Resources for Communication Problems

Sunday, February 3, 2008




(b) Relevance of the History of the Skull. Could the palaeontological history of the human skull give us clues about the emergence of language? Critical evaluation of the evidence speaks against this. Instead of brains from fossil men, we have only an array of skull fragments. From these fragments, endocasts are made, that is, plaster-casts of the concavities. Unfortunately, the patterns of cortical sulci are not well-delineated on the calvarium. The main landmarks inside the extant bones are the meningeal vessels which, in modern man, do not bear a constant relationship to fissures and sulci of the sub-pial cortical surface. Thus, endocasts give no language-relevant information. They tell us something about the brain’s approximate size and shape, but nothing about cortical fields, subcortical connections, or other internal structure.

If a group of experts were handed fragments of the crainum (or the entire exenterated skull, for that matter) of mosern man, say an individual who died three years before under unknown circumstances, and were asked to say whether or not that person had acquired language, they could only give an answer in terms of statistical probabilities, namely the incidence of persons who do and who do not have language in the presence of normal bone formation. Their judgment would be based entirely on their knowledge of conditions prevailing today among the population at large. The bones themselves could give them no clue as to the language capacities of the deceased. He might have been a normocephalic retardate or a great orator, or, if the skull is subnormally small, it might have belonged to an African pygmy or a birdheaded dwarf-in either case in possession of language-or it might have been a microcephalic individual with no more than a few words at his command. If one cannot make unfailing deductions from recent bones, one can hardly presume that inferences are possible about fossil men who lived under almost totally unknown circumstances.

The extraordinary size of modern man’s brain and the cause of its relatively rapid phylogenetic development have captured the imagination of virtually every student of human descent. This evolutionary event has been generally linked to our capacity for language. Although I tend to be skeptical about this relationship, based on the evidence mentioned elsewhere, I admit that there can be no proof for the historical independence of brain size and language.

The oldest fossil which some authorities are willing to regard as the first human ancestor is Australopithecus who lived one to two million years ago ( there is considerable uncertainty about the age). His brain was about as large as that of a modern gorilla, but he was slighter in build than the modern ape, so that he might have had a relatively large brain. If we are right in classifying him into a family distinct from the Pongidae (chimpanzee, gorilla, orangutang), we must also accord him some peculiar brain functions. If the modern apes do not talk, this is no evidence against the possibility that Australopithecus had some potential for a primitive form of speech-like communication. A study of his skull cannot decide the question. Later, more distinctly hominid fossils, such as Java man and Peking man, had successively larger cranial capacities. Toward the end of the third glacial, fairly suddenly, a new race appeared with brains as large as ours: Neanderthal man. It appears to be the consensus today that this form was a racial specialization that became extinct without affecting the ancestorial line from which we have come. Our direct forebears, the Cro-Magnon race, emerged about fifty thousand years ago. Their brains had the same size as Neanderthal’s; in fact, on the average, the cranial capacity was slightly larger than that of modern man. Cro-Magnon’s skull had one characteristic in which it differed from all other types of human fossils: its shape. The skull was shorter but higher, and there was a forward shift of its center of gravity; it was balanced differently on the spinal column.

Haldane (1949) and Mayt (1963) have pointed out that the rise of modern man, particularly the increase in cranial capacity, has occurred within a spectacularly short period. Although evolutionary changes are often measured in terms of millions of years and a time-span of a hundred thousand years. We may wish to speculate on the target of the selection pressures at work. What was so advantageous about a large brain and skull?

It is tempting to relate the size of the brain to man’s two most outstanding characteristics: his capacity for language and his general cognitive capacities. Intuitively, this relation may be reasonable. But it is important to remember that it rests on no more than just that: intuition. There is no way of demonstrating that cognitive or language capacities either required or resulted from a rapid increase in the number of brain cells.

One common line of argument in favor of relating brain size to intelligence and language is based on observations of feeble-minded individuals. In this case, it is not uncommon that abnormally small brains are correlated with a lowering of intellect, and language learning ability may be affected also. However, feeble-minded patients are not replicas of primitive human races; they are not a viable subspecies. Their constitution and growth patterns are deeply abnormal; their brain functions have not developed properly, and little is known about the quantitative aspects of their brain-cell populations. These deviants can tell us nothing about evolutionary history of the brain.

There is, however, another line of argument that induces many scholars tp suspect a close relationship between brain size and intelligence. It is based on purely logical considerations; in fact, the reasoning underlying it is by analogy. The capacities of an electronic computer or desk calculator are directly related to the number of its constituent elements. This engenders the belief that an increase in the number of units in the brain has a similar consequence. However, evidence for this is surprisingly poor. Perhaps Lashley’s early observations might be cited in support of this contention, namely that the quantity of cerebrocortical destruction is capable of. But it is not clear hoe these studies relate to human intelligence. For instance, Teuber (1959) and Ghent, Mishkin, and Teuber (1962) have compared intelligence test scores of war veterans at the time of their recruitment with scores on the same test several years later and after extensive brain injures; there was no significant difference between before and after cortical destructions. Nor did short term memory change as a consequence of frontal-lobe tissue destruction.

If the increase in neuronal elements did bring about an increase in capacity (and this remains a reasonable assumption), we are still incapable of defining capacity. There is no clear indication whether it is related to storage, to simultaneous processing, to internal efficiency of processing, to more advantageous utilization of input, or to speeding up of processing time, etc. we do not know how any of these purely theoretical aspects of capacity are related to particular quantitative dimensions such as brain weight, cell counts, and neurodensity. It is not good enough to say, “there is nothing else that a large brain could be good for than to bring about greater intelligence and language!” This is merely a reflection of our ignorance on the causes of particular evolutionary changes.

Since this point is pf no small consequence for our image pf man, his capacities, and his place in the primate order, one last consideration on the nature of cognition may be in order. Suppose we explore cognitive capacities of animals and man by systematic measurements of a great number of aspects of psychological activities. Let it include various types of memory, of pattern recognition, of associative capacities, of generalization, and propensity for inference. Each type of measurement constitutes a dimension with which we can construct a multidimensional, mathematical space; let us call it the generalized cognition-space. The total capacities that characterize a given species, that is, its species-specific cognition, becomes now a locus in the cognition-space. Cognitive evolution could be expressed, in such a space, as vectors; the locus of an earlier form is thus connected with that of a later form. The directionality and length of the vector represent the peculiar changes that took place in the course of evolution to bring about the species-specific cognition of a given animal. In terms of this conceptualization, could we expect all evolutionary cognitive changes to be vectors that have the same direction? Such a supposition seems absurd. On the other hand, the enlargement of the brain is a widespread and recurring phenomenon. It appears to be contrary to our empirical findings that an increase in size changes cognitive capacity into a specific direction. Thus, man’s peculiar type of intelligence is not the “logical or necessary” outcome of the enormous growth of his brain, and his capacities today could not have been predicted simply from a knowledge of the evolutionary trend of the change of brain-volume.

In short, we do not know why the brain increased so rapidly in size. Since man is distinct from other hominidae in many ways, we cannot reconstruct which feature added most to selection pressures and which came about through pleiotropic effects (Caspari, 1958). Although it is entirely possible that the emergence of language and intelligence are historically related to the increase in size of the brain, the case is certainly not yet irrefutably proven, and the various arguments adduced for one or the other position are too weak to allow us to date the onset of language from fossil remains.

我所分配到的文章部分的大綱是在提頭骨對人類的影響,人的頭骨的古生物學歷史能給我們線索關於語言誕生嗎? 證據性的重要評估對這個問題提出反對。主要地標在現存骨頭,因而, endocasts 不提供語言相關的資訊。他們告訴我們某事關於腦子的近似大小和形狀。他們的評斷整個地會根據情況,骨頭不能給他們線索至於逝者的語言容量。如果你無法由最近骨頭做unfailing 扣除, 你可能幾乎不假定, 推斷是可能的關於在幾乎完全未知的情況下居住的化石人。現代人的腦子的非凡大小和它的相對地迅速種系發生的發展的起因捕捉了實際上每名學生的想像力。這次演變事件與我們的容量一般連接了為語言。雖然作這傾向於是懷疑的關於這個關係, 根據證據在別處被提及,那裡可能是沒有證明為腦子大小和語言的歷史獨立。一些當局是願意看待的最舊的化石因為第一人的祖先是居住一到二百萬年前的Australopithecus (那裡是可觀的不確定性關於年齡)如果現代猿不談話, 這是沒有證據反對可能性, Australopithecus 有在講話像通信的一個原始形式的一些潛力。他的頭骨的研究無法決定問題。以後, 更加分明地原始人類的化石, 譬如Java 人和北京人, 有連續地更大的頭蓋骨容量。Cro Magnon 種族, 湧現大約五萬年前。他們的腦子有相同大小像Neanderthal ; 實際上, 在平均, 頭蓋骨容量比那輕微地大的現代人。

CroMagnon's 頭骨有它與所有其它類型人的化石不同的一個特徵: 它的形狀。頭骨是更短的但更高, 並且有它的重心一個向前轉移; 它不同地平衡了在脊柱。Haldane (1949) 並且Mayt (1963) 指出, 現代人的上升, 特殊在頭蓋骨容量的增量, 發生在一個短期間內。雖然演變變動經常被測量根據成千上萬幾年和一十萬年的時間間距。我們也許希望推測在選擇壓力的目標在工作。什麼是很有利的關於一塊大腦子和頭骨?

它誘惑與人的兩個最卓著的特徵關係腦子的大小: 他的容量為語言和他的一般認知容量。直覺地, 這聯繫也許是合理的。沒有方式顯示出, 認知或語言容量或必需或起因於在腦細胞的數量的迅速增量。一個共同的自變量範圍傾向於關係腦子大小與智力和語言根據低能個體的觀察。在這種情況下, 它不是不凡的, 反常地小腦子被關聯以降下智力, 並且語言學習能力也許並且影響。但是, 低能患者不是原始人種複製品; 他們不是一個可實行的亞種。這些異常可能告訴我們什麼關於腦子的演變歷史。然而, 導致許多學者懷疑在腦子大小和智力之間的其它自變量範圍有密切的關係。它根據純淨地邏輯考慮; 實際上, 推理部下它是由比喻一個電腦或書桌計算器的容量直接地與它的構成元素有關的數量。這造成信仰, 在單位的數量的增量在腦子有相似的後果。簡而言之, 我們不知道為什麼腦子那麼迅速地增加了在大小。因為人是分明從其它hominidae 用許多方式, 我們無法重建特點增加多數來選擇壓力並且出現通過pleiotropic 作用(Caspari 1958) 。雖然它是整個地可能的語言誕生和智力歷史上與在腦子的大小的增量有關, 案件無可辯駁地一定不被證明, 並且各種各樣的論據舉例為一個或其它位置太微弱的以至於不能迄今給我們語言起始從化石遺骸的。

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