LSAT Reading : Main Idea of Science Passages

Study concepts, example questions & explanations for LSAT Reading

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Example Questions

Example Question #67 : Science

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 most accurately describes the main idea of the passage?

Possible Answers:

The presence of non-intelligent life, like lichens or oysters, is not sufficient to make another world inhabited.

In order for a world to be considered inhabited, it must have intelligent life with material bodies.

The inhabitants of other worlds could have very different bodies than those of humans.

Advances in science have allowed us to contemplate whether other worlds are inhabited.

As science has progressed, people have wondered if there are other worlds that might be inhabited by creatures like ourselves.

Correct answer:

As science has progressed, people have wondered if there are other worlds that might be inhabited by creatures like ourselves.


The credited response is the only one that addresses the thesis of the passage as a whole, rather than the points of individual paragraphs or sections. While the other responses are supported by the passage, they do not capture the overall aim of the passage as a whole, which is what this particular type of question asks about. There are several parts and subsidiary ideas in this passage to look for in determining the credited response: the advancement of science, the conditions needed for a world to be considered inhabited, and how like human beings the inhabitants of other worlds must be. All of these are present in the correct response.

Example Question #68 : Science

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 best summarizes the author's main idea in the passage?

Possible Answers:

Artificial selection allows humans to create certain specific differences between different living things over time.

All kittens have different qualities than their littermates, no matter how superficially similar they seem at first.

Artificial selection is one of many causes of differences in living things.

There are a wide range of different characteristics present in a species of organism.

Carefully selecting different desirable characteristics helps improve the general health of all living things.

Correct answer:

Artificial selection allows humans to create certain specific differences between different living things over time.


The author has two very different paragraphs in this passage, which detail two very different things, inherent differences and artificial selection; however, the first sentence of the second paragraph shows how they are linked, as it notes that the great diversity on earth is caused through artificial selection.

Example Question #69 : Science

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 best summarizes the author's main idea?

Possible Answers:

The nature of a living organism is too difficult to understand, and attempting to define a living organism is not worthwhile.

The best way to understanding complex ideas is through a variety of metaphors.

The constantly changing nature of a living organism means that the definition of a living organism is constantly changing.

The full conception of what constitutes a living organism requires understanding on a number of different levels.

A living organism is actually quite simple to understand if one takes time to study it.

Correct answer:

The full conception of what constitutes a living organism requires understanding on a number of different levels.


The author's simple goal is to outline precisely what a living organism is; however, in order to do this, the author shows how difficult it is to make such a precise definition for something as singular and complex as a living organism. The author's main idea is that the conception of a living organism is best understood through a variety of methods.

Example Question #71 : Science

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 best summarizes the author's main idea in the passage?

Possible Answers:

Immutable characteristics are the chief element which unite all species.

Each species has immutable characteristics that distinguish it from other species.

The idea that every essential organ is immutable is not scientifically accurate.

Every individual of every species has important variations that are unique.

Individual differences among members of a species are usually inconsequential.

Correct answer:

Every individual of every species has important variations that are unique.


The author's main theme in this passage is the nature of differences between individuals among a particular species. For the author, the most important aspect of the variability between individuals is just how many there are, as well as the sheer number of variabilities being the most consistent feature of species. In this way, the author argues that variability is, in fact, the most consistent presence in the studies and experiences of a naturalist. An "immutable characteristic" is an aspect of something that is unchanged or unchanging over time. Given the emphasis the author places on diversity and variablity, it seems unlikely that the main idea would be concerned with the unchanging nature of anything (especially anything in under the purview of "naturalist" study).

Example Question #72 : Science

"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 best summarizes the author's main idea in the passage?

Possible Answers:

Neanderthals were a significant presence in Europe for a period before modern humans arrived in Europe.

Human evolution was not as straightforward as is commonly thought, but instead comes from a blending of human ancestors.

The science is unclear regarding what happened to the Neanderthals to make them become extinct.

Neanderthals and modern humans greatly differed from each other in many significant ways.

Neanderthals were superior to humans in Europe for a range of about 5,000 years.

Correct answer:

Human evolution was not as straightforward as is commonly thought, but instead comes from a blending of human ancestors.


While the passage mostly discusses Neanderthals, the point of discussing them is to describe the nature of human evolution. Notably, the author highlights how the belief that human evolution was neat and orderly is wrong, showing the coexistence of Neanderthals with modern humans, and their possible genetic mixing, as a way of demonstrating how complicated human evolution really was.

Example Question #1 : Main Idea Of Science Passages

"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 best summarizes the main idea of the passage?

Possible Answers:

Alfred Russell Wallace attempted to take the credit for a theory which was actually Charles Darwin's.

Alfred Russell Wallace played an important and little known role in the development of Charles Darwin's theory of evolution.

Charles Darwin and Alfred Russell Wallace worked closely together to develop the theory of evolution.

The credit that Charles Darwin has received for the theory of evolution should rightly go to Alfred Russell Wallace.

Correct answer:

Alfred Russell Wallace played an important and little known role in the development of Charles Darwin's theory of evolution.


The passage details the work of Alfred Russell Wallace in developing a theory of natural selection, but the author largely focuses on the way in which Wallace's work overlapped and interacted with the research done by Charles Darwin. This makes the main idea of the passage that Wallace played an important role in the development of Charles Darwin's theory.

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