Adapted from Darwinism by Alfred Russel Wallace (1889)

Everyone knows that in each litter of kittens or of puppies no two are alike. Even in the case in which several are exactly alike in colors, other differences are always perceptible to those who observe them closely. They will differ in size, in the proportions of their bodies and limbs, and in the length or texture of their hairy covering. They each possess, too, an individual countenance; we all know that each kitten in the successive families of our old favorite cat has a face of its own, distinct from all its brothers and sisters. Now this individual variability exists among all creatures that we can closely observe, even when the two parents are very much alike and have been matched in order to preserve some special breed. The same thing occurs in the vegetable kingdom. All plants raised from seed differ more or less from each other. In every bed of flowers or of vegetables we shall find, if we look closely, that there are countless small differences, in the size, in the mode of growth, in the shape or color of the leaves, in the form, color, or markings of the flowers, or in the size, form, color, or flavor of the fruit. These differences are usually small, but are yet easily seen, and in their extremes are very considerable; and some of these differences have this important quality, that they have a tendency to be reproduced, and thus by careful breeding certain particular variations or groups of variations can be increased to an enormous extent—apparently to any extent not incompatible with the life, growth, and reproduction of the plant or animal.

The way this is done is by artificial selection, and it is very important to understand this process and its results. Suppose we have a plant with a small edible seed, and we want to increase the size of that seed. Suppose also that the maximum size of a seed of this type of plant is solely dependent on the maximum sizes of the seeds of its parents. We grow as large a quantity of it as possible, and when the crop is ripe we carefully choose a few of the very largest seeds, or we may by means of a sieve sort out a quantity of the largest seeds. Next year we sow only these large seeds, taking care to give them suitable soil and manure, and the result is found to be that the average size of the seeds is larger than in the first crop, and that the largest seeds are now somewhat larger and more numerous. Again sowing these, we obtain a further slight increase of size, and in a very few years we obtain a greatly improved type that will always produce larger seeds than the unaltered type, even if cultivated without any special care. In this way all our fine sorts of cultivated vegetables, fruits, and flowers have been obtained, all our choice breeds of cattle or of poultry, our wonderful racehorses, and our endless varieties of dogs. It is a very common but mistaken idea that this improvement is due to crossing and feeding in the case of animals, and to improved cultivation in the case of plants. Crossing is occasionally used in order to obtain a combination of qualities found in two distinct breeds, and also because it is found to increase the constitutional vigor; but every breed is the result of the selection of variations occurring year after year and accumulated in the manner just described. Repeated selection in favor of certain traits is the foundation of all of the controlled changes made in our breeds of domestic animals and strains of cultivated plants.

Which of the following statements, if true, would weaken the author's overall argument?

Adapted from Are the Planets Inhabited? by E. Walter Maunder (1913)

What is a living organism? A living organism is such that, though it is continually changing its substance, its identity, as a whole, remains essentially the same. This definition is incomplete, but it gives us a first essential approximation, it indicates the continuance of the whole, with the unceasing change of the details. Were this definition complete, a river would furnish us with a perfect example of a living organism, because, while the river remains, the individual drops of water are continually changing. There is then something more in the living organism than the continuity of the whole, with the change of the details.

An analogy, given by Max Verworn, carries us a step further. He likens life to a flame, and takes a gas flame with its butterfly shape as a particularly appropriate illustration. Here the shape of the flame remains constant, even in its details. Immediately above the burner, at the base of the flame, there is a completely dark space; surrounding this, a bluish zone that is faintly luminous; and beyond this again, the broad spread of the two wings that are brightly luminous. The flame, like the river, preserves its identity of form, while its constituent details—the gases that feed it—are in continual change. But there is not only a change of material in the flame; there is a change of condition. Everywhere the gas from the burner is entering into energetic combination with the oxygen of the air, with evolution of light and heat. There is change in the constituent particles as well as change of the constituent particles; there is more than the mere flux of material through the form; there is change of the material, and in the process of that change energy is developed.

A steam-engine may afford us a third illustration. Here fresh material is continually being introduced into the engine there to suffer change. Part is supplied as fuel to the fire there to maintain the temperature of the engine; so far the illustration is analogous to that of the gas flame. But the engine carries us a step further, for part of the material supplied to it is water, which is converted into steam by the heat of the fire, and from the expansion of the steam the energy sought from the machine is derived. Here again we have change in the material with development of energy; but there is not only work done in the subject, there is work done by it.

But the living organism differs from artificial machines in that, of itself and by itself, it is continuously drawing into itself non-living matter, converting it into an integral part of the organism, and so endowing it with the qualities of life. And from this non-living matter it derives fresh energy for the carrying on of the life of the organism.

Which of the following statements, if true, would most weaken the passage's argument?

Adapted from On the Origin of Species by Charles Darwin (1859)

The many slight differences which appear in the offspring from the same parents, or which it may be presumed have thus arisen, from being observed in the individuals of the same species inhabiting the same confined locality, may be called individual differences. No one supposes that all the individuals of the same species are cast in the same actual mold. These individual differences are of the highest importance for us, for they are often inherited, as must be familiar to every one; and they thus afford materials for natural selection to act on and accumulate, in the same manner as man accumulates in any given direction individual differences in his domesticated productions. These individual differences generally affect what naturalists consider unimportant parts; but I could show, by a long catalogue of facts, that parts which must be called important, whether viewed under a physiological or classificatory point of view, sometimes vary in the individuals of the same species. I am convinced that the most experienced naturalist would be surprised at the number of the cases of variability, even in important parts of structure, which he could collect on good authority, as I have collected, during a course of years. It should be remembered that systematists are far from being pleased at finding variability in important characters, and that there are not many men who will laboriously examine internal and important organs, and compare them in many specimens of the same species. It would never have been expected that the branching of the main nerves close to the great central ganglion of an insect would have been variable in the same species; it might have been thought that changes of this nature could have been effected only by slow degrees; yet Sir J. Lubbock has shown a degree of variability in these main nerves in Coccus, which may almost be compared to the irregular branching of the stem of a tree. This philosophical naturalist, I may add, has also shown that the muscles in the larvæ of certain insects are far from uniform. Authors sometimes argue in a circle when they state that important organs never vary; for these same authors practically rank those parts as important (as some few naturalists have honestly confessed) which do not vary; and, under this point of view, no instance will ever be found of an important part varying; but under any other point of view many instances assuredly can be given.

Which of the following statements, if true, would most seriously weaken the author's argument?

"Evolution" by William Floyd (2015)

The term “human evolution” brings to mind one long smooth transition, with the human race having gone neatly from Homo habilis to Homo erectus to Homo neanderthalis and on through to the present day Homo sapiens. Lining up all of the ancestors of modern humans in front of the outline of Homo sapiens can be a convenient teaching tool in elementary and middle school classrooms, but it greatly distorts the actual course of human evolution. One human species did not simply pick up the baton of the evolutionary relay from a dying ancestor, becoming the only true hominid walking the earth. Our evolutionary ancestors were actually competing with one another for their survival, coexisting warily throughout a relatively recent period of the earth’s history.

Neanderthal has become an insult to be hurled toward a crude or unsophisticated person, but the actual Neanderthals were relatively sophisticated. Homo neanderthalis was notably larger than Homo sapiens, hunted a wide variety of animals, and spread throughout harsher climates than their hominid relatives. In fact, in many parts of modern day Europe, the remarkable dominance of Homo neanderthalis in the archaeological record shows they were the main force in Europe for tens of thousands of years. More notably, for the 5,000 years that Neanderthals shared Europe with Homo sapiens, Neanderthals were the larger presence across the continent with more tools, homesites, and burials of Neanderthals existing from the short period. There is essentially no evidence that what we think of as the “modern human” was the most perfectly adapted hominid to the world of 40,000 years ago.

The Homo sapiens, of course, eventually won out, although scientists disagree about what made the Neanderthals become permanently etched in history rather than the present. For a long time, the popular opinion was that bloody conflict between humans and Neanderthals was in the end decisively won by humans, resulting in the permanent extinction of Neanderthals from the earth. However, recent studies of Neanderthal DNA extracted from very old remains have delivered some results which shatter a notion of modern humans having demolished any trace of Neanderthals. Actually, modern humans have a significant trace of Neanderthals living within them, as a large share of the human genome contains remarkable similarities to Neanderthal DNA. Quite likely, Homo sapiens did not take over from Homo neanderthalis as the chief hominid on the planet, but in fact coexisted to the point of absorbing Neanderthals into human society and DNA.

Which of the following statements would most strengthen the argument presented in the passage?

"Darwin and Wallace" (2016)

Alfred Russel Wallace developed what he termed “the tendency of varieties to depart from the original type” while on an extended research trip in Borneo. During earlier research in the Amazon basin, Wallace had observed that certain, highly similar species were often separated by a small distance, but some type of significant geographical barrier. Although he was halfway around the world, Wallace was keeping in touch with fellow scientists in his native Britain, including Charles Darwin, who was most notable at that time for a large book on barnacles and his trip around the world on the HMS Beagle over a decade and a half earlier.

When Wallace sent Darwin a letter in February of 1858, Wallace’s intention was merely to ask if his findings in Malaysia were consistent with Darwin’s private theorizing about the development of species. Darwin received the letter in June, and was astonished at what he read from Wallace. He fired off a letter to Charles Lyell, head of the prestigious scientific organization the Linnean Society. Lyell had previously expressed concern that Darwin’s long gestating theory of natural selection would be preempted by another researcher, expressing a strong likelihood it would be Wallace.

The custom among scientists at the time called for the first person to publish a theory to be given credit for it. Wallace was well on his way to publishing his own work, largely in the form of the letter he had sent Darwin. Lyell, who had been hearing about Darwin’s theory for fifteen years, believed that both men should receive some credit. With his position of authority at the Linnean Society, Lyell arranged to have a joint paper read at the last meeting before their summer break in 1858, which took place on the first of July. The meeting was relatively well attended for the time, with over thirty people in the audience, including two foreigners. The vast majority of them were there to hear a eulogy for Robert Brown, the Scottish botanist and former president of the Society, who had passed away in early June.

Neither Alfred Russell Wallace nor Charles Darwin were present at the meeting. Wallace was still in Southeast Asia, totally unaware that the joint paper was being presented, only being informed by a letter after the meeting. Darwin was in his native Kent, far away from London, burying his recently deceased baby son, Charles Waring Darwin, who had succumbed to scarlet fever just three days previously. Darwin gave Lyell and fellow scientist Robert Hooker Wallace’s letter, a letter he had written to the American researcher Asa Gray, and an essay he had written in 1844. He then told Lyell and Hooker that he was unable to attend.

Little was made of the joint reading. Only a few small reviews were made, none of which either greatly lauded or fiercely criticized the theory of natural selection. After this, Darwin left his home with his family, seeking to get away from the disease that killed his youngest child, and began a large book on the theory. Wallace kept traveling across the Malay Archipelago, finding new evidence for the theory everywhere he went.

Charles Darwin’s name would become indelibly linked with natural selection; in particular, its subsequent overarching idea of the evolution of human beings due to the big book he was writing, On the Origin of Species. Its publication in 1859 would revolutionize how scientists thought about natural history, biology, and even science’s relation to religion. Darwin would often retreat from public scrutiny and engagement. In his stead, it was often Alfred Russell Wallace, who had returned to England in 1862, defending what became known as “Darwin’s theory.” Wallace’s significant contribution to natural selection was recognized by scientists, but rarely by the public. Nonetheless, from prompting the initial publication of the idea to staunchly fighting for it, Alfred Russell Wallace was key to the development of evolution.

Which of the following statements, if true, would most strengthen the argument presented in the passage?

"Evolution" by William Floyd (2015)

The term “human evolution” brings to mind one long smooth transition, with the human race having gone neatly from Homo habilis to Homo erectus to Homo neanderthalis and on through to the present day Homo sapiens. Lining up all of the ancestors of modern humans in front of the outline of Homo sapiens can be a convenient teaching tool in elementary and middle school classrooms, but it greatly distorts the actual course of human evolution. One human species did not simply pick up the baton of the evolutionary relay from a dying ancestor, becoming the only true hominid walking the earth. Our evolutionary ancestors were actually competing with one another for their survival, coexisting warily throughout a relatively recent period of the earth’s history.

Neanderthal has become an insult to be hurled toward a crude or unsophisticated person, but the actual Neanderthals were relatively sophisticated. Homo neanderthalis was notably larger than Homo sapiens, hunted a wide variety of animals, and spread throughout harsher climates than their hominid relatives. In fact, in many parts of modern day Europe, the remarkable dominance of Homo neanderthalis in the archaeological record shows they were the main force in Europe for tens of thousands of years. More notably, for the 5,000 years that Neanderthals shared Europe with Homo sapiens, Neanderthals were the larger presence across the continent with more tools, homesites, and burials of Neanderthals existing from the short period. There is essentially no evidence that what we think of as the “modern human” was the most perfectly adapted hominid to the world of 40,000 years ago.

The Homo sapiens, of course, eventually won out, although scientists disagree about what made the Neanderthals become permanently etched in history rather than the present. For a long time, the popular opinion was that bloody conflict between humans and Neanderthals was in the end decisively won by humans, resulting in the permanent extinction of Neanderthals from the earth. However, recent studies of Neanderthal DNA extracted from very old remains have delivered some results which shatter a notion of modern humans having demolished any trace of Neanderthals. Actually, modern humans have a significant trace of Neanderthals living within them, as a large share of the human genome contains remarkable similarities to Neanderthal DNA. Quite likely, Homo sapiens did not take over from Homo neanderthalis as the chief hominid on the planet, but in fact coexisted to the point of absorbing Neanderthals into human society and DNA.

The effect of a scientific study showing Homo neanderthalis and Homo sapiens never lived in close proximity on the author's argument would be __________.

"Darwin and Wallace" (2016)

Alfred Russel Wallace developed what he termed “the tendency of varieties to depart from the original type” while on an extended research trip in Borneo. During earlier research in the Amazon basin, Wallace had observed that certain, highly similar species were often separated by a small distance, but some type of significant geographical barrier. Although he was halfway around the world, Wallace was keeping in touch with fellow scientists in his native Britain, including Charles Darwin, who was most notable at that time for a large book on barnacles and his trip around the world on the HMS Beagle over a decade and a half earlier.

When Wallace sent Darwin a letter in February of 1858, Wallace’s intention was merely to ask if his findings in Malaysia were consistent with Darwin’s private theorizing about the development of species. Darwin received the letter in June, and was astonished at what he read from Wallace. He fired off a letter to Charles Lyell, head of the prestigious scientific organization the Linnean Society. Lyell had previously expressed concern that Darwin’s long gestating theory of natural selection would be preempted by another researcher, expressing a strong likelihood it would be Wallace.

The custom among scientists at the time called for the first person to publish a theory to be given credit for it. Wallace was well on his way to publishing his own work, largely in the form of the letter he had sent Darwin. Lyell, who had been hearing about Darwin’s theory for fifteen years, believed that both men should receive some credit. With his position of authority at the Linnean Society, Lyell arranged to have a joint paper read at the last meeting before their summer break in 1858, which took place on the first of July. The meeting was relatively well attended for the time, with over thirty people in the audience, including two foreigners. The vast majority of them were there to hear a eulogy for Robert Brown, the Scottish botanist and former president of the Society, who had passed away in early June.

Neither Alfred Russell Wallace nor Charles Darwin were present at the meeting. Wallace was still in Southeast Asia, totally unaware that the joint paper was being presented, only being informed by a letter after the meeting. Darwin was in his native Kent, far away from London, burying his recently deceased baby son, Charles Waring Darwin, who had succumbed to scarlet fever just three days previously. Darwin gave Lyell and fellow scientist Robert Hooker Wallace’s letter, a letter he had written to the American researcher Asa Gray, and an essay he had written in 1844. He then told Lyell and Hooker that he was unable to attend.

Little was made of the joint reading. Only a few small reviews were made, none of which either greatly lauded or fiercely criticized the theory of natural selection. After this, Darwin left his home with his family, seeking to get away from the disease that killed his youngest child, and began a large book on the theory. Wallace kept traveling across the Malay Archipelago, finding new evidence for the theory everywhere he went.

Charles Darwin’s name would become indelibly linked with natural selection; in particular, its subsequent overarching idea of the evolution of human beings due to the big book he was writing, On the Origin of Species. Its publication in 1859 would revolutionize how scientists thought about natural history, biology, and even science’s relation to religion. Darwin would often retreat from public scrutiny and engagement. In his stead, it was often Alfred Russell Wallace, who had returned to England in 1862, defending what became known as “Darwin’s theory.” Wallace’s significant contribution to natural selection was recognized by scientists, but rarely by the public. Nonetheless, from prompting the initial publication of the idea to staunchly fighting for it, Alfred Russell Wallace was key to the development of evolution.

What would be the chief effect of information that a scientist had developed the theory of natural selection fifty years before the work of Alfred Rusell Wallace or Charles Darwin, and that both men had read this research?

Adapted from Are the Planets Inhabited? by E. Walter Maunder (1913)

The first thought that men had concerning the heavenly bodies was an obvious one: they were lights. There was a greater light to rule the day, a lesser light to rule the night, and there were the stars also.

In those days there seemed an immense difference between the earth upon which men stood and the bright objects that shone down upon it from the heavens above. The earth seemed to be vast, dark, and motionless; the celestial lights seemed to be small, and moved and shone. The earth was then regarded as the fixed center of the universe, but the Copernican theory has since deprived it of this pride of place. Yet from another point of view, the new conception of its position involves a promotion, since the earth itself is now regarded as a heavenly body of the same order as some of those that shine down upon us. It is amongst them, and it too moves and shines—shines, as some of them do, by reflecting the light of the sun. Could we transport ourselves to a neighboring world, the earth would seem a star, not distinguishable in kind from the rest.

But as men realized this, they began to ask, “Since this world from a distant standpoint must appear as a star, would not a star, if we could get near enough to it, show itself also as a world? This world teems with life; above all, it is the home of human life. Men and women, gifted with feeling, intelligence, and character, look upward from its surface and watch the shining members of the heavenly host. Are none of these the home of beings gifted with like powers, who watch in their turn the movements of that shining point that is our world?”

This is the meaning of the controversy on the Plurality of Worlds which excited so much interest some sixty years ago, and has been with us more or less ever since. It is the desire to recognize the presence in the orbs around us of beings like ourselves, possessed of personality and intelligence, lodged in an organic body.

This is what is meant when we speak of a world being “inhabited.” It would not, for example, at all content us if we could ascertain that Jupiter was covered by a shoreless ocean, rich in every variety of fish, or that the hard rocks of the Moon were delicately veiled by lichens. Just as no richness of vegetation and no fullness and complexity of animal life would justify an explorer in describing some land that he had discovered as being “inhabited” if no men were there, so we cannot rightly speak of any other world as being “inhabited” if it is not the home of intelligent life. 

On the other hand, of necessity we are precluded from extending our inquiry to the case of disembodied intelligences, if such be conceived possible. All created existences must be conditioned, but if we have no knowledge of what those conditions may be, or means for attaining such knowledge, we cannot discuss them. Nothing can be affirmed, nothing denied, concerning the possibility of intelligences existing on the Moon or even in the Sun if we are unable to ascertain under what limitations those particular intelligences subsist.

The only beings, then, the presence of which would justify us in regarding another world as “inhabited” are such as would justify us in applying that term to a part of our own world. They must possess intelligence and consciousness on the one hand; on the other, they must likewise have corporeal form. True, the form might be imagined as different from that we possess, but, as with ourselves, the intelligent spirit must be lodged in and expressed by a living material body. Our inquiry is thus rendered a physical one; it is the necessities of the living body that must guide us in it; a world unsuited for living organisms is not, in the sense of this enquiry, a “habitable” world.

Which of the following best describes the primary purpose of the underlined final sentence of the passage?

Adapted from The Extermination of the American Bison by William T. Hornaday (1889)

With the American people, and through them all others, familiarity with the buffalo has bred contempt. The incredible numbers in which the animals of this species formerly existed made their slaughter an easy matter, so much so that the hunters and frontiersmen who accomplished their destruction have handed down to us a contemptuous opinion of the size, character, and general presence of our bison. And how could it be otherwise than that a man who could find it in his heart to murder a majestic bull bison for a hide worth only a dollar should form a one-dollar estimate of the grandest ruminant that ever trod the earth? Men who butcher African elephants for the sake of their ivory also entertain a similar estimate of their victims.

By a combination of unfortunate circumstances, the American bison is destined to go down to posterity shorn of the honor which is his due, and appreciated at only half his worth. The hunters who slew him were from the very beginning so absorbed in the scramble for spoils that they had no time to measure or weigh him, nor even to notice the majesty of his personal appearance on his native heath. In captivity, he fails to develop as finely as in his wild state, and with the loss of his liberty, he becomes a tame-looking animal. He gets fat and short-bodied, and the lack of vigorous and constant exercise prevents the development of bone and muscle which made the prairie animal what he was.

From observations made upon buffaloes that have been reared in captivity, I am firmly convinced that confinement and semi-domestication are destined to effect striking changes in the form of Bison americanus. While this is to be expected to a certain extent with most large species, the changes promise to be most conspicuous in the buffalo. The most striking change is in the body between the hips and the shoulders. As before remarked, it becomes astonishingly short and rotund, and through liberal feeding and total lack of exercise, the muscles of the shoulders and hindquarters, especially the latter, are but feebly developed.

Both the live buffaloes in the National Museum collection of living animals are developing the same shortness of body and lack of muscle, and when they attain their full growth will but poorly resemble the splendid proportions of the wild specimens in the Museum mounted group, each of which has been mounted from a most careful and elaborate series of post-mortem measurements. It may fairly be considered, however, that the specimens taken by the Smithsonian expedition were in every way more perfect representatives of the species than have been usually taken in times past, for the simple reason that on account of the muscle they had developed in the numerous chases they had survived, and the total absence of the fat which once formed such a prominent feature of the animal, they were of finer form, more active habit, and keener intelligence than buffaloes possessed when they were so numerous. Out of the millions that once composed the great northern herd, those represented the survival of the fittest, and their existence at that time was chiefly due to the keenness of their senses and their splendid muscular powers in speed and endurance.

Under such conditions it is only natural that animals of the highest class should be developed. On the other hand, captivity reverses all these conditions, while yielding an equally abundant food supply.

Which of the following best describes the role of the underlined passage at the end of the last paragraph within the passage as a whole?

Adapted from Are the Planets Inhabited? by E. Walter Maunder (1913)

The first thought that men had concerning the heavenly bodies was an obvious one: they were lights. There was a greater light to rule the day, a lesser light to rule the night, and there were the stars also.

In those days there seemed an immense difference between the earth upon which men stood and the bright objects that shone down upon it from the heavens above. The earth seemed to be vast, dark, and motionless; the celestial lights seemed to be small, and moved and shone. The earth was then regarded as the fixed center of the universe, but the Copernican theory has since deprived it of this pride of place. Yet from another point of view, the new conception of its position involves a promotion, since the earth itself is now regarded as a heavenly body of the same order as some of those that shine down upon us. It is amongst them, and it too moves and shines—shines, as some of them do, by reflecting the light of the sun. Could we transport ourselves to a neighboring world, the earth would seem a star, not distinguishable in kind from the rest.

But as men realized this, they began to ask, “Since this world from a distant standpoint must appear as a star, would not a star, if we could get near enough to it, show itself also as a world? This world teems with life; above all, it is the home of human life. Men and women, gifted with feeling, intelligence, and character, look upward from its surface and watch the shining members of the heavenly host. Are none of these the home of beings gifted with like powers, who watch in their turn the movements of that shining point that is our world?”

This is the meaning of the controversy on the Plurality of Worlds which excited so much interest some sixty years ago, and has been with us more or less ever since. It is the desire to recognize the presence in the orbs around us of beings like ourselves, possessed of personality and intelligence, lodged in an organic body.

This is what is meant when we speak of a world being “inhabited.” It would not, for example, at all content us if we could ascertain that Jupiter was covered by a shoreless ocean, rich in every variety of fish, or that the hard rocks of the Moon were delicately veiled by lichens. Just as no richness of vegetation and no fullness and complexity of animal life would justify an explorer in describing some land that he had discovered as being “inhabited” if no men were there, so we cannot rightly speak of any other world as being “inhabited” if it is not the home of intelligent life. 

On the other hand, of necessity we are precluded from extending our inquiry to the case of disembodied intelligences, if such be conceived possible. All created existences must be conditioned, but if we have no knowledge of what those conditions may be, or means for attaining such knowledge, we cannot discuss them. Nothing can be affirmed, nothing denied, concerning the possibility of intelligences existing on the Moon or even in the Sun if we are unable to ascertain under what limitations those particular intelligences subsist.

The only beings, then, the presence of which would justify us in regarding another world as “inhabited” are such as would justify us in applying that term to a part of our own world. They must possess intelligence and consciousness on the one hand; on the other, they must likewise have corporeal form. True, the form might be imagined as different from that we possess, but, as with ourselves, the intelligent spirit must be lodged in and expressed by a living material body. Our inquiry is thus rendered a physical one; it is the necessities of the living body that must guide us in it; a world unsuited for living organisms is not, in the sense of this enquiry, a “habitable” world.

What is the primary purpose of the fourth paragraph?