The Origin of Species-Chapter Summaries

 

Chapter 1-Variation Under Domestication

 

Darwin opens up the subject of variation by elaborating about how the general features of closely related subspecies can differ in large extents. It is of common belief that when groups of the same species are exposed to different conditions, then over the course of generations, a variability between the different groups will emerge. That emergence of variability is continuous as well, and a greater degree of separation becomes visible over time. Once this basis is established, he begins to elaborate upon multiple theories of why this phenomenon exists. Darwin attributes the occurrence to the capabilities of the reproductive system; various traits emerge in an individual due to inheritance. The instances in which various forms of life breed plays an interesting role as well. Domesticated animals are generally “weaker” than their wild relatives yet breed quite well under confinement, while their relatives taken from nature lack this ability.

 

Once the basics are established, Darwin uses pigeons to illustrate the effects of domestication. He notes that among the domesticated individuals, less variability (difference among common traits) is observed than with the closely related species in nature. Darwin puts forth a novel theory that originated amongst a group of naturalists in which all domesticated varieties of pigeon descend from the rock-pigeon. Although many species of domesticated pigeon seemingly have no relation to the bluish-colored rock-pigeon (white fantails and black barbs most notably), when Darwin performed a cross-breeding experiment between the two marked species, and bred the second generation, the third generation was blue and color with virtually the same traits as the rock-pigeon. Further evidence for this point of view is that when the various groups of pigeons are observed across a range of lands, the characteristics of the birds progress in a smooth and sequential manner.

 

The last major topic of the chapter is the principle of selection. Darwin states that even the most “primitive savages” select and breed only certain members of their stock. In this way the quality of their herd gets better over time. Darwin attributes this power as the cause of variability. Over time as changes continually emerge, so does the theme of variation.

 

Chapter 2-Variation Under Nature

 

In the second chapter, Darwin takes a more elaborate look into variation and covers the ambiguous differences in separating species from variety. He begins by stating that species are determined by distinct acts of creation among most naturalists, and that varieties are differences amongst a species. There is a grand debate, however, over which individuals to call species, and which varieties. Darwin uses two plants which are seemingly unrelated in each and every characteristic trait, yet he only calls them varieties due evidence that they in fact descended from the same parent plant. There are ultimately no specific criteria or line of demarcation separating species from sub-species. Darwin uses young naturalists as pawns to prove his point in this situation. He points out that whenever an up and coming naturalist is unsure how to classify a group (species or variety), then he looks in the history books for analogies. The reasoning the student uses is that if it was done a certain way in the past, it must be the correct way; however, Darwin does not see this as the case.

 

Darwin then diverges into the general differences between larger and smaller genera. The pattern is for larger genera to have more variation amongst the species and for the opposite to be true of smaller genera. When this trend is viewed from the standpoint in which species are highly marked varieties, he finds the so called species of the larger genera to be more “varieties” than the species of the smaller genera. He refers to varieties as incipient species and shows how variation progresses in a continuous form starting at parent species then moving to incipient species and ending at individual. His argument closes by reiterating the ambiguity between species and variety.

 

Chapter 3-Struggle For Existence

Darwin builds upon the tenets mention in chapter 1 of artificial (human controlled) selection and delves into the ability of nature to literally pick out specific traits and propagate them. The power of man to perform selection is incomparable to that of nature which has diversified the world. This all relates to the struggle for existence. Animals are in a constant struggle to obtain food, avoid prey, bear the elements, and reproduce. Even with all these difficulties, the factor which possesses more weight than all the others is competition amongst others in the species or sub-species.

 

Reproduction is set to create the most product, and if individuals did not have to struggle and compete amongst one another for the world’s limited resources, then populations would grow exponentially to infinity without bound. In the struggle for survival, some will be victorious, while others will fail. In this way, nature selects the most fit to live and reproduce; it is by this method that variation emerges.

 

Darwin then delves into the relationships between various unrelated animals and how they are all dependent on one another. He goes to say that the mouse population is dependent on cats, and that triggers a boom in the bee population (because mice destroy bees nests), then the large bee population has the ability to pollinate the local flowers-just one of the countless ways in which all life is interdependent (who would have thought that cat population in an area could determine flower population).

 

Chapter 4-Natural Selection

 

Darwin reintroduces the topic of natural selection from the previous chapter. The topic of variation is brought up as well as possible explanations for the phenomenon. It has been greatly assumed that variation amongst related life forms is a direct effect of the environment, when it is in reality the direct effect of the struggle to survive.

 

Now that nature’s powers of literally hand-picking certain traits has been established, Darwin compares natures abilities to those of man when it comes to selection. Man can only act upon the superficial characteristics of an organism in relatively desperate acts to improve the quality of his stock. Nature, however, acts upon every component of its target at a slower rate than compared to artificial selection, yet leaving a bigger bite at the end.

 

Survival is not the only goal for the individuals of a species; without proliferation, the species will die out in a single generation so reproduction is perhaps the most important order of business for a living creature. In the related phenomenon called sexual selection, males of a species compete with each other for the chance to reproduce. Many varieties of birds are known to put on magnificent displays in order to entice a lone female. Whichever male is seen as the most suitable partner will get to pass on his traits while the others will not; out of this persistent action year to year, these secondary sexual characteristics will further evolve in as generation upon generation takes part in the same rituals.

 

After Darwin described the processes of selection, he began to focus on the conditions which determine the efficiency of this natural phenomenon. Some are lead to believe that complete isolation (such as that of a desert island) would be optimal for the formation of novel varieties since there is no interference from an outside source. This is a fallacy because although desert islands do provide isolation, they do not provide much potential variety because their population numbers are low. It is in fact continent which provide the grounds for the formation of new varieties; Australia is the quintessential proof for this statement, because on this relatively new continent, the process of full-blown natural selection and evolution may be observed.

 

Darwin then enters into several examples of natural selection and describes how continual divergence of character leads to new varieties. The principle states that a species will naturally seek anywhere from one to several routes at any given point in its history to try and solve the problem of survival. Novelties and monstrosities will become further modified and as the sub-species begin to form, they basically kill off the less advanced parent species. In this manner, Darwin then puts his principles to the test as he illustrates a comprehensive example of how about ten species of a single genus can transform into fifteen species of five different genera.

 

Chapter 5-Laws Of Variation

 

The first major topic of this chapter is the effect of use versus disuse. It is clear that animals have their own strengths and weaknesses, such as the ostrich, which can run and kick very well yet cannot fly. Natural selection has clearly acted upon a progenitor to the common ostrich (a progenitor which probably had moderate running/kicking as well as flying capabilities). It apparently came as a greater advantage for the ostrich to have more leg power, so over countless generations, the ostrich was perfected into a powerful runner and relentless kicker. The flying capabilities of the ostrich then began to dwindle due to lack of necessity (there is no need to be superfluous when picking capabilities). The wings of the ostrich began to atrophy and become futile in comparison to their previous potential. Patterns such as these can be applied to countless members of the animal kingdom.

 

Darwin then covers the topic of acclimatization, or a habitual response to environmental behaviors. He shows how certain plants and animals are adapted to the temperate climates such as the conventional oak while certain others are adapted to a more extreme conditions (such as the succulents in the harshness of a desert). Of course rearranging such mentioned plants into converse biomes would only lead to death, yet that does not mean there is absolutely no versatility.

 

The short section on the effects of climate leads to the laws of correlation of growth, which build upon the principles of use, disuse, and habit. It is often observed that the presence of certain traits signal the presence of others (e.g. cats that have blue eyes and are death). Though this phenomenon is frequently attributed to homology in body parts, use and disuse have their importance as well. The presence of one trait (large antennae) could lead to a consequential loss of another trait (eye sight). The laws governing such variability are extremely numerous and obscure, yet possess a great deal of interest to the curious observer.

 

The last major point of the chapter is that if a specific character of one species is enhanced to a high level, will differ to a high degree to the corresponding part in a more closely related species. When a divergence occurs in specific organs or characters, then as time elapses, the space between which the original organism has diverged (in relation to the specific character) will be immense. This is extremely frequent amongst secondary sexual characters (not directly involved in reproduction) as the males become greatly enhanced over relatively short periods of time as they try to catch the eye of a lone female.

 

Darwin closes the chapter by touching on the occurrence of reversions amongst different species of the same genera to the aboriginal form. This provides further evidence to Darwin’s theory of enhancement over time.

 

Chapter 6-Difficulties On Theory

 

In any work of hypothetical scientific reasoning, it is inevitable that opposition and counter-examples will appear, which could potentially disprove the theory. In this chapter, Darwin acknowledges his opposition and meets them with reasoning which further supports his theory. The first category of opposition which Darwin addresses is the fact that transitional varieties among species of a genus are rarely observed. According to the theory, a less specialized variety diverges continually into a more “advanced” group of individuals, and this change does not occur in leaps, but in nearly undetectable baby steps as generation gives rise to generation. The absence of such transitional varieties sparks much skepticism, as there is also rarely any fossilized evidence of a once existent intermediate group of individuals. Darwin illustrates how an absence of such intermediates is to be expected, because as divergence and specialization progresses, the new varieties ironically eliminate their less capable predecessors and hence there lacks a living variety which gave rise to the present group of individuals. The lack of fossilized evidence of such intermediates is to be expected as well since the necessary conditions of fossilization are difficult to encounter and many of such organisms are lost in history.

 

The second large group of criticisms which Darwin addresses include possible limits to his hypothesis. It appears ludicrous that creatures which are strictly adapted to aquatic habitats could transform into land animals, or a squirrel become capable to glide through the air. Darwin uses several examples to show how magnificent transformation sometimes to occur. Natural selection happened to favor a squirrel with slight amounts of membranous tissue connecting its limbs, and over the course of generations, a squirrel with the ability to glide towards its prey, or prevent against a potential fall emerged. Geese are examples of creatures which once inhabited aquatic habitats (webbed feet) and then adapted themselves to the dry land, still with a few inherited reminders of their wet past.

 

Even the creation of organs as complex and magnificent as the eye can be explained by natural selection. An early form of the eye was perhaps nothing more than an optic nerve coated by pigment. Natural selection favored those with better vision, hence slightly better mechanisms of sight, and through the process of baby steps, the eye as it is known today was formed. As for the existence of organs which seem to have only trifling importance, their existence may be explained by their potential use by the lineal ancestors of the variety, acting as souvenir. Natural selection really is a potent force, and is responsible for the countless variations that may be observed in the world today.

 

Chapter 7-Instinct

 

Another topic of skepticism centered on Darwin’s theory is the presence of instinct. Darwin starts by making clear the fact that instinct is inherited, as when baby animals, clearly with no experience, make their first nest, sound their first cries, or seek their first meal. Similarly to the previous points of skepticism, instinct can be treated just like a physical feature in that it can be acted upon by the principle of natural selection.

 

A superficial overview of the topic would lead one to believe that variation of instinct is impossible and simply nonexistent; however, such variation of gradation may by found through several examples, including behavioral patterns of birds in the species in the northern versus southern regions of the North American continent. One example which requires attention is the slave-making ability of certain insects. A specific genus of insects in the European continent is well known to rely on other insects for all their daily needs (analogous to a king and his slaves). There is a great deal of variation, however, to the degree in which the different varieties are capable of enslaving their servants; one species in Europe uses its slaves to only a minimal extent, while the same species in Switzerland, utilizes its slaves for countless daily tasks. The requisite gradation of Darwin’s theory immediately becomes visible.

 

The nest making ability of bees also comes in a package of varieties. The humble bee uses a simple cocoon-like structure to store its honey, continuously adding more of such compartments as its honey supply increases. The Mexican genus of Melipona is known to make spherical cellular structures into which honey may be placed. Then the conventional hive bee is said to construct a perfect honey storing unit, with hexagonal cells surrounded by a layer of wax one-fourhundredth of an inch thick. The hive bee economizes its wax to the fullest potential, and not even natural selection can create a further improved structure. This example only proves that instinct, although intangible, can still be worked on by natural selection, perhaps to a more wondrous extent than the physical nature of species.

 

Chapter 8-Hybridism

 

The last major area of skepticism centered on the theory of descent with modification is a strange series of phenomena that occur involving the fertility of hybrids. It has been often noted that when different species are crossed, their offspring are sterile while the progeny of mere varieties often become highly fertile. This such result leads the ordinary observer to believe that there is in essence a difference between species and varieties, refuting the tenets built upon in chapter two and ultimately destroying Darwin’s entire theory.

 

Plants provide perhaps the best test individuals for such studies, and several biologists have devoted their entire careers to these occurrences. As supported by much of the evidence obtained by experimentation, the root of the phenomenon clearly lies within the reproductive system. The overall systematic affinity (resemblance) of two individuals has been proven to posses no effect in terms of sterility of the first cross and the hybrid. Certain plants which are considered to be varieties by the most eminent naturalists actually give way to hybrid progeny which are almost completely sterile. The opposite has been proven to be true in crosses between two distinct species. Such observations show that the previously mentioned “rule” contains no universality and that they are caused by unknown differences involving the reproductive systems of various forms of life. The idea that there is ultimately no difference between species and variety still contains reasonability.

 

Chapter 9-On The Imperfection Of The Geological Record

 

As a continuation of the section which elaborates upon the lack of intermediate forms between existent species, Darwin covers the geological aspect of why there is not even fossil evidence of many such transitional varieties. Darwin’s theory states that certain traits amongst a parental form of individuals are naturally selected and propagated through the struggle for existence, and through this method, over time, new species begin to emerge. The fact that Darwin’s theory is a gradual process shows that links between current species must either now exist, or have existed in the past. Darwin then enters into the specialized conditions required for fossilization and why such links are completely unknown.

 

The first major issue is that fossilization takes a long time, and maybe what Darwin is saying simply did not have sufficient time to take place and each species was created individually. The response to this point is that geologist have shown that the world is much more than 10,000 years old and that the mineral deposits that have been surveyed would take upwards of billions of years to form. With the time issue resolved, Darwin shows how fossilization occurs during periods of subsidization, and that there are often long intervals in which there is no fossilized evidence being accumulated of the existent species. According to the theory, natural selection favors specific varieties over the parent form, so extinction ensues. Such intermediates which are not fossilized will then become lost in time, so it the lack of transitional links is to be expected.

 

A last point is the abrupt appearance of certain groups or forms in the fossilized areas. Many of the oldest layers in a fossilized rock formation will lack a certain group of individuals, which seem to suddenly appear at the newer levels. Such occurrences can easily be explained by the immigration of various groups from one homestead to another. Recent developments which show that over long periods of time the Earth’s tectonic plates rearrange themselves in varying formation and certain continents were located on what were now oceans, etc. The dynamic nature of the Earth must be taken into account when considering such fossilized records of life.

 

Chapter 10-On The Geological Succession Of Organic Beings

 

As the second of a series of chapters concerning the geological aspects of descent with modification, it starts by reemphasizing how new species arise through only slow processes. Over the years as certain forms are built upon and evolved, parental and other closely allied forms become rarer and eventually become extinct. The rate at which these actions occur, however, is not constant and various under the circumstances. Once a species and its progenitor become extinct, there is no chance of an exact recurrence because the direct chain of life has been broken and any “replacement” that results from the selection of another group of individuals will still contain the initial differences. Life is like a tree; many branches emerge out of a single stem, and when one branch falls off, it will never be replaced.

 

After another large section dedicated to the issue of extinction, Darwin talks about how life changes simultaneously throughout the world. The existent fossil records of any region of the world all illustrate the dynamics in terms of species. European Chalk formations can hence be detected in the Americas and India, where not a fragment of mineral chalk can be found. An almost parallel sort of succession occurs throughout the world and the Earth’s creatures all evolve in the same manner.

 

last major topic of the chapter covers the various affinities living species have with their ancient progenitors and intermediate links. Descent with modification acts in varying degrees, as mentioned earlier, so the “difference” between allied species and their ancestors will be of varying degrees as well. “Maps” can be created which illustrate evolutionary paths over several generation and the amount of overall difference between the species which emerge. A last point which Darwin makes is that evolution would not profoundly affect the embryos of a species, but the fully developed product; and that if this were true, we could conclude that embryos are homologous in all structures. Recent studies focused on embryos has shown such homology in structure.

 

Chapter 11-Geographical Distribution

 

Now that Darwin’s theory appears feasible to the readers, Darwin looks into why certain species are distributed as they are, and how this may be accounted by descent with modification as well as natural processes which affect the world’s geography. Certain species are known to inhabit all corners of the discontinuous world; hence, the average observer, knowing that each species has a common ancestor, would be puzzled. With barriers scattered virtually everywhere throughout the world, one would think that migration throughout the world is ultimately impossible. Darwin seeks to prove his critics wrong by providing ample proof that there are ways for certain forms of life to cross barriers such as an ocean, and that today’s geographical distributions may be explained in a scientific manner.

 

Plants have been by far the most frequently studied test forms when it comes to dispersal over a long range of salt water. Darwin has set up test in which he submerges plant seeds in artificial salt water for periods up to a whole month. Based on the germination percentages after the submersion in the salt water, he determined that 10% of all plant seeds have the ability to travel a 900 mile space of sea (calculated according to oceanic currents and a month’s span of time). These tests were done with random species of flora and although rough, the results prove a point that seeds are capable of being dispersed over several hundred miles of ocean. Other means of seed dispersal include drift timber, icebergs (during the Ice Age), birds (which eat seed and are known to excrete many whole in their droppings), and fish. When all of these factors are combined in action for countless thousands of years, it is inevitable that there will be a great dispersion of the world’s flora.

 

It has often been noted that many of the same species of fauna exist on the mountain ranges of separated continents, yet are absent throughout the ranges between such areas. To find the answer to such a strange occurrence, one must turn to the last Ice Age. As the Earth began to cool, creatures far north and south that inhabited the temperate region were forced to migrate towards the tropics for understandable reasons. This migration would relocate many animal groups, but as the Earth began to warm once again, those that migrated to escape the freezing cold would either have to turn back to their old homes, or seek a mountain range that provides cooler temperatures. Those that continued to life in the intermediate ranges would eventually die off due to the hotter climate. Such a scenario provides a viable explanation as to why such odd distributions are observed across the world’s mountain ranges present day.

 

Chapter 12-Geographical Distribution (continued)

 

Darwin continues his section on the distribution of species by further explaining several other examples of why such geographical anomalies occur under the principles of descent with modification from a common ancestor. The phenomenon of distribution of fresh water productions throughout continents which are separated by salty ocean water provides an excellent opportunity for Darwin to show how relocation mechanisms have such a wide spectrum. With regard to fish, it is easy to visualize how their ova may be transported between neighboring lakes and rivers through flooding. It is not even extremely hard for fresh water fish to adapt themselves to a saltier environment, allowing them to travel the shores of a sea. Darwin also gives accounts of ducks traveling from pond to pond covered in duck weed which contains the ova of many fresh water shells. He also mentioned a time when a water beetle flew onto the Beagle 45 miles off shore, and similar beetles have been known to have such shelled creatures adhere onto their exoskeleton.

 

This eventually leads to dispersal throughout oceanic islands, a topic familiar to Darwin from his earlier voyage across the world. Islands host an isolated and favorable environment for natural selection to occur along with its counterpart, speciation. The means of relocation mentioned earlier allow an ample supply of individuals for natural selection to operate. Although such young volcanic islands have relatively few species, the ones present throughout the various islands are often unique to a single island (or a chain of islands). Many creatures such as frogs are not found on such islands since they are unable to be transported over the sea water. An interesting point which Darwin brings up in why some species are only unique to one island of the Galapagos instead of the entire chain is that the islands are different (different individuals, etc.) and natural selection would simply not allow inter-island dispersal of many such species. The last major dogma sparked by such island phenomena is that the inhabitants of an island chain are most closely related to those species of the nearest continent or the source from which the island populations arose. This makes sense because it is obvious that offspring will always share similarities to their recent ancestors.

 

Chapter 13-Mutual Affinities Of Organic Beings: Morphology: Embryology: Rudimentary Organs

 

The last main goal of Darwin’s revolutionary work is to provide an overview by which life is related, and how these relations may be used in classification. Naturalists have classified organisms on a group subordinate to group basis in order to map what was once thought the plan of creation. This early taxonomic system actually proves beneficial to the theory that life has common progenitor(s), and the paths of modification are clearly shown through this comprehensive categorizing. Darwin shows how the most vital organs often vary the most amongst species while the trifling characters remain uniform; such a phenomenon is clearly explainable by natural selection in that the most important structures on a living creature are most apt to modification by selection, while the other parts remain conserved. This knowledge must be taken into account when grouping individuals, one must look at the subjects from all aspects to categorize them appropriately.

 

This overview of the similarities between various groups leads to the phenomenon in which the embryos of distantly related species contain nearly identical features. Darwin explains this occurrence by noting how natural selection acts upon characters that usually take effect upon maturity, and the embryo remains unaltered. Certain features on the embryos of land based animals highly resemble such characteristics of aquatic groups, inferring that there was a common ancestor that lived in the water and subsequently diverged. Recent microbiological experiments have shown such similarities in the early embryos of humans, chickens, and certain fish.

 

There are even homologous structures between fully developed humans and whales, such as the presence of five “digits” and just an overall similar skeletal system. Sometimes natural selection acts upon a single structure located on the common ancestor, creating different features on the multiple species that result. Aside from fully developed organs, the rudimentary parts of unrelated groups provides even more compelling evidence that all of life descended from a common progenitor. Snakes are well known to contain the rudiments of a pelvis and hind limbs, and although such parts are of no purpose to their possessor, they provide insight on the evolutionary history of snakes. Countless examples of similar observations may be given, which further support Darwin’s theory.

 

Chapter 14-Recapitulation and Conclusion

 

In the last chapter, Darwin begins by restating the many objections and difficulties that have arisen concerning his theory. It seems nearly impossible that organs such as the human eye, so highly perfected, could be the product of anything but independent creation. Darwin reiterates this point from a previous section to show to the reader that natural selection works taking only baby steps, yet for an inconceivably long period of time. Darwin quickly turns to the non-universal laws governing the sterility, that is characteristic of hybrids, showing that there is ultimately no fine line between species and variety, which is a significant prerequisite to the theory of descent with modification; however, the lack of intermediate forms between the early ancestor and the current species alone could prove that Darwin’s theory has no basis. Darwin counters such criticisms by referring to the dynamic nature of the conditions on Earth, and the difficulties associated with geological fossilizations. Darwin then goes on to restate the important points of his theory: unlimited resources create a struggle for survival, in which the fittest go on to reproduce and pass down their desirable traits to the progeny, which gradually creates newer forms and species. Darwin closes by stating that the theory of evolution may apply to the extent that all life has a single common ancestor, and that countless periods of modification have led to the biological diversity which is observed today.