Chapter 5
How many races did Blumenbach conclude existed?
Five: Mongoloids, Malays, Ethiopians (Africans), American Indians, and Caucasoids. These types were static—they did not change over time.
The American anthropologists Nina Jablonski and George Chaplin have shown that the best predictor of skin color, as measured by skin reflectance, is ____________ ___________. That is, the darkest skin (low skin reflectance) is associated with the highest , and the lightest skin (high skin reflectance) is associated with the lowest.
UV radiation exposure
rickets
found in infants due to a lack of vitamin d resulting in softening of bones.
Genetic adaptation
Occurs at the population level via natural selection. Here, the biological change is inherited and is not reversible in a person (e.g., someone with sickle-cell anemia).
________________, the loss of ovarian function, is a key element of female senescence, marking the end of the reproductive phase and the end of childbearing.
Menopause
Dark-skinned people have a sun protection factor (SPF) of _________; light-skinned people have an SPF of between ________.
10-15, 2-3 Around the world, populations with the most melanin have the fewest skin cancers and malignant melanomas. However, these effects occur largely during or after the late reproductive years, suggesting that skin cancer is not an element of natural selection.
Cline
A gradual change in some phenotypic characteristic from one population to the next.
cline
A gradual change in some phenotypic characteristic from one population to the next.
secular trend
A phenotypic change over time, due to multiple factors; such trends can be positive (e.g., increased height) or negative (e.g., decreased height).
deciduous dentition
Also known as baby teeth or milk teeth, this is the first set of teeth, which forms in utero and erupts shortly after birth.
Like all other mammals, humans are homeothermic, meaning they:
maintain a constant body temperature.
_________ is a natural sunscreen, individuals with high levels of it receive the most protection.
melanin
Support for the evolution of skin pigmentation in humans is provided by the fundamental role of melanin in the protection of stored __________ in our bodies. New research shows that it is essential for the synthesis and repair of DNA, and just a very tiny deficiency can be linked to a range of health issues.
folate (folic acid)
Each of the five postnatal periods has a different _______ velocity
growth
What are some secondary stresses to being in high altitudes?
high UV radiation, cold, wind, nutritional deprivation, and the rigors of living in highly variable, generally rugged terrain.
The American physical anthropologist C. Loring Brace has argued that the race concept got its start in the
in the fourteenth century during the Renaissance.
During the __________ years, growth slows. Although much learning occurs in childhood, the full-size brain makes possible formalized education and social learning.
juvenile
During childhood, general growth ________ off but the still rapidly growing brain requires the child to have a diet rich in _________, _________, and energy.
levels, fats, protein
Humans adapt to cold, but how do adaptations include cultural and behavioral factors?
people teach their children how to avoid situations involving heat loss.
Humans are also the only primates that experience, at the other end of the life history, prolonged _________________ survival.
postmenopausal Some apes have a postmenopausal period, but it is briefer than humans'. Ethnographic evidence from cultures around the world shows that postmenopausal women, most often grandmothers, play important roles in caring for children, provisioning food to children, and providing essential information about the world to various members of their social groups
Three stages of growth cycle
prenatal, postnatal, adult
True or False? Our cells are replaced every seven years
False.
True or False? Functional adaptations can never be replaced by equivalent genetic adaptations.
False. Functional adaptations are not turned into genetic adaptations. However, the same conditions that result in a developmental or physiological adaptation may also result in natural selection for a trait that addresses the same, or a similar, environmental problem.
True or False? Most vitamin D obtained through diet.
False. Most vitamin D is produced in the skin
What finding undermined the idea that racial types were innately stable.
In the early 1900s, Boas and his researchers studied some 18,000 immigrant families, calculating the cephalic index—the ratio of head length to head breadth—of parents born in Europe and their children born in the United States. Their results revealed that the adults' and children's head shapes differed, not by a lot but by a degree that could be expressed mathematically. Because the differences that had been cited among various races were not immutable, Boas concluded, the race concept was invalid. Boas's work laid the foundation for a scientific focus on biological process rather than on typological classification.
melanocytes
Melanin-producing cells located in the skin's epidermis.
______________ such as walking and running develop during the first two years. ___________ abilities also progress rapidly during this time, reflecting the very rapid growth and development of the brain during infancy
Motor skills, Cognitive
Without vitamin D, the bones do not mineralize properly, resulting in a condition called _______ in children and ________ in adults
rickets, osteomalacia
Acclimatization (or physiological adaptation)
Occurs at the individual level, but unlike developmental adaptation, it can occur anytime during a person's life. In this kind of adaptation, the change is not inherited and can be reversed. For example, exposure to sunlight for extended periods of time results in tanning (also discussed further below, see "Solar Radiation and Skin Color").
By about age ______, permanent teeth begin to replace primary teeth, and ______ growth is completed
six, brain
One of the most profound environmental factors that humans deal with daily is ____________ ___________, or the sun's energy output, which plays a central role in the evolution and development of skin color
solar radiation
Allen's rule
states that heat-adapted mammal populations will have long limbs, which maximize the body's surface area and thus promote heat dissipation, whereas cold-adapted mammal populations will have short limbs, which minimize the body's surface area and thus promote heat conservation.
Bergmann's rule
states that heat-adapted mammal populations will have smaller bodies than will cold-adapted mammal populations. Relative to body volume, small bodies have more surface area, facilitating more rapid heat dissipation. Conversely, large bodies have less surface area, thus conserving heat in cold climates
Developmental (or ontogenetic) adaptation
Occurs at the level of the individual during a critical period of growth and development, childhood especially. The capacity to make the change is inherited, but the change is not inherited and is not reversible. For example, children living at high altitudes develop greater chest size prior to reaching adulthood than do children living at low altitudes. The expanded chest reflects the need for increased lung capacity in settings where less oxygen is available (discussed further below, see "High Altitude and Access to Oxygen").
If race is not a valid way to account for human diversity, how do we speak meaningfully about the enormous range of variation in all kinds of human characteristics around the globe?
One important finding from physical anthropologists' study of human variation is that specific biological traits generally follow a geographic continuum, also called a cline.
Is race a valid, biologically meaningful concept?
Race is a typological leftover from pre-evolutionary, taxonomic interpretations of biological variation. Race is neither a useful nor an appropriate biological concept. • Human variation is clinal. In general, traits (skin color, cranial form, and genetic polymorphisms) do not correlate in their distribution. There would have to be a concordance of traits for races to exist.
homeothermic
Refers to an organism's ability to maintain a constant body temperature despite great variations in environmental temperature.
motor skills
Refers to the performance of complex movements and actions that require the control of nerves and muscles.
Microsatellites
Repeated segments of DNA that are so different from person to person that they have become an important tool in the identification of humans—living and deceased—in forensic, archaeological, and other contexts (see chapter 3, "Polymorphisms: Variations in Specific Genes").
_______________, which accompanies aging, is a biological process characterized by a reduction in ________________, the body's ability to keep its organs and its physiological systems stable in the face of environmental stress.
Senescence, homeostasis
Melanin, the primary influence on vitamin D synthesis, can be advantageous or nonadvantageous. How is this?
Simply, skin needs to be dark enough to protect from UV radiation but light enough to allow solar radiation sufficient for vitamin D production.
homeostasis
The maintenance of the internal environment of an organism within an acceptable range. the body's ability to keep its organs and its physiological systems stable in the face of environmental stress.
weaning
The process of substituting other foods for the milk produced by the mother.
basal metabolic rate (BMR)
The rate at which an organism's body, while at rest, expends energy to maintain basic bodily functions; measured by the amount of heat given off per kilogram of body weight.
When did ehe early scientific articulation of the race concept—namely, that living humans could be lumped into different taxonomic groups emerge?
the eighteenth century. By the 1700s, Europeans had encountered most of the biological diversity of the world's populations. Johann Friedrich Blumenbach (1752-1840) developed a biological taxonomy of human races. Blumenbach based his taxonomy on human skin color and other physical traits but mainly on features of the skull, such as the facial projection.
What happens once the epiphyses have fused to the diaphyses?
the growth in length stops and the individual's height is set
What is internal heat produced by?
the metabolism. especially during activities involving movement, such as physical labor, walking, and running.
In daylight, skin is exposed to _______ _________, a component of solar radiation.
ultraviolet (UV) radiation
Like most cold-adapted populations, however, the Inuit have adapted physiologically by developing a capacity for tolerating excessive cold. For example.....
Their peripheral body temperatures, in the hands and feet, are higher than other peoples' because of a higher rate of blood flow from the body's core to the skin. The Inuit also conform to Bergmann's and Allen's rules, having large, wide bodies and short limbs. Moreover, they have developed a technology that conserves heat: their traditional housing focuses on insulation
True or False? bone loss is a senescence universal.
True. That is, after age 40 humans suffer increased bone porosity and reduction in bone mass. The increased susceptibility to bone fracture that comes with this loss is called osteoporosis. In extreme cases, osteoporosis can weaken bone to the point that it easily fractures under small amounts of stress.
Are there exceptions to Bergmann's and Allen's rule?
Yes, but by and large these rules explain variation in human shapes that goes back at least 1.5 million years.
hypothermia
A condition in which an organism's body temperature falls below the normal range, which may lead to the loss of proper body functions and, eventually, death.
Humans can tolerate a body temperature higher than their normal _____ °F, but a body temperature above ___-___ °F for an extended period leads to organ failure and eventually death.
98.6, 104-107
functional adaptations
Biological changes that occur during an individual's lifetime, increasing the individual's fitness in the given environment.
_____ and ______ growth rates are higher than _____ and ______ ________ growth rates.
Brain, dentition, body, reproductive system.
The biological benefits of physical activity are clear:
Exercise improves physical fitness by contributing to bone strength, helping lower blood pressure and cholesterol, increasing heart function and lung function, and so on. Exercise that becomes an excessive workload, however, can hinder female reproductive function, a
Most functional adaptations are associated with
Extreme environmental conditions, such as heat, cold, high altitude, and heavy workload. Some of these conditions appear to have brought about genetic changes in humans. That is, over hundreds of generations humans have adapted to settings in which specific attributes enhance the potential for survival and reproduction. Skin pigmentation, for example, is related genetically to solar radiation exposure.
cultural (or behavioral) adaptation
Involves the use of material culture to make living possible in certain settings. For example, wearing insulated clothing keeps people from freezing in extreme cold.
The American economic historians Dora Costa and Richard Steckel have shown that between 1710 and 1970 substantial changes occurred in the heights of American males of European descent. Initially, a gradual increase in heights likely reflected improved living conditions and food availability. The sharp decline in heights around 1830 coincided with the ___________ trend.
urbanization As people moved from rural, agricultural settings to overly crowded cities, they were exposed to more diseases that were easily passed from person to person. In addition, high population densities caused great accumulations of garbage and waste, which may have polluted water supplies and thus exposed people to more bacteria, viruses, and parasites that caused infection and disease. As living conditions improved at the beginning of the twentieth century, as trash removal became mandatory and sewers were constructed, height increased. Today, Americans' heights are among the greatest in the country's history, thanks to reliable food supplies, unpolluted water, and access to medical care.
Whereas the previous life stages are generally predictable in their timing (mostly due to genetic programming), the chronology of senescence is highly __________.
variable.
The human body's first response to cold stress is _______________, the constriction of the blood vessels beneath the skin. Decreasing the diameter
vasoconstriction
The body needs UV radiation for the synthesis of _______ __
vitamin D
How do people adapt to environmental extremes and other circumstances?
• Humans are remarkably responsive to their surrounding environments. Some adaptations to the environment are genetic (e.g., skin color), whereas others occur within the individual's lifetime and either have a genetic basis and are irreversible (e.g., lung volume in high altitude) or have a genetic basis and are reversible (e.g., skin tanning). Biological change associated with all forms of adaptation occurs to maintain homeostasis. • Most functional adaptations—adaptations that occur during the individual's lifetime—have important implications for evolution, such as selection for darker skin near the equator and for lighter skin in northern latitudes. • Skin color (pigmentation) is subject to forces of evolution. Evolution of skin color is strongly influenced by environmental circumstances, especially by the amount of UV radiation. UV radiation is the catalyst for the skin's synthesis of vitamin D. Light skin evolved in areas with reduced UV radiation. • Adaptation in high altitudes where less oxygen is available includes increased lung volume and a circulatory system that more efficiently transports oxygen throughout the body. Some differences between high-altitude populations and other populations may be evolutionary (genetic), such as high oxygen saturation in the high-altitude populations. • Undernutrition is not the result of adaptation—the body either receives adequate nutrition and access to energy (calories) and nutrients or it is deficient in these resources. Nutritional deficiencies promote growth disruption, disease, and reduced fertility. Much of the human population globally is deficient in energy, nutrients, or both. In developed and underdeveloped nations around the world, obesity is a growing health threat, and associated health problems include high blood pressure, type 2 diabetes, osteoarthritis, various cancers, and heart disease. page page 130 • The key element of workload adaptation is skeletal function and maintenance of bone strength. Strength of bone and its ability to support the body are determined by the density and distribution of bone tissue in cross section. • High levels of physical activity have a negative effect on women's reproductive potential.
Molar Eruption and Brain Development
(a) Permanent teeth form during the early years of life and begin to erupt around age six. In this X-ray image, the first permanent molars, called the six-year molars, have erupted. The second permanent molars, the 12-year molars, are still forming and will not erupt for another six years. The crowded anterior dentition, or front teeth, includes the deciduous teeth and new permanent teeth waiting to erupt and take their places. (b) Brain growth and development finish at around the same time as the full eruption of the first permanent molar.
Long Bone Growth
(a) This magnetic resonance image (MRI) of a child's knee shows the joining of the femur, or upper leg bone, with the tibia, or lower leg bone. Long bones like these begin as three separate bones—the diaphysis, or shaft, and two epiphyses, or ends—separated by a growth plate. (b) In this photo of a child's knee joint, the epiphyses have not yet fused to the diaphysis. The line of union may be visible for several years after the attachment occurs; when it eventually disappears, the bone appears as a single element.
As a human biological universal, menopause usually occurs by age _____, but it varies by several years in different populations.
50
Indigenous people living in cold settings, such as the Indians at high altitudes in the Peruvian Andes, have a significantly higher ______________ than do other human populations.
BMR
______________ the diameter of the blood vessels reduces blood flow and heat loss, from the body's core to the skin. The chief mechanism for producing heat is _____________.
Decreasing, shivering
True or False? Homeothermy is a feature in almost all animals.
False. Homeothermy is a feature of mammals, but not reptiles. Reptiles use the external environment to set their internal body temperature. They have slow metabolisms. Mammals create their internal heat within their own bodies as they digest their food using their fast metabolisms.
True or False? Human populations who have lived in hot climates for most of their history—such as native equatorial Africans and South Americans—have more sweat glands as other populations.
False. They have the same number of sweat glands as other populations. However, heat-adapted populations sweat less and perform their jobs and other physical functions better in conditions involving excessive heat than do non-heat-adapted populations.
How does UV radiation affect folate levels?
Folate levels decline dramatically with exposure to high and prolonged levels of UV radiation. However, skin color and melanin production are key elements in protecting the body from folate depletion. Thus, natural selection would have played a key role in maintaining relatively dark skin in regions of the world with high UV-radiation exposure.
__________, the founder of American anthropology, was among the first scientists to challenge the taxonomic approach to human biological variation. Specifically, he wanted to test the widely held notion that head shape and other so-called racial markers were _______ entities, essentially unchanging through time.
Franz Boas, static
Humans adjust remarkably well to new conditions and to challenges. As in other organisms, such adaptations—functional responses within particular environmental contexts—occur at four different levels:
Genetic adaptation Developmental (or ontogenetic) adaptation Acclimatization (or physiological adaptation) cultural (or behavioral) adaptation
Single biological traits, such as cranial shape, had seemed like such a firm basis for racial categories in part because it is so easy to classify when focusing on just one characteristic. What happens when human populations are grouped according to multiple characteristics?
In the early 1970s, the American geneticist R. C. Lewontin (b. 1929) tested the race concept by studying global genetic variation. If human races existed, most genetic diversity would be accounted for by them. Focusing on blood groups, serum proteins, and red blood cell enzyme variants, Lewontin found that the so-called races accounted for only about 5%-10% of the genetic diversity. In other words, most variation occurred across human populations regardless of "racial" makeup—human "races" have no taxonomic significance. Since Lewontin's study, many other genetic studies have reached the same conclusion.
How does human body growth differ from in wealthy and non-wealthy countries?
In wealthy nations, the increase in height has come to a stop or slowed considerably, most likely because growth has reached its genetic limit. In many less wealthy (and thus less healthy) nations, growth potential has not been reached and growth periods are comparatively slow.
When first exposed to UV radiation, what happens to light skin?
It reddens—the process commonly called sunburn. With ongoing exposure, the melanocytes increase the number and size of melanin granules. In addition, the outer layer of the epidermis thickens.
hypoxia
Less than usual sea-level amount of oxygen in the air or in the body.
How does male senescence differ from female senescence?
Men normally produce sperm well into their 70s and 80s. However, the number of well-formed sperm and their motility decline by half after age 70.
Osteoporosis
Osteoporosis (a) As this graph shows, men and women reach their maximum bone mass around age 30. (b) The loss of bone mass becomes evident in the grayish areas of X-rays (arrows). Notice the porous pelvic bones, which with normal bone mass would be solid white.
After being exposed to survivable cold for more than a few days, humans shiver less, produce more heat, and have higher skin temperatures. Meaning.....
Overall, adjusting to cold means becoming able to tolerate lower temperatures—simply, feeling better in the cold.
senescence
Refers to an organism's biological changes in later adulthood. Senescing persons are increasingly susceptible to stress and death and have a decreased capacity to reproduce.
cognitive abilities
Refers to the capacity of the brain to perceive, process, and judge information from the surrounding environment.
What is another response to elevated temperature?
Sweating Sweat is mostly water produced by the eccrine glands, which are located over the entire body's surface. Evaporation of the thin layer of water on the skin results in cooling of the surface. Humans can sweat a remarkably high volume of water, and this physiological process is central to humans' long-term functional adaptation to heat.
How does the body adapt to higher altitudes?
The body begins to more efficiently use reduced amounts of oxygen in the air and homeostasis is restored. Extra red blood cells and oxygen-saturated hemoglobin are produced. The hemoglobin transports oxygen to body tissues, while an expansion in the diameter of arteries and of veins allows increased blood flow and increased access to oxygen.
personal genomics
The branch of genomics focused on sequencing individual genomes.
vasoconstriction
The decrease in blood vessels' diameter due to the action of a nerve or of a drug; it can also occur in response to cold temperatures.
epiphyses
The end portions of long bones; once they fuse to the diaphyses, the bones stop growing longer.
Humans have a strong capacity to adapt to excessive heat, demonstrated by:
The fact that individuals who have not often experienced such heat are less able to conduct heat away from their cores and less able to sweat than are individuals living in hot climates. Individuals exposed for the first time to a hot climate, however, rapidly adjust over a period of 10-14 days. This adjustment involves a lowering of the body's core temperature, a lowering of the threshold for when vasodilation and sweating begin, and a reduction of the heart rate and metabolic rate.
prenatal stage
The first stage of life, beginning with the zygote in utero, terminating with birth, and involving multiple mitotic events and the differentiation of the body into the appropriate segments and regions.
Changes in Height Beginning in the 1700s
The heights of soldiers, students, and slaves were routinely collected for identification or registration purposes. By combining these data with subsequent figures, Costa and Steckel discovered patterns of increase and decline in the heights of American-born males of European descent. From about 171.5 cm (67.5 in) in the early 1700s, heights rose to about 174 cm (68.5 in) around 1830, then sharply declined by 5.1 cm (2 in) over the next 70 years. After the late 1800s, heights increased by a few centimeters or a couple of inches per year throughout the twentieth century. Simply, the extraordinarily poor sanitation and health conditions in nineteenth-century cities resulted in increased disease, stress, and attenuated growth. The subsequent increase in Americans' heights reflected improvements in sanitation, nutrition, and health.
vasodilation
The increase in blood vessels' diameter due to the action of a nerve or of a drug; it can also occur in response to hot temperatures.
diaphyses
The main midsection, or shaft, portions of long bones; each contains a medullary cavity.
sun protection factor (SPF)
The rating calculated by comparing the length of time needed for protected skin to burn to the length of time needed for unprotected skin to burn.
postnatal stage
The second stage of life, beginning with birth, terminating with the shift to the adult stage, and involving substantial increases in height, weight, and brain growth and development.
growth velocity
The speed with which an organism grows in size, often measured as the amount of growth per year.
adult stage
The third stage of life, involving the reproductive years and senescence.
What trimester culminates in birth, the profoundly stressful transition from the intrauterine environment to the external environment?
Third Half of all neonatal deaths occur during the first 24 hours. Most of these deaths are caused by low birth weight. Because individuals of low socioeconomic status tend to be exposed to environmental stresses, their children are prone to low birth weights and early deaths. And a poor intrauterine environment predisposes the person to developing specific diseases later in life.
Growth Curves of Body Tissues
This chart shows the varying growth curves of the brain, body, dentition, and reproductive system in humans. The brain grows the fastest, reaching full cognitive development around age six. In fact, humans have such a large brain that much of it needs to be attained after birth; if the brain reached full size before birth, women would not be able to pass newborns' heads through their pelvic regions. Dentition has the next highest growth velocity (see Figures 5.3 and 5.5). The body grows more slowly and continues until as late as 24 or 25 years of age. The reproductive system does not begin substantial growth and development until the onset of puberty, but it reaches completion around age 15-16 for girls.
True or False? The idea of race—that human variation can be classified—is a recent invention.
True Early written records do not employ the concept. For example, even though ancient Egyptians represented sub-Saharan Africans in their art, they never referred to the Africans' race. The Greek historian Herodotus (ca. 484-ca. 420 BC) traveled widely but never wrote about race. Similarly, the great Venetian historian and traveler Marco Polo (1254-1324), who saw more of the known world than anyone else of his day, recorded huge amounts of information about his sojourns in Asia without mentioning race.
True or False? Children with less bone mass due to habitual physical inactivity become predisposed, as adults, to osteoporosis and fracture.
True. Similarly, in one study of military recruits' leg bones, young men and women who had better-developed muscles and greater bone mass were less susceptible to fractures than were young men and women who had less-developed muscles and less bone mass.
True or False? When a period of growth disruption occurs before adulthood, the resulting height deficit can be made up through rapid growth.
True. In one long-term study, of the Turkana in Kenya, growth has been documented to continue into early adulthood. Turkana children tend to be shorter than American children. However, the Turkana's growth extends well into their 20s, and Turkana adults are as tall as American adults. Few long-term growth studies have been done of nutritionally stressed populations, so we do not know about many other settings in which growth extends into adulthood. By and large, in areas of the world experiencing nutritional stress, adults are short owing to lifelong nutritional deprivation.
True or False? Far more common in women than in men, osteoporosis shows less age variation than menopause does.
True—because a loss of the hormone estrogen is linked to bone loss. Other factors that can predispose people to this condition are smoking, chronic diseases, and some medications.
What is the initial physiological response to an elevated temperature?
Vasodilation, the dilation (expansion) of the blood vessels near the body's surface. By increasing blood vessels' diameter, the body is able to move more blood (and associated heat) away from the body's core to the body's surface. The red face of a person who is in a hot environment is the visible expression of vasodilation.
What do anthropologists use to measure heat production?
a specific kind of measurement called the basal metabolic rate (BMR).
Two behaviors make possible the survival and adaptive success of humans and other primates:
acquisition of food and reproduction. Unlike the other primates, humans acquire food and reproduce within the contexts of culture and society. For example, humans have created social institutions—especially kinship and marriage—and beliefs and rules supporting these institutions. Anthropologists are keenly interested in the relations between humans' sociocultural behaviors and the evolution of our unique life history, especially in comparison with other primates' life histories.
The long-term association between body shape and climate means that body shape is mostly a genetic adaptation. However...
body shape also involves childhood developmental processes that respond to climatic and other stressors, such as poor nutrition. For example, poor nutrition during early childhood can retard limb growth, especially of the forearm and lower leg, resulting in shorter arms and legs. Ultimately, then, body shape and morphology reflect evolutionary and developmental processes.
This twentieth-century trend of increasing tallness, sometimes called a secular trend, has been noted in many other countries as well. Multiple factors have contributed to particular causes from place to place, but the collective increase in stature has resulted from improvements in ________ control and _________.
disease, nutrition
While bone growth and epiphyseal fusion are influenced by genes and sex hormones, the amount of growth and the terminal length of bones are strongly affected by ____________.
environment Especially by nutrition and general health.
Prior to the completion of growth, the ends of the long bones—the humerus, radius, and ulna in the arm and the femur, tibia, and fibula in the leg—are separate growth centers called __________.
epiphyses
What is the single strongest factor in determining skin pigmentation?
exposure to ultraviolet radiation
Because growth and development are at their most dynamic during the ____ trimester, the embryo is highly susceptible to disruption and disease caused by mutation or environmental factors. Specific stressors, or potentially harmful agents, include the mother's smoking, consuming alcohol, taking drugs, and providing inadequate nutrition
first
Unlike other primates, humans experience increased ______ ________ during adolescence.
growth velocity When nutrition is adequate and stressors are minimal, the adolescent growth spurt can add as much as 8.9 cm (3.5 in) to boys and somewhat less than 7.6 cm (3 in) to girls. Boys complete their growth later than girls, whose growth spurts peak earlier than boys'. Growth spurts either do not happen or are minimized in very highly stressed populations, such as the Quechua Indians, who live in high altitudes of Peru and suffer from cold, overwork, malnutrition, and hypoxia (a condition discussed below, see "High Altitude and Access to Oxygen").
At high altitudes, a fall in barometric pressure reduces oxygen molecules. The primary environmental stress in such places is ________, the condition in which body tissues receive insufficient amounts of oxygen
hypoxia
Overall, women are _____ able to tolerate heat than are men.
less. In part due to a relatively reduced ability to move blood to the skin through vasodilation and the presence of greater body fat.
While Blumenbach had focused on skulls, his racial taxonomy was subsequently applied to the _______ populations represented by those skulls.
living
All adaptations have one purpose: _______________ of ______________ ____________, or maintenance of the normal functioning of all organs and physiological systems.
maintenance of internal homeostasis The maintenance of homeostasis involves all levels of any organism's biology, from biochemical pathways to cells, tissues, organs, and ultimately the entire organism.
The growth and development of _______, prenatally and postnatally, are more sensitive to environmental insult than are the growth and development of _______.
males, females Human biologists have found much evidence of these differences in developing countries, but they have not been able to explain the mechanisms at work. In terms of evolution, it would make sense for females to have developed buffers from stress because females' roles in reproduction, including pregnancy and lactation, are much more demanding than males'.
Humans have a relatively prolonged childhood. However, within this life period the spans of infancy and lactation are quite short. The mother's brief intensive child care allows her, theoretically, to have:
more births and to invest her resources among all her children.
highly physically active human populations—those that do lots of walking, lifting, carrying, or anything else that "stresses" the skeleton—have bones with __________.
optimum density
Biologically, adulthood is signaled by the completion of _________, the reaching of ________, and the fusion of the __________.
sexual maturity, full height, epiphyses
Sweating is less effective in areas of the body having a dense hair cover than in areas of the body having little or no hair. What does this relationship suggest?
that sweating evolved as a thermoregulatory adaptation in association with the general loss of body hair. Humans' loss of body hair is unique among the primates, indicating that the thermoregulatory adaptation of hair loss and sweating occurred in human evolution only.
What do growth and development tell us about human variation? What are the benefits of our life history pattern?
• Differentiation and development of all the body organs occur during the prenatal stage of life. Environmental stress during this stage predisposes the individual to disease later in adulthood. • The postnatal stage—from infancy to childhood to the juvenile period to adolescence to adulthood—involves growth acceleration and deceleration. Childhood and adolescence are long events, in which adult behaviors are learned, individuals become completely mature, and the reproductive capacity develops. • Old age and senescence have long been ignored as important life stages. The length of the period is unique to humans. Individuals older than 50 play important roles in the care of young, in food provisioning for the young, and as sources of information for other members of their kin groups and societies.