Human adaptation and acclimatization

Adaptations – response to environmental conditions by adjustments of physiological processes or behavior to I prove an organism’s change of survival. To be a true “adaptation” the adjustment must be genetic, even if partially influenced by the environment. It should represent a population’s response.

Acclimatization – short term (functional) adjustments to the environment.

Quotes from Darwin Descent of Man Chapter 2:

When we compare the differences in stature between the Polynesian chiefs and the lower orders within the same islands, or between the inhabitants of the fertile volcanic and low barren coral islands of the same ocean,*(2) or again between the Fuegians on the eastern and western shores of their country, where the means of subsistence are very different, it is scarcely possible to avoid the conclusion that better food and greater comfort do influence stature.

Height in a population can change with nutrition.

Figure 5.11 Height and Economically Disadvantaged PopulationsOur Origins, 2th Edition

Copyright © 2011 W.W. Norton & Company

v

Human Growth and Development is influenced by

Hormones – chemical messengers that regulate biological processes in different tissues. hypothalmus – regulates homone secretion,

pituitary gland – secretes hormones into blood stream endocrine glands – produce additional hormones

Thyroxine – produced by thyroid gland. Increases Oxygen consumption in different body tissues, thereby regulating metabolic rate.

Growth Hormone – secreted by pituitary, vital for normal postnatal growth and maturation. Increases protein synthesis and rate of cell multiplication. To work properly an individual must be well-nourished and have a proper amount of thyroxine.

Sex hormones – affect the timing and pattern of growth. Androgens (esp. testosterone) stimulate the secondary sexual characteristics. They also stimulate growth and maturation of bone and enhance muscle growth in males. Estrogens – stimulate the development of secondary sexual characteristics in females and influence the accumulation of fat tissues.

Adrenal glands – produce adrenal hormones which are a secondary source of sex hormones.

Adrenarche – increased secretion of adrenal hormones during mid childhood at about 7 years of age, is responsible in age and human differences in the ratio of upper to lower body length and mid-facial growth.

Nutrition – places limitations on growth and development

Too little nutrient energy can result in a reduction of overall size and delayed maturation. Too much results in accumulation of fat and sometimes too early maturation. Foods must provide essential amino acids, most of which come from meat, eggs, fish and milk.

Malnutrition involves both the amount and types of foods eaten. Where it is chronic, height is reduced at every age along the growth curve and full potential adult height is never reaches, although the total growth span is prolonged to 25-26 years (as opposed to 18-21 years) to compensate.

Reduced growth and reduced body size may be an adaptation to decreased nutrients in the environment since a smaller person needs fewer nutrients.

Darwin:

Dr. Beddoe further believesthat wherever a "race attains its maximum of physical development,it rises highest in energy and moral vigour."*(The Quechua Indians inhabit the lofty plateaux of Peru; and Alcide d'Orbigny states* that, from continually breathing a highly rarefied atmosphere, they have acquired chests and lungs of extraordinary dimensions. The cells, also, of the lungs are larger and more numerousthan in Europeans. These observations have been doubted, but Mr. D. Forbes carefully measured many Aymaras, an allied race, living at the height of between 10,000 and 15,000 feet; and he informs me*(2)that they differ conspicuously from the men of all other races seen bykkhim in the circumference and length of their bodies. These men are so thoroughly acclimatised to their cold and lofty abode, that when formerly carried down by Spaniards to the low

easternplains, and when now tempted down by high wages to thegold-washings, they suffer a frightful rate of mortality.

Secular trends in height are correlated to trends toward an earlier onset of puberty.

Two critical brain growth spurts – 6-8 fetal months of age and 6-8 postnatal months.

If malnutrition occurs during critical periods of vulnerability to the brain, the damage may be permanent. After the critical period, the effects are reversible. Children in Mexico did not recover, those in Jamaica, Uganda and Nigeria did. If body growth is retarded at the time of brain growth spurt, there is a disproportionate reduction of the cerebellum and neuron cells, reading to a reduction in subsequent nutritional rehabilitations.

Children who died of malnutrition during he first year of life have reduced brain weight and size.

Kwashiorkor – severe deficiency in protein, but not in calories. During the first year, growth in height and weight is reduced by 60-80% of the expected standard. Children will have skin problems, edema, depigmentation of skin and hair, hair may fall out. The child will be listless and irritable.

Marasmus – severe deficiency in protein, but not in calories. Results in chronic, symmetrical reduction of all nutrients, approaching starvation level. It causes drastic reduction in growth and development. The child exhibits extreme muscular waisting, and a near lack of subcutaneous fat.

50% of Guatemalan children were born with high immunoglobulin (IgM) levels when compared to disease and die more quickly from them.

Malnourished children are more susceptible to Infections cause reduced food intake, increased losses of vitamin C, iron, and nitrogen in urination. Because requirements for protein and other nutrients are higher during infections, infection makes malnutrition worse.

Malnutrition decreases immunoglobulins (Ig A) in nasopharyngeal salivary secretions, such as mucose, tears and saliva. This low production facilitates colonization of the mucose surce by microorganisms and predisposes the children to infection.

Malnutrition does not affect the capacity to produce antibodies therefore malnourished kids have high immunoglobines.

Malnourished children have smaller lymphocyte glands (Thymus, lymph, and tonsils). THis depressed cellular immunodeficiency contributes to a marked susceptibiligy of malnourished children to infections (TB, herpes, etc..)

Growth and Chronic Undernutrition

Prenatal growth is retarded if protein is too little in diet.

More Low Birth Weight Babies and more preemies are born in rural.Mexico. Large calorie supplements given to pregnant mothers improved birth weight.

Women who migrated to Mexico City from rural areas during childhood had larger newborns than women who migrated there after puberty. Therefore there is a delayed intergenerational effect.

Children experienced low and prolonged growth and later adolescent growth peaks. Their cortical bone is thin and porous.

Climatic influences

Seasonal variations in growth

Guatamalan children grew most during the dry season, perhaps due to length of light.

Family size affects growth. Children from large families grow more slowly.

Smoking – reduces O2 to child, leading to low birthweight and other problems.

Alcohol – introduced toxin reduces O2 levels. Fetal alcohol syndrome – drinking in early pregnancy leads to smal body, head, facial deformities, organ problems and lower intelligence.

Psychological Stress leads to hormonally induced interference with androgens.

Lower Socioeconomic Status – cycle of poor nutrition, high stress and disease.

Weiner – English

Adaptive physiology – heat stress, metabolic “work” O2 consumption

We compare populations and study variation within populations by using histograms to compare means, ranges, and modes.

Pygmies

Eskimo Dinka

Why do people vary in terms of height, weight and fat distribution?

Figure 5.14 Bergmann’s RuleOur Origins, 2th Edition

Copyright © 2011 W.W. Norton & Company

Epidemiological Transition – Omran 1971:shift from infectious to non-infectious disease worldwide, whereby pandemics of infection are gradually displaced by degenerative and man-made diseases as the chief cause of death.

This change in disease pattern is closely associated with the demographic transition.

There are three phases of epidemiological transition during which heart disease, stroke and cancer replace infection as primary reasons for death.

In the Western world two-thirds of all deaths are attributed to these diseases.

As a culture’s sanitation, public health, and medicine improves epidemics become less intense and less frequent. The primary cause of death shifts from infectious degenerative diseases.

The shift is accompanied by increased life expectancy.

e) cholera killed most people in the US before the 1860s,but better sanitation in New York City led to TB, flu and Pneumonia replacing cholera as the main cause of death.

Epidemics – new diseases spread rapidly

Pandemic – epidemic on large geographic scale e) 1918 influenza.

Hunter-Gatherers –infectious diseases – parasites and zoonoses (lice, worms, sleeping sickness, tetnus, bilharzia are main causes of death, but there are few epidemics. Nutritional dieases are rampant.

Agricultural societies – more short lived microorganisms, increased populations size.

Epidemics such as small pox, measles, mumps, are rampant. Garbage, poor sanitation all increase the risk of epidemics. Fertilizer, feces, microorganisms are high.

Preindustrial cities – have rats and fleas, leading to epidemics like the black death.

Industrial societies – have good sanitation and have greater life span. Koru, Jewish tapeworm, and New World syndrome.

Demographic Transition – as a population becomes developed there are 1) reduction in death rate and 2) reduction in fertility rates.

3 stages of population demographics:

1) high mortality and high fertility (pyramid)

2) high fertility and low mortality (a transitional stages with more births than deaths, and the pyramid widening at the top).

3) low fertility and mortality rates (rectangular shaped population curves).

ex) before 1700 Irish people married late, after groom had inherited land from her father and a female a dowry. Only one son inherited land because agricultural output was low. Few men and women married.

Potato was introduced and did well, land was divided among several sons and passed on earlier. Populations grew.

Then a potato blight hit 5 years straight 1846-1851, 1.5 million died.

One million people emigrated. Irish returned to delayed marriages.

Migration prevented population growth.

In USA – few births in 1920s-1930s, few in depression of 1930s. Men returning from war had good jobs. Earlier marriages and shorter spacing between births.In 1958 fertility began to decrease. In 1986 1.8 children born per couple.

Linear Enamel Hypoplasias (LEH) – reflect nutritional stress.

Zhou and Corruccini - used hypoplasias to document historical famine in China 1959-1961. They found that rural subjects had greater incidence indicating their poorer nutritional stress. They also found a slightly higher incidence of LEH in females, indicating possible daughter neglect.