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Read this essay to learn about the heredity.
Essay on Heredity # Meaning:
Sandiford defines heredity as “the sum total of the potentialities possessed by an organism in the zygote stage of its existence”. A zygote is the first beginning of life in the mother’s womb. It is a single cell, a fertilised ovum, the egg-cell in the mother successfully fertilised by the spermatozoon from the father.
The zygote contains the complete potentiality of the future individual. “Heredity is a constant factor, established at the time of conception.” It is something innate, the very nature of the organism. Environment, on the other hand, consists of all the changing influences which impinge on the hereditary factor and brings out the potentialities inherent in the zygote. “The environment is that which surrounds the individual and makes actual what was only potential. The environment consists of all conditions and factors which affect an organism from without.”
An individual is what he is, due to his heredity and environment. There is a constant interplay between these two factors. It is impossible to ignore any of them. Two identical twins look very much alike and behave also very much alike because their heredity is very nearly identical. But soon differences in aptitudes, testes and temperaments begin to appear and we say that these differences are due to different environmental factors.
For the same reason, siblings show marked similarity, not only in physical traits but also in personality characteristics. But it would be wrong to suppose that heredity is responsible for all similarities, and that environment is responsible for all differences.
At the zygotic state all human organisms look very much similar, and even if the environment is similar, each zygote would grow up into a different individual. The differences in the heredity will show up. The children of Bengali parent’s will grow up different from the children of Australian aborigines. Even two siblings (brother, sister from the same parents) do not possess the same hereditary factors and this is one of the reasons why in spite of a large number of striking similarities, they would be different in certain respects. So it is wrong to suppose that heredity is the antithesis of variation. “Heredity includes all traits both like and unlike.”
It is true that the zygote formed of dogs will develop into a pup and not a lion cub, or a human infant. In spite of adverse circumstances heredity shows itself. “Race remains remarkably constant from generation to generation, despite marked changes in the environment.” But it would be wrong to conclude that heredity is a mysterious force which is inevitable like fate.
When we understand the physical basis of heredity, we find that it is neither a force, nor is it entirely mysterious. Moreover, we shall see that though the environment influences heredity, it cannot change heredity in its essentials.
Essay on Heredity # Features:
Heredity May be the Cause of Difference:
“Paradoxical as it may seem, heredity may sometimes make a child unlike his parents.” Sometimes we find a child with light skin born of parents with rather dark skin. Or, we find a child markedly superior to his parents in intelligence. Here the explanation of the phenomena is not to be sought in environment, but rather in heredity itself.
We should remember that “the child’s heredity is derived not from its parents alone, but from the entire stock to which it and its parents belong”…”a child’s brightness is not just an average of the brightness of the two parents; it is a composite in which all the traits of the stock may be shuffled and reshuffled. Heredity is an impersonal sort of thing, necessitating the study of the whole family, stock and race.”
Environment May be the Cause of Similarity:
Again, the environment may be the cause of uniformity, rather than of difference. That all Bengali children speak the same language, that all English children have similar food habits, that all pupils of the same Public School have a similar handwriting, are all due to the uniformity imposed upon by the environment.
Internal and External Environment:
Heredity and environment are two distinct factors but they are interdependent. We said that, relatively speaking, heredity is a constant factor established at the time of conception. The individual’s environment, on the other hand, is continually expanding.
“The most obvious environmental influences are those which act upon the organism from without, and especially those which operate after birth has occurred. There exists, however, an internal environment, which, at the earlier stages of development, is more influential than the external environment. It has been found that the hereditary dispositions can do this work only by guiding the course of development along one rather than another line, while the environment of the mother’s body maintains specific chemical conditions, supplying food and the other ways shaping the individual’s growth___ After the time of birth it is the outer environment that guides, releases, and gives expression to hereditary potentialities.”
The reference here is to the blood, lymph, and the other physical and chemical elements in the mother’s womb where the embryo grows. “From the relatively simple chemical environment of the newly conceived organism we get, eventually, the highly complicated social environment of people, books, schools and so forth.”
Heredity and Environment are Correlative:
If we are to understand the complete nature of an organism, it will not do to trace the hereditary factor alone, or the environmental factor alone. A rectangle is the product of its length and breadth. Both have to be taken into consideration, if we want to determine the area of the rectangle. Similarly, a child is a unique specimen of personality which is the product of his heredity and his environment.
“Environment is simply the correlative of heredity; it merely determines which, and to what extent, hereditary trails shall be developed. It is a false belief that a change in environment will lead to a change in heredity, and that these changes are transmissible to off-springs. After thirty years of experimentation upon plants, animals and human beings, science can say with a great deal of assurance that there is no ground for this popular belief.”
As Davenport says, “Environment affords the stimulus, heredity determines largely the nature of the reacting substance; the reaction or behaviour is the resultant or product of the two.” An individual comes to the world with his hereditary capital gathered not only from his parents but from all his forefathers. But that is only half the story. The capital has to be invested in the market, we call the society. The education that he receives in the home, from his neighbors, from his teachers and fellow-students, from books, through social intercourse, the thousand influences that impinge on him, either bring out what is inherent in him or thwart and frustrate his inner potentialities. What he actually becomes, is the result of his heredity as crossed by his environment.
“Heredity or nature provides whatever potentialities we possess; environment or nature determines whether or not they shall be realized in actuality. A Beethoven born in the depths of an African forest or in the wilds of Patagonia would never compose beautiful sonatas and symphonies, although he might, and probably would, become the best tom-tom beater of his tribe.”
A tone-deaf person, on the other hand, though taught by the best teachers of music, would never become a musician. But it is also true that an average intelligent child, when properly trained, will do much better than a naturally bright child, who has been neglected. The improvement brought about in a particular child, however, cannot be transmitted to a later generation.
But “although parents cannot pass on their knowledge and learning, yet in a very real way the knowledge, laws, customs and traditions of mankind descend from generation to generation. Mankind through countless generations has stored his acquisitions of knowledge in books, pictures, works of art and utility, laws and traditions”.
These we call the social heritage of the individual. “These become environment stimuli of powerful potency to succeeding generations, providing, of course, that they have the natural intelligence to profit from them.” It is this double truth that Sandi-ford stresses when he says, “children are born with a biological heritage; they are born into a social heritage.”
Essay on Heredity # Effective Environment:
It is now established beyond doubt that environment affects heredity. But the apparently same environment does not affect even similar individuals, in exactly the same way. There is something unique in each individual and this is what determines his particular reaction to a particular situation. What acts as an ‘environment’ in one individual does not serve as an environment in the case of another individual.
So, sometimes the term ‘effective environment’ is employed. When out of the innumerable surrounding factors, an individual takes note of certain stimuli, to the exclusion of others which are equally plausible, we call it ‘the effective environment’. Thus, all students in the same class, so long as they are participating in the class work are being subjected to the same environmental factors. But each student responds only to a particular cross-section of the total environment. This becomes all the more striking, when we consider siblings in the same family, or even more particularly, identical twins reared up together.
Here we find that in spite of the apparent uniformity of the environment, to each individual the ‘effective environment’ is different. “What shall be ‘effective’ depends on the particular individual, on his heredity, his previous experience, his chronological age and his mental equipment. Two children in the same home do not necessarily have the same effective environment, and the more children differ from each other, the greater difference there is in their effective environments. And it has to be remembered, though the heredity is apparently the same, “what is ‘inherited’ in one environment makes a difference in the appearance of the hereditary disposition.”
What is More Important?
Heredity is fixed, and the environment is flexible. But they are correlative factors. The question has been agitating biologists, educationists, social workers, and psychologists, that is, all- people who are interested in human development, as to which of these two correlative factors is the more important.
“No wonder they become excited, for in this bald form the question is unanswerable, and really absurd. It is like asking whether it is more important for a motor car to have an engine or some petrol. If you want to raise cabbages, which is more important—to have some cabbage seed or to have a place to plant them? Without a proper environment the seed would not germinate and develop, and without seed, there would be nothing to develop. If you are thinking of a single individual, it makes no sense to ask whether heredity or environment is more important, in his development and behaviour. Each of them is absolutely essential.”
Essay on Heredity # The Physical Basis:
Heredity is a complex mechanism and we do not yet know the complete answer to all its secrets. Yet the beginning of life is deceptively simple. An ovum in the female body is fertilized by a spermatozoon from the male and life begins as a single fertilized cell in the mother’s womb. The fertilized cell or zygote is smaller in size than the head of a pin. The single cell body begins to break up into many and gradually takes shape as the foetus in die mother’s womb.
Each cell has a nucleus surrounded by cytoplasm which protects and nourishes it. “The determiners of heredity are complex organizations of chemical materials within the nucleus. More specifically, they are contained in nuclear structures, which because they show up when stained are known as chromosomes.”
The nucleus contains little rod-like bodies called chromosomes, some of them longer and some shorter, some straight and some curved, but always the same number of them in all the cells of the same individual and in all individuals of the same species. Every human cell contains 48 chromosomes; in some animals and plants, the number is much smaller or even much larger than this. Instead of speaking of 48 human chromosomes, it is better to speak of 24 pairs; the fact that they come in pairs is very important.
The nucleus of the fertilized ovum, then, contains 24 pairs of chromosomes. One chromosome of each pair came from the spermatozoon, while the other was present in the ovum before fertilization. The child gets one chromosome of each pair from his father and the other from his mother. Females have twenty-four pairs. Males have twenty-three pairs, plus two singles. One of them, the Y chromosome is found only in the male. Females have a pair of X chromosomes, while males have X and Y. The X and Y are called sex-chromosomes, because our sex depends upon whether we get the XX or the XY combination.
Three important points on heredity should be clearly remembered:
(1) The child’s heredity is derived from both his parents;
(2) It is fixed and determined at the moment of fertilization or conception—no additional heredity can get into him later, even from the mother who carries him and provides his nourishment for the next nine months;
(3) His heredity pervades his entire organism, being present in every one of his cells.
Essay on Heredity # Laws:
Gregor Mendel (1822-1884) was one of the first to make a detailed study of the mechanism of heredity. Though a priest, he was a person with a keen scientific mind. He made experiments on garden peas and tried to determine the precise results of hybridization (1866). He observed the results of mixing round and wrinkled peas. He noted that peas had only seven stable definite characteristics, which were transmitted without change to later generations. These he called the ‘unit characters’.
Thus, for peas, roundness and wrinkledness are ‘unit characters’. For men, blue eyes and black eyes are unit characters. Mendel’s experiments, which were first published in the Proceedings of the Natural History Society of Brunn, attracted little attention at the time. But in 1900, De Vries, Correns and Tschermak each independently rediscovered the law established by Mendel. Since that time, Mendelism has dominated biology. Mendel’s ‘unit characters’ were renamed ‘chromosomes’. Experiments were extended to quick-breeding animals like mice, rabbits, guineapigs, etc.
Since 1910, experiments on the quick-breeding fruit-fly (Drosophila Melangoster), a species which exhibits a large variety of new modifications and is easy to breed in the laboratory, has yielded many clues to the understanding of the mechanism of heredity and confirmed the general conclusion arrived at by Mendel.
Mendel observed that if a pea which has a wrinkled skin (WW) when dried, is sown and crossed with a pea which remains round when dried (RR), the resultant peas of the first filial generation (F1), are all found to be round (RW). Not a single wrinkled pea appears. If now these round peas are sown and crossed indiscriminately among themselves, the crop of the second generation of peas (F2), is found to contain 3 round peas to 1 wrinkled pea.
The wrinkled peas of this generation are ‘pure’, which means that if they are sown and self-fertilised (i.e., crossed indiscriminately among themselves) they produce only wrinkled peas. But the round peas are of two kinds. One- third of them, or 25% of the (F2) crop breed pure round peas; the other two- thirds or 50% of the (F2) crop behave in the same way as the (F1) crop did. They produce round and wrinkled peas in the proportion of 3 to 1. All later generations follow this same pattern.
Mendel noted that when the possibility of two opposite characters (e.g., roundness and wrinkledness) are implicit in an ‘impure’ pea, only one character comes out, when sown (in the case of peas it is roundness). This he called ‘dominant’. And the character which, though implicit, fails to show up, he calls ‘recessive’. In the case of peas, the dominant character is roundness. Wrinkledness is a ‘recessive’ character. Mendel was not only a careful experimenter, but he had also the genius to interpret his results correctly.
Mendel’s explanation contains three fundamental elements:
(1) “Independent unit characters. Any organism, although physiologically a unit, from the standpoint of heredity, is a complex of a large number of heritable units. Roundness or wrinkledness, for example, is independent of the nature of the plant as a whole. Each is an independent unit. The plant may be tall or short, but the roundness or wrinkledness of the ripe peas is unaffected by the size of the plant.
(2) Dominance. Certain characters, like roundness or tallness dominate and become visible when present, even though wrinkledness or dwarf-ness is present also. The opposing character which recedes, as it were, in the presence of the dominant one, is called the ‘recessive’; if however, the dominant is not present, the recessive character shows.
(3) Purity of the Gametes (reproductive cells). A better name for it is segregation. The reproductive cell can only contain one of the two alternative characters. It can, for example, contain the character for roundness or wrinkledness but not both. If two germ-cells, each containing the factor for wrinkledness, unite to form a zygote (fertilized egg), the resultant pea will be wrinkled; if each contains the factor for roundness, the pea will be round.
If one contains the factor for roundness and the other the factor for wrinkledness, the pea will be round, owing to the dominance of roundness. Alternative characters are segregated in the formation of the germ-cell, and so no germ-cell can contain both.”
Essay on Heredity # The Gene or Factorical Hypothesis:
How do such a small number of chromosomes account for the innumerable traits of the individual organism? The answer was also discovered by the researches of later biologists, particularly of Morgan, who found that the sex-chromosomes (XY in the male and XX in the female) differ in some very important respects, from the other chromosomes in the cells of the body.
Modem biologists beginning with the findings of Mendel have concluded that chromosomes are the bearers of heredity. But these are not the ultimate units of heredity. Morgan and his co-workers have shown that different sections of the chromosomes behave quite differently so far as inheritance is concerned. In heredity, these parts behave as units. Morgan calls these hereditary elements ‘genes’ or ‘factors’.
“The elementary genetic factors or genes were first discovered by comparison of parents and children when the parents were different in certain respect? Later, it was found possible to localize certain genes in certain chromosomes, and even in certain parts of a chromosome. Examined under the high powers of the modern electronic microscope, a chromosome is seen as somewhat like a string of beads, and essentially it is a string of genes, arranged in a definite order.
“The human genes probably number a thousand or more, distributed unequally among the 48 chromosomes. The genes—like chromosomes—come in pairs, one gene of each pair from the father, and the other from the mother. For the most part, the genes of a given pair are alike and give rise to resemblances rather than the difference between parents and the child; the resemblances greatly outnumber the differences. But in certain pairs the genes may differ, one tending to produce brown eyes, for example, while the other tends to produce blue eyes. If a child has a pair of brown eye genes, one from each parent, he will have brown eyes; if each parent has given him a blue-eye gene, he will have blue eyes; but if he got a brown-eye gene from one parent and a blue-eye gene from the other, his eyes will be more or less brown, for the brown-eye gene is dominant over the blue-eye gene”.
Even the most powerful microscope has been unable to identify the gene. “They are assumed to be packets of chemicals. Then geneticists discovered that the salivary gland of the fruit-fly contains exceptionally large chromosomes which when viewed microscopically, have dark and light bands throughout their length. The genes were thought to be in these bands”.
Essay on Heredity # The Discovery of DNA:
A very important breakthrough in biology has been effected by the recent discovery of the “hereditary chemical” in the shape of the deoxyribonucleic acid (DNA) molecules. Dr.James Dewey Watson (Harvard University) and Dr.H. C. Crick (Cavendish Laboratories of Cambridge University) won the Nobel Prize in 1962 for their “contribution to the understanding of the basic life-process through the discovery of the molecular structure of the DNA, the substance of heredity”.
Even as early as 1871, a young Swiss biochemist Meischer “had isolated nucleic acid from the sperm of the salmon. He believed that this nuclear substance must play an important role in cellular activity”. “But the findings of Mendel and Meischer were ignored by an unprepared scientific world and buried in learned libraries for many years. In the interim period between the uncovering of Mendel’s and Meischer’s discoveries, the unit factors or genes were shown to be located within the chromosomes of all cell nuclei. Chromosomes were found to be composed of nucleic acids and proteins”.
“With interest centred on proteins, little attention was given to the nucleic acid till 1944. At this time, Avery, MacLeod and McCarty at Rockefeller Institute provided the first experimental evidence that de-oxy-ribonucleic acid (DNA) transmits genetic information. Their evidence seemed to point to the fact that the individual organism has its own specific type of DNA that carries genetic instructions. Experimental proof rapidly accumulated to confirm DNA as the component substance of genes”.
Thus DNA, like a master-blue-print, provides information for the synthesis of thousands of specific proteins within living cells. Calculations show that the DNA in the nucleus of each human cell contains some five billion base pairs divided among man’s forty-six chromosomes (barring the 2 sex chromosomes XX & XY). The DNA endowment conferred by parents on their progeny is stored within sex cells. A fertilised egg contains a microscopic amount of DNA from each parent that provides instructions for the kind of off-springs that will be formed. DNA has bridged the innumerable gaps between generations back to the beginning of life on earth.
Essay on Heredity # Why is Each Individual Different?
When two children with apparently identical heredity (e.g., identical twins) are brought up in strikingly different environment they grow up with important difference is understandably due to the difference in the environment. But if the complex mechanism of heredity is kept into view, it will be clearly realised that the environment alone does not explain all differences. The heredity also contains factors responsible for differences.
Siblings have similar chromosomes, but they are not identical. Even identical twins, though they are genetically identical, are perhaps different in the arrangement of the gene-factors and their DNA. Moreover, every individual responds selectively and differently to his environment, though apparently the environment (both external and internal) may appear to be the same. That is why, no two persons may be exactly alike. As every fingerprint is singularly unique, so every individual human being is unique and unrepeatable.
Two Extreme Views:
The question whether physiological differences, differences in intelligence, temperament, and personality are due mainly to heredity or environment continues to be a strongly debatable point. Two extreme views may be indicated.
(a) Galton, Karl Pearson, Estarbrook and many others stoutly hold the view that a man is what he is, because of his heredity. Heredity determines the differences between individuals and races. Environment is of secondary importance. The physiological make-up of an individual—the basic factors of personality are hereditary. Even such relatively unimportant details such as complexion, colour of the eyes, texture of the hair etc. are hereditary.
It is the genetic factors which are responsible for differences between species. Mental dispositions such as boldness or timidity, frankness or distrustfulness are found to run in families. Saints as well as criminals are born. Any influence that the environment exerts on personality-formation is only peripheral. Their conclusion is summed up in the statement – You cannot make a silk purse out of a sow’s ears”.
On the other hand, Helvetius, Rousseau, Robert Owen and almost all communist writers are firmly of the opinion that, it is the environment that moulds the individual. Through proper training, proper opportunities, favourable and enriched environment any individual may be moulded into a fine personality. No person is born a saint or a criminal.
Even intellectually retarded children show wonderful improvement if they are properly and intelligently handled. Watson boasted that, given suitable opportunity, teaching aids, proper environment, he could train up any child into a moderately successful doctor, engineer, advocate, poet, or trader; conversely, he could condition a child from the best family into a thief, robber, or beggar.
The mass of materials collected through scientific observation, statistical computations and to a limited extent by experiment is formidable. Both sides claim to depend on such scientific evidence. But personality is such a complex affair and the evidence tendered by both sides are so contradictory, that it is evident that the last word has not yet been said on this absorbingly interesting issues.
On a careful comparison of the evidence, it also becomes clear that heredity and environment are not contradictory concepts but complementary to each other. The problem is not heredity vs. environment, but heredity and environment and it is necessary to determine the amount of contribution of each factor.
Studies on environment and heredity may be grouped round the following topics:
(a) Family history and family resemblances.
(b) Life-history of famous (or infamous) men with special reference to their environment.
(c) Identical twins, fraternal twins and siblings—their comparison.
(d) Children (specially twins) reared apart from early childhood and comparison of their differences and their comparison with children of their foster homes.
(e) Children brought up from infancy or later, in orphanages and vagrant homes.
(f) Individuals brought up outside of human society, individuals belonging to a-social and anti-social groups.
(g) Relation between the economic and social status of the father and children, etc.
Essay on Heredity # Studies in Family History:
The studies have generally been conducted by psychologists believing in the efficacy of heredity. In 1826, Galton published his interesting book “Hereditary Genius”, embodying his laborious studies on the family history of Galton’s and Darwin’s. Karl Pearson, in later years, carried on the research of Galton by tracing back the geneology of the three famous families of England, viz. Wedgwood’s, Galton’s and Darwin’s a thousand years and published his studies under the title “The Life, Letters and Labours of Francis Galton, Vol. I. Pedigree plates”. Both these studies show that a long line of eminent scientists, ministers, church dignitaries, philosophers and literary men came from these three families related to one another by blood and by marriage.
The most remarkable record belongs to the family of the Darwin’s. In this family, five great scientists, who were elected fellows of the English Royal Society, came in a direct line. From these studies Galton and Pearson have sought to establish the conclusion firmly that genius is a matter of good heredity—that ‘blood tells’.
The evidence marshaled is undoubtedly impressive. It does prove that heredity is a very important factor. But the studies suffer from the defect of oversimplification. They have both failed to take note of the environmental factors altogether. The eminent men referred to in these studies also enjoyed the advantage of an enriched and favourable environment which certainly contributed to their eminence.
Two very interesting studies of materials of a quite different kind are provided by Dugdale’s —The Jukes (1877), and Goddard’s—The Kallikak’s family (1914). Both these fictitious names belong to American families who have to their discredit a long line of criminals and fallen women. Both Dugdale and Goddard seem to have confirmed Lombroso’s thesis that crime is hereditary—that “it runs in families.”
Dugdale was the Superintendent of the large New York prison. It struck him that many inmates of the prison bore the family title of Juke. Dugdale instituted a painstaking investigation of their family connections and history. The family was resident at the time of investigation in upper New York, but later scattered over fourteen States. The family history provides grim material. Dugdale studied 709 persons, 540 being of Juke blood and 169 of ‘X’ blood who had married into the Juke family.
Of the 709 persons he studied, 180 had either been in the poor house or received outdoor relief. There had been 140 criminals and offenders, 60 habitual thieves, 7 lives sacrificed by murder, 50 common prostitutes, 50 women venereally diseased, contaminating 440 persons and 30 prosecutions in bastardy. The total cost of the State of New York of this one group of mental and social degenerates was estimated, for a period of 75 years, beginning in 1800, at $ 1, 308, 00.
The family history of the Kallikaks compiled by Goddard is equally depressing. “The common ancestor in the Kallikak family was Martin Kallikak (name fictitious) a young soldier of the Revolutionary War. During the campaign Martin had a son by a nameless feeble-minded girl, from whom 480 individuals had descended in direct line.
This line has never been an asset to the world. On the contrary, 143 of these descendants are known to have been normal. The rest are unknown or doubtful. Thirty-six have been illegitimate, 33 sexually immoral, 24 confirmed alcoholics, 3 epileptics, 3 criminals, 8 keepers of houses of ill-fame, and 83 children so feeble that they died in infancy.
Now comes a turn for the better, in family history. “After the war, Martin married a Quakeress of good stock and from the union 496 descendants has been traced. All of these, except two, were of normal or supernormal mentality and morality holding positions as lawyers, doctors, teachers, traders, governors, professors and presidents of colleges and universities. This line of children apparently could not turn out badly in any environment”.
Goddard confidently draws this conclusion:
“The fact that the descendants of both the normal and the feeble-minded mothers have been studied and traced in every conceivable environment, and that the respective strains have been true to type, tends to confirm the belief that heredity has been the determining factor in the formation of their respective characters”.
The studies of Goddard are more thorough and scientifically more valuable because two lines from the same stock exhibit differences due to character and morality of two mothers. Yet the conclusion sought to be drawn almost entirely fails to take account of the environmental factors.
Esterbrook took up the thread of the history of Juke family where Dugdale had left it. He pushed his inquiries both further backwards and further forward. His studies are scientifically of great value because on the one hand, they confirm the general conclusions of Dugdale, yet clearly indicate the contribution of the environmental factor. Esterbrook’s researches revealed the fact that the cement works where a large number of Jukes worked had been closed.
After this the Jukes migrated to different States in search of employment. Some of them improved their economic condition and their social status also improved and they were enabled to marry into better families. The family history of these migrants brightened. There can be no doubt that the improved environment played a big part in the improvement of the Juke stock. But here also heredity in the shape of better hereditary stock of the girls who were married to the Juke boys, contributed largely.
“The blood of the better families has been the main cause of such permanents improvements as are now found in the Juke family. Dissemination has improved the Juke stock, but at a terrible expense to the communities into which they have migrated. The fact that so many of the 1,258 descendants living in 1915, found it impossible to adjust themselves socially to the new environments disposes of the claim that environment alone improves stock; the responses of the individual are also dependent upon his constitution.’
Galton examined the lives of famous scientists and as was to be expected, he concludes that their higher-than-average intelligence and achievements were definitely the result of heredity. But Cattell collected the life-history of eminent American scientists and came to an opposite conclusion. He said that there was a great disparity in the number of scientists in different regions. The density of population, favourable economic conditions, proper opportunities and proper arrangements for scientific training favour the appearance of eminent scientist.
Terman examined one thousand gifted children reading in colleges and universities, analysed their family history, economic conditions, and opportunities for scientific training and cast his vote in favour of heredity which he thinks is relatively more important. Opportunities often make a man. ‘Full many a gem of purest ray serene’ blush unseen because of lack of proper opportunities. The loving care of a wise mother or the encouragement of a good teacher has often been at the root of the extraordinary success of an ordinary man. On most men, environment in the shape of economic success and social status exerts a powerful influence. Most people are spoilt by power.
Even such trifling things as dress or weather either stimulate or depress a man and affect his behaviour. So far as social traits are concerned, environment exerts a more powerful influence than heredity. The study of twins has provided rich material in researches on heredity and environment. Twins are distinguished into identical twins and fraternal twins. Identical twins are due to the fertilisation of the same ovum and the early fission of the fertilised ovum; they have a common placenta and a common chorion (enclosing membrane). They are therefore genetically identical. They are always of the same sex and resemble each other very closely.
Fraternal twins are “really multiple births due to the fertilisation of two ova. They have two placentas and two chorions in embryo. There are really two separate births, though at the same time. Thus they are genetically like two siblings (brothers and sisters born of the same parents). Such twins also resemble each other, but not so closely as identical twins. Their resemblance generally is greater than that of ordinary siblings.
Many interesting and instructive studies of twins have been made. Of these the more important are by Galton, Thorndike, Merriman, and Lauterbach. More recent studies are those of Gesell and Thompson and the study of the five identical sisters (Diorme Quintuplets) currently published by Blatz. Almost all of them employed objective measurements and used the statistical device of correlation.
Psychologists are generally more interested in the problem of the degree of similarity or dissimilarity in intelligence between twins, siblings, near-related and unrelated individuals. Correlation simply means the degree of similarity. Higher correlation means a greater degree of similarity; a lower correlation a lesser degree of similarity.
As was to be expected, the degree of similarity in intelligence (as in other characteristics) is greater as the relationship is closer. Two identical twins show the highest correlation in the matter of intelligence; fraternal twins slightly less; siblings, still lesser.
The result is presented by Wingfield’ in the form of a table:
These studies reveal clearly the influence of heredity as also of environment. None can be ignored. The very high correlation of identical twins is due not only to identical heredity, but also because they are exposed to more nearly identical environmental influences than any other type of siblings. The correlation coefficient of unlike siblings can be explained by the fact that there is a traditional difference in training and play activities and the attitudes of parents and associates towards boys and girls.
Studies on Out-of-Society, A-Social and Anti-Social Individuals and Groups:
Feral cases are extremely rare, but they exhibit with painful vividity the adverse effect on a human child of total isolation from human society. The dependence of man’s human nature upon his membership in a society is supported by some evidence of a quasi-experimental kind.
It is, of course, hardly possible to make experiments by isolating infants from all social relationship, though certain absolute monarchs from King Psam-metichus of Egypt to James IV of Scotland and Akbar the Great are reported to have done so, always with adverse effects on the child.
“One of the most striking of these observations of what a human environment can do with an animal, concerns a baby chimpanzee (Gua) reared for about a year in a human home in the companionship of a boy (Donald) of about the same age. In this study of the ape and the child, there was a day-by-day record of the physical and social behaviour of the two, and experiments and films showing the great readiness of the baby chimpanzee to take on human ways, not only in posture and gesture, in the expression of affection but also in habits and skills up to a certain point.”
Of course, the physical development of the chimp was much faster but in mental development the human child soon outstripped the beast. But, the point is clear that an enriched environment does stimulate the growth of intelligence. But, of course, there are definite limits determined by heredity.
The effects of an impoverished, abnormal or vitiated environment show clearly in the children of gypsies, canal boatman who live almost their whole life on boats away from normal human habitations,—isolated communities living on inaccessible mountains or in deep forest regions, cut off from contact with civilized society. The studies of Gordon and Asher are revealing and instructive.
Children of such people are found to have a limited vocabulary and low intelligence. Children of nomadic criminal tribes are not only mentally retarded but grow up with criminal, anti-social attitudes and habits. The same is largely true of children brought up from infancy in vagrant homes and orphanages.
The effect of environment on the formation of habits and attitudes are often observable. Many Punjabi, Sindhi, Marwari and Biharis who have lived for more than one generation in Bengal, naturally learn the Bengali language and adopt many Bengalese habits and customs. Conversely, Bengalese families who made Bihar, Uttar Pradesh or Delhi their permanent habitat, generations ago, identified themselves with the people of those states, adopted their language, dress and food habits. Often their appearance also undergoes distinct changes. It would be wrong to attribute all these modification to environment alone.
“Much that is popularly attributed to heredity or to environment is really due to the interaction of the two. Thus most people will tell you that the short stature of the Japanese is simply a hereditary trait. Actually, Japanese reared on the Western coast of North America on average are three inches taller than Japanese reared in Japan; but even among the American-born Japanese a relatively shortness of stature prevails, with wide individual variability, of course, so that apparently both factors are involved.”
Children (particularly twins) Reared Apart:
Foster children (particularly one of co-twins) as also orphans provide a special opportunity to isolate, to a certain extent, the influence of heredity from that of environment, because such children lose contact with parents or other persons related to them by heredity. Here one of the co-twins grows up in his natural home, whereas the other one grows up in a foster family.
This is a sort of social experiment, though it is not intended as such. Here the child living with his natural family acts as a ‘control’ against which the influence of the new environment may be assessed. This influence is most clearly noticeable in case where the child had been adopted into the foster family when it is only an infant. When a child above five years is adopted in a strange foster-home, he shows an initial period of fretting and tension due to the difficult process of adjustment to an entirely new family environment.
The most important studies in this respect are those carried on by Miss Barbara Burks who examined 204 children and compared them with the intelligence, physical health and social traits of their natural parents and foster parents.
In 1932 Leahy conducted a similar study in Minnesota. Both of them admit that there is a distinct improvement, at least in social qualities if the foster-home is culturally superior to their original homes. But they take pains to emphasise the importance of heredity by pointing out that the correlation co-efficient in matters of intelligence, home influence etc. between the child and his natural parents is consistently higher than those between the child and his foster parents.
Newman, Freeman and Holzinger also undertook a detailed study of twins in differing environments and concluded that though hereditary similarities persist throughout, foster-children, nevertheless, show a rise in I.Q. after adoption into a foster home, if, as often happens, the foster-home is socially and culturally superior. The rise is greater the younger the child at the time of adoption and the higher the socio-economic level of the foster-home.
Essay on Heredity # Studies of Infants under Different Cultural Conditions:
Dennis who made a study of infant behaviour under different cultural condition is more emphatic than Burks & Leahy in their underestimation of the influence of the environment. “He has given us good evidence that the development of bodily functions such as the ability to stand and to walk, is not much affected during the first year of life even by wide extreme of environment.”
Gesell also stresses this point—that the process of maturation is almost entirely independent of the environment. Dennis also offered evidence that many phases of social growth go on during the first year of life, independently of the family or social environment. Smiling, cooing, laughing etc. do not seem to be retarded by their isolation from or change of the social environment.
Wellman’s and Rene Spitz’s studies, however, seem to lead us to an opposite conclusion. Spitz’s observations show that the presence and attitude of the mother make a huge difference in objectively observable development in social characteristics as revealed in a series of responses to standardized social situations.
He conclusively shows that children who lost their mother in early infancy or were deserted by her and almost invariably all children reared up in institutions like foundling homes show signs of retardation not only in social responses but in such physical attributes such as standing, clinging while standing, walking etc.’
The conclusion though based on conflicting evidence is broadly that so far as the development of the basic physical behaviour is concerned, heredity is the more important factor, though even here, environmental influence cannot be altogether ignored. So far as the social-emotional responses and tastes and attitudes are concerned, they are largely determined by environmental factors.
Correlation of the Intelligence of Foster Parents and Foster Children:
Many studies on foster children and their correlation in the matter of intelligence with their natural siblings and foster siblings or foster parents bring out the inescapable hereditary influence. Studies on illegitimate children placed in an orphanage under the age of one year and moved there together without home contacts also bring out significantly the importance of the hereditary factor.
Such children developed large differences in intelligence with high significant correlation with the socio-economic level of their own parents. “Orphans of merchants and professional men, for example scored on the average about 10 points higher in I.Q. than the orphan of labourers in the same institution.”
This emphasises the influence of heredity. But the pre-natal care in the case of these children must have been responsible to a certain extent in affecting health, stamina, physical vigour and other characteristics and influencing intelligence in an indirect way.
Effect of Parents’ Socio-Economic and Occupational Status:
Many studies reveal a high degree of correlation between the occupational status of the father and the I.Q. and cultural index score of their children.
The following table from Haggerty and Nash summarizes the result of the inquiry:
The association between the father’s occupational level and children’s I.Q. in itself could be interpreted as the result of either hereditary or environmental influences or both. Thus it might be argued that the brighter fathers are more likely to have brighter children. On the other hand, the superior home environment furnished by fathers in the higher occupational levels may have determined the higher I.Q.’s of the children in these levels.
Essay on Heredity # Certain Experiments on Heredity and Environment:
Experiment requires keeping constant all other factors and changing only one of the variables. In most experiments attempt is made to modify heredity through some change in the environment. Agriculturists and animal-breeders have from time immemorial tried to create new varieties by controlling environmental factors like food, temperature, light, water etc.
They have often succeeded in creating new and better varieties—new varieties of roses, dahlias, chrysanthemums and new varieties of dogs, sheep and cows by cross-fertilisation or by controlling some environmental factor. The Russian agro scientists Lysenko and Michurin claimed to have produced new varieties of wheat which yield faster and better quality grains by the process of vernalisation (when the seeds are subjected to sudden massive drop in temperature for a prolonged period).
Russian scientists under the Stalinist regime claimed that environment is everything and heredity can be suitably modified through controlling the environment. The tall claim has not been accepted by scientists working in-this field in other countries.
Now, however, after the discovery of the structure of the DNA molecule, attempts are vigorously being made to produce new species by changing the structure of this molecule. This opens up an exciting possibility though as yet complete success has eluded the efforts.
Fiction writers have been fascinated by this idea as evident by Mrs. Shelley’s Frankenstein, Aldous Huxley’s The Brave New World, Bernard Shaw’s Pygmalion and George Orwell’s Nineteen Eighty-four. But a moderate amount of success has attended the efforts of scientists to change the nature of an animal by changing the secretion of the hormones from the ductless glands.
Are Acquired Characteristics Transmissible?
These experiments suggest that though, generally, acquired characteristics are not transmissible, at least in higher animals, it may be possible to transmit within a narrow limit, some secondary characteristics. So far as the primary characteristics of a species are concerned, heredity cannot be controlled.
Final Assessment:
We find the scientific mass of evidence collected through controlled observation and experiment lead to conflicting conclusions. Some emphasise heredity, others stress the contribution of environment. Some say that by keeping heredity constant and changing the environment, there are significant changes; others say that the changes in the environment have only a marginal effect on heredity. Again, by keeping the environment constant and changing the heredity we sometimes find a large amount of uniformity and sometimes we get an opposite result.
Sometimes acquired characteristics seemed to be not transmissible; sometimes it seems that by selective breeding, acquired characteristics are transmissible. Do we then face a hopeless contradiction in the facts? “Not necessarily. Perhaps we have been like the three blind men who argued whether the elephant was trunk, legs or tail; each has been grasping one aspect, and a perfectly good and real aspect of the problem, but leaving out other aspects. There is an inner dynamic growth process; and it is shaped by the environment.”
Probably the way in which heredity and environment interact varies with the process we are observing. It is not a question of the ‘environment’ in the abstract, and ‘heredity’ in the abstract. Every one of us react differently to our environment. Some aspects of a given environment help some individual in some specific ways, not necessarily in other ways. What is innate and hereditary to an individual is revealed under the impact of a particular environment.
One thing is certain that heredity and environment interact. One cannot be understood, apart from the other. The idea of a “good heredity” is then an abstraction. So is the idea of a “good environment”. Beyond a certain point, these observations are not very helpful. We must understand how on a particular individual, in a particular situation they interact. The pattern of interaction is unique in each individual. So it is often dangerous to generalize and dogmatise.’
Certain General Conclusions However, Seem to be Firmly Indicated:
(a) In general, and in particular cases both heredity and environment play their part. “There is no item of the behaviour repertoire, no intellectual trait nor personality characteristic that is wholly independent of the genes of its possessors or of the events which have altered him since he began living.”
(b) There is general agreement on the question of this interaction. But controversies arise regarding the contribution of each factor in general and in particular cases. “It is the degree to which any one aspect of behaviour depends upon structural limitations traceable to heredity and, the degree to which it depends upon the accumulated effects of environment: that is the area of controversy.”
(c) “In the development of motor and sensory capacities, the role of hereditary factors is commonly emphasised … The close dependence of motor and sensory functions upon physical structures makes such functions more directly susceptible to hereditary determination although both capacities depend, in part, on environmental influences. In intellectual functions, extreme deviations in either direction from the norm often reflect, in part, the influence of health, stamina, endurance, glandular activity or pathological conditions which make normal intellectual development impossible.”
These, of course, depend largely on heredity. Within the broad range of intermediate deviations, the range which includes most persons, the role of heredity is much less apparent. It is with regard to such minor intellectual functions that one finds the greatest divergence of opinion among psychologists. In respect of emotional and social characteristics, attitudes, moral standards and other aspects of personality, most psychologists recognize a major contribution by environmental factors.
Essay on Heredity # What Hope for Humanity?
The prospect and possibility of improving the human race has proved a fascinating idea for enthusiastic idealists, politicians, social workers and educationists. The science of eugenics dreams of improving the human race through the control of food, hormone secretions, therapeutic measures, selective breeding etc. The ambitious politician takes positive steps to produce mass-obedience to certain ideologies through intensive propaganda and indoctrination.
The social reformer seeks to change humanity through better education in the ideas of social justice etc.; the psychologists are hopeful that with a more perfect knowledge of the laws of learning, motivation, attention etc. and with the help of the intelligence and other kinds of standardized tests it might be possible to teach men to become better. The Pavlovians would pin their faith in the conditioned reflex.
The Freudians believed that through psychoanalysis and the control of the unconscious mind, and through suggestions it might be possible to get the right kind of men. “Actually what we are after, is knowledge of how to change people, knowledge of how much they can be changed. The solutions of all great social problems, all social progress, depend on that.”
Heredity does act as a limiting force. The barrier must be recognised and it would be futile to attempt the impossible. The complete control of heredity through the improvement of the environment is yet a distant dream. Moreover, what is possible is to seek to improve the individual by providing healthier and more stimulating environmental situations.
But this improvement of the individual may not be transmitted through heredity to later generations. So the educationists have no scope for relaxation. But there is also compensation in the knowledge that acquired characteristics may not be transmitted, because if good taste and skills are not hereditary, drunkenness, delinquency and (most) diseases are not hereditary.
Moreover, if the general level of intelligence and performance of a particular generation may be improved by 5 points that is a great social gain and this gain would be indirectly carried over to the new generations through ‘social heredity’ which is not an empty concept.’ The children of intelligent and well-adjusted parents have a better start in life, and the number of such children should be increased—certainly not allowed to decrease.
The next generation has a just claim on the present generation to provide it with the best parents possible. Of course, it is up to us to improve the environmental conditions and opportunities for self-development of our children, because in this lies our reasonable hope for their improvement—whatever be their heredity.