lifespan of the species. (Sinclair p 241) Telemeres at the ends of chromosomes have been implicated in aging (see Stealing Time video; I've sent for the book but it has not come as of this writing 7/15/99.)
Closely related to the Hayflick limit concept is a more general biological feature of animal cells; understood as a genetic cell death program, its execution is called aptosis. (See CEGD p 431)
Caloric restriction effectively extends life. Rats kept lean fed 40% fewer nutrients live a third longer than well-fed mice. Other experiments have confirmed these findings across the animal kingdom. Calorie restricted mice have more stamina, better control, are more active, better immune systems, and have fewer age-related diseases. Caloric restriction in monkeys results in less fat; they have much lower blood cholesterol and seem protected against diabetes. Diabetes seems to accelerate the aging process by a third.
There are human studies on the benefits of caloric restriction, but candidates to do it long term are hard to find. Interested?(see Stealing Time video)
C. Menopause (Harrison et al p 536; Gibbons, A. "Why Life After Menopause?" Science 25 Apr 97 p 536; see excellent article in CEGD pp 422-424)
Why do women have such long post-reproductive lives? Human females are the only primates to live well beyond their last pregnancy. A new study suggests that among the Hadza, a food foraging culture, grandmothers live to make sure that their grandchildren survive. It is an interesting idea and can be stated nicely as a testable hypothesis.
Among non-primates, only female killer whales and pilot whales live to experience menopause. Both species live and hunt in large groups. (Stealing Time)
A fundamental reason for menopause is that human females (like mammals in general) simply run out of eggs. None form after the fifth month IU.
D. Age and the Mind (from Stealing Time video; I'm waiting for the book!)
The elderly vary in mental faculties. The brain is unique in deciding its own destiny and what we do seems to affect our mental ability as we age.
Studies of rats show that 'cage potatoes' living in boredom have fewer dendrites than those living in 'cage Disneylands' with challenging environments changed daily. Studies of rats and humans suggest that the key to cognitive ability in old age is novelty. Intellectual enrichment, exercise, good lung function and a sense of control seem important. The best examples are conductors of symphony orchestras: Leopold Stokowski and Arturo Toscanani were active well into their eighties.
Brains do age as this writer can testify. Retention of names becomes difficult in older age. Two broad categories of brain function are described here.
Crystallized ability, the skills and knowledge acquired over a lifetime is impressive in older age. Dental instructors with skills acquired over a long career can do their chosen work very well and are comfortable working with young inquisitive students. Older typists can compete effectively with younger ones.
Fluid ability, the ability to do several tasks at once, fades as we get older. This can be tested with a 'digit symbol test' or with a demanding computer program that requires doing four tasks simultaneously. Traders on the mercantile exchange doing work that is fast paced, physically demanding, and constantly changing information is a young person's game.
Spatial orientation and inductive reasoning: dealing with landscapes and identifying patterns in our world are at the peak in our 30s and 40s, but decline after age 60. Well-educated people in good health with a flexible approach to life seem to hold up best. (Notes from Stealing Time, a PBS video.)
VI. DENTAL AND SKELETAL CHANGES OF USE TO THE PHYSICAL AND FORENSIC ANTHROPOLOGIST (Schwartz Ch 7 and Wolfe et al)
The changes in the dentition and the skeleton are well documented and are useful for the skilled forensic anthropologist in determine the age at death for skeletal remains. In childhood, the teeth are reliable and accurate means of assessing age. Anthropologists often estimate age based on the occlusal wear seen in molar teeth. For this to be reasonably accurate, all three molars should be intact and not loose from the mandible or maxillla. The population studied should have all shared the same diet.
The wear patterns on the occlusal surfaces of the teeth is useful when a fairly large population of skeletal material drawn from a single cemetery site is examined.
What skeletal characteristics can be used to judge age in adulthood? Only a few will be mentioned here.
(1) Todd's 10 Stage Pubic Symphysis Age-Related Change. (Schwartz p 200; Wolfe et al 10-42) Todd's method is used to evaluate the changes in the morphology of the pubic symphysis.
(2) Lovejoy's Staging Using the Articular Surfaces of the Left Ilia (Schwartz p 202)
Lovejoy concedes that this staging technique is somewhat more difficult than the Todd series.
(3) Iscan and Loth Age-Related Features of the Sternal end of the Rib (Schwartz p 205)
(4) Proximal Femur Aging (see Sinclair)
Lipping is a change that begins at about 35 to 40 years of age. It is found in the vertebrae in the back and the long bones in the arms and legs develop ridges or lips at their edges. It is a natural arthritic maturational event, a normal aging phenomenon. In old age it can become extreme and will even fuse joints. (Baer p 60)
(5) Suture Closure in the Skull (Wolfe et al p 10-38)
After the age of seventeen, the sutures of the skull begin to fuse, until in very old age, the sutures are completely obliterated. The fusing or ossification of the sutures begins on the inside of the skull and proceeds to the outside of the skull. The age at which sutures fuse has been documented; however, the aging must be done with caution.
SUTURE CLOSURE OF THE CRANIUM
A. Midcoronal = by age 40 years
B. Sphenofrontal = by 65 years
C. Pterion = by 72 years of age
D. Temporoparietal = by 80 years of age
E. Sagittal = by 40 years of age
F. Lamdoidal = by 50 years of age
G. Temporooccipital = by 80 years of age
H. Sphenotemporal = by 65 years of age
..... CJ '99
Resources (see also book list in CEGD p 487)
Baer, Growth and Maturation. Cambridge: Doyle Publishing Company, 1973.
Bogin, B. Patterns of Human Growth. New York: Cambridge University Press, 1993.
Bunney, S. ed. Cambridge Encyclopedia of Human Evolution. Cambridge: Cambridge University Press, 1994.
Carter, J. and Heath, B. Somatotyping-Development and Applications New York: Cambridge University Press, 1990.
Harrison, G., Tanner, J., Pilbeam, D., and Baker, P. Human Biology 3rd ed. New York: Cambridge University Press, 1993.
Krogman, W. Child Growth. Ann Arbor: University of Michigan Press, 1972.
Mascie-Taylor, V. and Bogin, B. Human Variability and Plasticity. New York: Cambridge University Press, 1995.
Overfield, T. Biologic Variation in Health and Illness. Boca Raton: CRC Press, 1995.
Poirier, F., Stini, W., and Wreden, K. In Search of Ourselves 5th ed. Prentice Hall: Englewood Cliffs, 1994.
Roche, A. ed. Secular Trends in Human Growth, Maturation, and Development. Chicago: The University of Chicago Press, 1979.
Schwartz, J. Skeletal Keys. New York: Oxford University Press, 1995.
Mascie-Taylor, C. and Bogin, B. Human Variability and Plasticity New York: Cambridge University Press, 1995.
Shepard, R. Body Composition in Biological Anthropology New York: Cambridge University Press, 1991
Sinclair, D. Human Growth after Birth. New York: Oxford University Press,
Tanner, J. Growth at Adolescence, 2nd ed. Oxford: Blackwell Scientific Publishing, 1962.
Tanner, J. "Human Growth and Constitution" in Harrison, G. et al Human Biology, 3rd ed. New York: Oxford University Press, 1993.
Ulijaszek, S. et al eds Cambridge Encyclopedia of Human Growth and Development New York: Cambridge University Press, 1998.
Wolfe, L., Lieberman, L., and Hutchinson, D. Physical Anthropology Laboratory Textbook, 4th ed. Raleigh: Contemporary Publishing Co., 1994.)