Genetics and Environment: a Debate on Human Growth and Maturation - Essay Example

Running Head: Biological Anthropology Genetics and Environment: A Debate on Human Growth and Maturation A Discussion Paper of Professor Date of Submission Essay Topic The current diversity of human beings is in part but not completely due to the ongoing evolution which has resulted in fluctuating gene frequencies in various breeding populations. However, the environment where in any human being grows up and matures is programmed to influence numerous of his/her phenotypic features. Genic activities, as argued in biological anthropology, will bring about different outcomes under different conditions. Most voluntarily observable characteristics are influenced to a lesser or greater extent (Merrell & Ingersoll, 1962). For instance, if we eat too much, we are reasonably likely to gain weight and no one can avoid observing this. A more thorough examination could show that a propensity towards obesity is determined by genes, but genes alone cannot bring about the entire change. Moreover, the environment where in we subsist has been greatly transformed by culture (Hanson, 1981). How much we eat and even what we eat depends quite insignificantly upon the naturally arising food sources in the locality. Most people depend upon the availability of food at the grocery store, their food preferences, and their available money to buy food. These are cultural forces. The argument of this essay is that biological anthropologists has constantly studied comprehensively and rigorously traits that are readily observable, in this case body proportions, with the intention of proving that the environment influenced them less or possibly not at all. It has been quite simple to remove environmental factors in studying bodily proportions, but not at all simple to identify their form of inheritance in a majority of cases. Understanding the genotype from a relatively forced phenotype is more complicated when biological anthropologists take into account other features of bodily and facial appearance wherein the current diversity of human beings is evident. The capacity of the environment to modify the activities of those genes which set up the possibilities for human growth and maturation is well-documented. But the way in which they do so and level of environmental alteration are not practically quite well-known or understood hence it is important for academics to study this area of human evolution thru the lens of biological anthropology. This study will attempt to verify the argument put forth by initially discussing the theoretical perspective underlying it, which is the Hardy-Weinberg Equilibrium Model, and then analytical approaches and evidence on the subject matter will be identified and analysed. Theoretical Perspective At present biological sciences commonly describe evolution as being the “sum total of the genetically inherited changes in the individuals who are the members of a population’s gene pool” (Swartz & Jordan, 1976, 161). It is apparent that the consequences of evolution are experienced by individuals, but it is the entire population that essentially evolves (ibid). For example, let us imagine that there is a characteristic that is established by the inheritance of a two-allele genes—A and a. If the original generation has 90% A and 10% a and their progeny communally have 92% A and 8% a, evolution has took place between the generations. The gene pool of the whole population has evolved in the path of a greater frequency of the A allele, it was not only those people who inherited the A allele who developed. This description of evolution was formulated primarily as an outcome of independent attempt in the first half of the 20th century by an English mathematician, Godfrey Hardy, and a German physician, Wilhelm Weinberg. Via mathematical inference grounded on probability, they assumed that gene pool frequencies are intrinsically constant but that evolution transpires in all populations practically consistently. They reconciled this evident inconsistency by studying the net impacts of possible evolutionary processes (Merrell & Ingersoll, 1962). Hardy, Weinberg and the subsequent generation of population geneticists come to a conclusion that evolution will not take place in a population if seven states are satisfied: (1) mutation is not taking place; (2) natural selection is not taking place; (3) the population is remarkably huge; (4) members of the population procreate; (5) all reproductive efforts are absolutely random; (6) everybody reproduces the same number of children; and (7) there is no movement in or out of the population (Merrell & Ingersoll, 1962). These circumstances are the absence of the forces that can bring about evolution. To put it a nutshell, if no processes of evolution are impinging upon on a population, evolution will cease to take place, hence the gene pool frequencies will be unaltered. Nevertheless, because it highly probable that any of these seven states, otherwise all of them, will take place in the actual world, evolution is the unavoidable outcome. This particular theory will be used in the analysis of the effect of environmental factors on bodily proportions. The theory’s premise on evolution will be employed to assess the extent of environment’s influence on the growth and maturation of human bodily proportions. Methods and Evidence Stature is one of the traits in which individuals diverge most evidently from one another and it is considered one of the aspects clearly influenced by conditions outside the individual genetic make-up. Better nutrition and health conditions throughout childhood definitely make individuals grow taller (Coon, Garn & Birdsell, 1950). But the discovery that monozygotic twins are almost identical in stature compared to dizygotic twins exhibits the power of its hereditary element (Osborne & De George, 1959). Biological anthropologists thus far are clueless about the genes that determine stature. It is a resulting trait, almost certainly influenced by sex hormones. The array of stature in the two sexes is quite remarkable, though, that a lot of women are taller than various men. In every population the average stature of a female is less than the average stature of a male, but the discrepancy is less defined among shorter individuals than among taller peoples. From birth to maturity, the overall body length normally rises about ‘three and one half times’ (Newman, 1962, 241). As people’s body mature, it turns out to be more difficult to stand up and the flexible discs between the vertebrae turn out to be less elastic. The elderly are not relatively tall compared to that when they were younger (ibid). Hardly any adult individuals are ‘less than four or more than seven feet tall’ (Coon et al., 1950, 44). No procreating populations have standard stature within ‘eight inches of these figures’ (ibid, 44). It is fascinating that the remarkably tall Watutsi, who make up the ruling class, instead of the population at large, subsist in direct proximity to the group of Pygmies whose average stature is ‘more than a foot shorter’ (Coon et al., 1950, 45). It is more common for neighbouring populations to be identical in stature, but the universal circulation of tall, medium and short individuals is quite uneven. As a common rule, populations living in temperate, damp climates and those subsisting in extremely cold ones are prone to be short, yet there are several exceptions. Various desert inhabitants and various groups home-grown to humid localities, particularly grasslands, are prone to be higher than the average stature. Throughout the earlier century and a half standard stature has risen in all countries where public health services and nutrition have improved. This boost in stature has totalled to six inches in some regions (Roberts, 1953). In examining the bare bones of olden Greeks, Angel (1946) discovered discrepancies from one century to another which may be linked to fluctuating economic situations. Stature is a dimensional feature, that is, it can be determined in centimetres or inches. Thus biological anthropologists have normally documented inter-population variations in terms of standards instead in terms of frequencies. In effect for several decades, a great deal of the work of biological anthropologists involved determining measurements of different parts of the body and afterwards computing that symbol of the average which is referred to as ‘mean’, (Washburn, 1953) along with some statistical constants. They discovered in the past that in any cohesive group such as procreating population, a vast many people have measurements which rest close to the mean, whereas merely a few have measurements which diverge to a significant extent. In some instances the concentration of big figures of individual dimensions is higher than in others (ibid). The degree to which a population is inconsistent is shown by the standard deviation. Roughly two-thirds of the members in a population will have measurements for any quantifiable characteristic within one standard deviation of the mean. Steps for computing the standard deviation, and the mean and for contrasting any two groups so as to determine how plausible it is that they actually vary from each other are discussed in several books and journal articles in biological anthropology (Washburn, 1953). For the purposes of this discussion it is only important to mention that in the proportions and dimensions of the body and of different body parts, various populations are as diverse as they are in traits for which specialists can compute allele frequencies. Due to the fact that the body’s dimensional attributes rely upon growth, as for instance blood types do not, environmental impacts have all the opportunities to influence the phenotype which is measured. Determining the phenotype from the genotype has been implausible under these conditions. For example, individuals could be short in stature due to poor nutrition or poor health throughout childhood, while they could be short due to genetic functioning (Merrell & Ingersoll, 1962). In a number of instances we are sufficiently knowledgeable about a specific population to generate a forceful or rational assumption; in others we can generate a knowledgeable deduction, but in most instances we plainly do not know. There is insignificant uncertainty that the different Pygmy inhabitants in the tropical areas of ancient Europe are short due to genetic functioning. The Scotch Highlanders, the Watutsi, and the Sioux Indians are tall as they have inherited the basic alleles. By itself, stature is in all probability not an adaptive feature, but there is sound basis to assume that it is a required manifestation of specific features of body physique which have been flexible (Newman, 1962). Weight, which is more reactive to one’s immediate environment compared to stature, is another manifestation. Roberts (1953) has shown a definite correlation between existing climate and average weight. Populations in which the average or typical weight of a fully developed male is more than 130 pounds are discovered nearly almost totally in warm and cold localities. Such areas are located in mountainous regions within the tropical region, obviously, just as temperate localities are at times located outside it. Tall persons could be thin and underweight. Such a body physique is normally located among dark-skinned populations of high stature in tropical regions. Short individuals could be small or stout. Much more frequently than not, short inhabitants adapted to cold areas are chunky in physique, while short people local to temperate regions are small (Roberts, 1953). The rules of Bergman and Allen have relevance to Homo sapiens. Humanity’s cultural accomplishments have allowed or even promoted a particular extent of avoidance of these rules. Most people love to eat, and this predilection can increase their weight, even if they inhabit a tropical region. In several societies, status builds up to those who show their affluence by eating too much or becoming fat, or by nourishing their mates for them to get fat. Wealthy individuals can do this. Impoverished individuals, who should undertake manual or physical labour, cannot. Groups of people living at an extremely deprived subsistence level are populations most prone to conform to the rule that, in order to move and function most capably in tropical regions, one must be of light physique and not gain substantial weight. Technologies has also enabled quite far-reaching movement of people, and at present anthropologists discovered several groups of people which have not yet adjusted physically, genetically or phenotypically to their existing environment (Hanson, 1981). Roberts (1953) discovered that Mongoloids, whose predecessors perhaps lived almost permanently in a cold terrain, are less inconsistent in weight in reaction to climate than are Africans or Europeans. Mongoloids have a tendency to be fairly sturdy in physique, regardless of their place of residence. Those who live in tropical areas are normally short but not actually stocky. Africans, excluding the Pygmies, have a tendency to be tall for inhabitants in the tropics. Those who inhabit dry regions are normally quite lean (Roberts, 1953). Limb proportions and weight and stature are features of body physique which have perhaps had adaptive importance when technology was insufficient. A number of desert inhabiting natives, such as the Papago of Arizona, have large torsos but rather skinny limbs. Because there is an accumulation of sweat glands from the elbow to the wrist, long limbs could allow adequate loss to allow survival throughout the warm daytime hours when manual labour should be carried out, while the torso is large enough to preserve heat throughout night-time (Swatz & Jordan, 1976). Eskimos are much more prone to have squat limbs than they are to have thickset body builds. Their bodies, when hunting, are clothed in very thick furs but their extremities, such as their hands, may have to be taken out from the fur from time to time (Hanson, 1981). Generally, the indigenous peoples of tropical Melanesia and Africa have fairly long extremities, while those native people of eastern Asia and the neighbouring land mass are short. The lower legs and forearms are particularly extended among Africans. In most cases, taller people have extended limbs in proportion to the size of the body. But these are probabilities, not inflexible rules. The boost in stature throughout the past generations is not attended by any modification in relative length of the limbs in the populations studied (Coon et al., 1950). This suggests that the body proportions are less flexible than its original size, which is evidently prone to significant environmental modification. Size measurements, such as those of the hips, chest and shoulders manifest the effects of sex and age and lineage. It is recognised that for useful reasons related with childbirth, females as a rule have wider hips than males in proportion to their shoulder width and stature. In spite of this fact, there is a significant convergence in relative hip size between females and males. Not every male has favourable masculine builds nor do every female has favourable feminine physiques. The hips have a tendency to enlarge during maturity but the shoulder width stays more roughly unchanged, even though the elderly may not be able to sustain their maximum breadth (Osborn & De George, 1959). Among African Negroes ‘sexual dimorphism in the shoulder-hip index’ (Hanson, 1981, 97) is less defined than among majority of other populations. This could be related to the length of build which is normally seen in Africa. The size and depth of the chest are normally, but never consistently, greater among those living in the mountains than among those in lowland areas. It would appear logical to assume that larger lung capacity would have contributed to the survival capacity of those who inhabit the highlands and those who spend a substantial amount of time climbing (Hanson, 1981). Simultaneously, chest measurements could be enlarged by exercise, in order that we cannot be certain that natural selection has been necessary. The depth of the chest enlarges during maturity, though as in the condition of widening hips, this is an indication of aging instead of enhanced function (Merrell & Ingersoll, 1962). The proportions and sizes of the head and face have been documented for groups of people in most countries around the world. Anthropologists have discovered some important and several small geographical variations. Because skulls have better enduring features than majority of other bones, sufficient of them from primitive periods are accessible to allow us to compare ancient and recent forms of human beings, as well (Swatz & Jordan, 1976). Evolutionary anthropology illustrated ways in which the attributes of the skull, and accordingly of the head and face, have evolved throughout the evolution of humans. The extent to which living individuals vary from one another in the standard dimension and form of the head and its different parts is significant, and predominantly, mysterious; quite few traits have a relatively evident adaptive importance. Reasonable inferences have been made to explain for a number of factors of differences, but we stay quite uninformed of the explanations for the higher number of variations (Swatz & Jordan, 1976). The measurement of the brain as shown by the cranial capacity has evident practical importance. Brains below a particular bare minimum dimension are insufficient to control a human body efficiently, but in no populace does the average cranial capacity approach close to such a low dimension. The size of the brain is linked to the size of the body. As a result males have on average bigger brains than females and populations in which the standard size of the body is big are prone to have big brains as well. Furthermore, an orb is the most efficient shape of container. A broad or high vaulted skull could be short and still give adequate cranial capacity. Several of the large, heavily built, brachycephalic inhabitants of Polynesia, North America and Siberia have the biggest standard cranial capacities of any existing human beings: ‘1,500 cubic centimetres or more for adult males’ (Hulse, 1963, 333). Central and northern Europeans, northern Chinese and Japanese have cranial capacities which ‘average well over 1,400 cubic centimetres’ (ibid, 333). The smaller inhabitants of temperate regions of Africa, America, Asia and Europe as a general rule, have cranial capacities which ‘average between ‘1,300 and 1,400 cubic centimetres’ (Hulse, 1963, 333). A number of Pygmy inhabitants and the indigenous peoples of Australia have ‘average cranial capacities of less than 1,300 cubic centimetres’ (ibid, 334). The variety in brain size in each of these populations is at least as large as the variety in body size. A number of Siberians have smaller brain sizes compared to a number of Australians, and numerous Africans have much larger ones than numerous Europeans. Brachycephaly implies broad-headedness, and an individual is identified as brachycephalic if his/her head is ’82 percent as wide as it is long’ (Coon et al., 1950, 63) s/he is identified as dolichocephalic, which means long headed, if the percentage is ’77 percent or less’ (ibid, 63). The proportion between the breadth and length of the head is referred to as the ‘cephalic index’ (Coon et al., 1950, 63). Majority of Paleolithic populations were dolichocephalic, but a remarkable majority of existing populations are not (ibid). Osbome’s and De George’s (1959) twin studies showed a high level of heritability in cephalic index and head size, and there is to a certain extent questionable substantiation that these characteristics are because of dominant alleles. Yet environmental alteration of cephalic index, initially shown by Boas (1911) has been demonstrated in several later studies. The head length is directly correlated to stature, but its size is not. A boost in stature, in European population, is normally escorted by a reduction in cephalic index, due to the fact that the head lengthens without broadening. This does not seem to be case in relation to the groups of people of eastern Asia, though. Females normally have somewhat higher cephalic indices compared to males of the same populace. It has been acceptable among a number of native peoples to shape the heads of their infants while the sutures remain wide open, changing the form in one way or another (Boas, 1911). This practice has greatly irritated biological anthropologists, because the consequence is enduring. The proportional frequency of brachycephaly is low throughout a great part of Melanesia, Australia and Africa. Populations subsisting in such far-flung regions as Tierra del Fuego, Lower California and Greenland are predisposed to be even more dolichocephalic. In populations living in Europe, the standard is lower in southern Italy, the Iberian Peninsula, Scandinavia and the British Isles than anywhere else. The greatest averages are located in a belt of land ranging from Siberia through central Asia into central Europe and the Near East. But the higher number of indigenous groups of America, the Pacific islands, or Southeast Asia is also brachycephalic. The differences within each population is higher than the variation between the standards of any two identified populations, hence there is much overlapping (Hulse, 1963). The total size and shape of the face, as demonstrated by different indices, is as inconsistent as the size and shape of the skull. Men usually have larger faces than women just as they have larger brains. This is basically a characteristic of their larger size in most cases. Faces which are somewhat narrow and long are more widespread in the mountainous region ranging from the Balkans through the Middle and Near East, and the length of Europe’s Atlantic coast than they are in other sections of the globe. Faces which are wider and smaller are relatively common of Australia and Africa, while egg-shaped faces are common in much of India and the Mediterranean basin. The standard size of the forehead is large in Europe, particularly in Western Europe, but the contrary is valid among the groups of people in the Pacific (Hulse, 1963). In his exploration of the Pitcairn and Norfolk Islanders, who are the crossbreed progeny of Polynesian and British forebears, Shapiro (1936) revealed evidence which indicates that constriction of the forehead is caused by a dominant allele. Large size of the jaw is most commonly discovered among Eskimos, and constriction among European Basques and South African Bushmen. Several traits which are readily discernable are not that easy to quantify: for instance, the shape of the ear, the presence and degree of creases of skin sagging over the eyelids, the height of the nasal bridge. In each of these traits and in other features as well, groups of people as well as individuals vary to an evident degree (Shapiro, 1936). We know thus far little or even nothing of the form of heredity or the adaptive essence, if any, of these features. Some eccentricity of one or another could illustrate a family ancestry, as is the case of one of the previous royal families of Europe, the Hapsburg, which had sagging lower lip; or a petite genetic segregation, such as the extremely prominent noses of people in the Moghegno village or of those in Pitcairn’s Islands; or an immense congeries of interrelated procreating populations, for instance, the epicanthic eyefold quite common among the populations of eastern Asia (Hulse, 1963). We can observe that these traits are present and they are at times functional as diagnostic standards, but clarifying them is a different issue. Even more challenging to manage from the perspective of biological anthropology are such theories as basal structure and metabolism. Both of these notions have a medical function for general practitioners, and there is a great deal of difference in each, among the frequencies or averages of individuals and populations. But each appears to be the ultimate outcome of a vast number of insufficiently described and interrelating causes (Hulse, 1963). Robert (1952) has demonstrated that basal metabolism is linked to race, to weight, to stature, and to climate. Constitutional form can be identified by observation, yet nobody has yet described any specific constitutional form just sufficient to make important relationships probable (Hanson, 1981). There is little uncertainty of the possible function of both notions, but thus far we cannot apply either in any categorisation of the racial diversities of man. Conclusion The evolution of the different forms of life, consisting of human life, has been absolutely reliant upon the responses between genetic functioning and the immediate environments of the groups of people concerned. Had either been diverse anyhow, the outcomes of their relationship would have been diverse as well. There is no divergence between genetics and environment: their combined response generates the traits of all living things. This is important to remember, for the reason that there have been quite numerous efforts to construct a dichotomy between them. In researches, we should keep one of the two forces unvarying if we are to determine an adjustment in the other. Racial diversity is present within the human species at present as it did in earlier periods. Certainly, it could look like that the degree of diversity has enlarged in the course of time. We are capable in unearthing numerous things from examining a living person which an investigation of the skeleton and bones alone could not enlighten us. The bones are just a component of the body, and mature bones are prone to be incomplete. On the contrary, the living body provides us knowledge about biological mechanisms as well as anatomical systems. The emergence of growing diversity within the species could be misleading, basically due to our ignorance about ancient populations. But the most well-known categorisations of races are founded upon the belief that evolution has resulted in increased human diversity. Bibliography Primary References Angel, J. (1946). Social Biology of Greek Culture Growth. American Anthropologist , 223-233. Baker, P. (1958). Racial Differences in Heat Tolerance. American Journal of Physical Anthropology , 287-306. Boas, F. (1911). Changes in Bodily Form of Descendants of Immigrants. Government Printing Office, Washington . Candela, P. (1942). The Introduction of Blood Group B into Europe. Human Biology , 413-443. Roberts, D. (1952). Basal Metabolism, Race and Climate. Journal of the Royal Anthropological Institute , 82, 169-183. Roberts, D. (1953). Body Weight, Race and Climate. American Journal of Physical Anthropology , 533-558. Newman, M. (1962). Evolutionary Changes in Body Size and Head Form in American Indians. American Anthropologist , 237-257. Washburn, S. (1953). The Strategy of Physical Anthropology. Anthropology Today . Weiner, J. (1954). Nose Shape and Climate. American Journal of Physical Anthropology , 1-4. Review Article Kuzawa, C.W. & Quinn, E.A. (2009). Developmental Origins of Adult Function and Health: Evolutionary Hypotheses. Annual Review of Anthropology. Secondary References Coon, C., Garn, S.M. & Birdsell, J.B. (1950). Races. Springfield: Thomas. Hanson, E. D. (1981). Understanding Evolution. New York: Oxford University Press. Hulse, F.S. (1963). The Human Species: An Introduction to Physical Anthropology. New York: Random House. Merrell, D. J. & Ingersoll, O.J. (1962). Evolution and Genetics: The Modern Theory of Evolution. New York: Holt, Rinehart and Winston. Osborne, R. & De George, F.V. (1959). Genetic Bias of Morphological Variation. Cambridge: Harvard University Press. Shapiro, H. (1936). Heritage of the Bounty. New York: Simon and Schuster. Swatz, M. J. & Jordan, D.K. (1976). Anthropology: Perspective on Humanity. New York: John Wiley & Sons. Read More