On the Origin of Species by Charles Darwin
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#6 I am yet to finish those of January :)
Apparently, Darwin was going to publish a huge tome that would take several more years to finish. It was never finished and the first two chapters were published as The Variation of Animals and Plants under Domestication, and the rest was published posthumously as Charles Darwin's Natural Selection, Being the Second Part of His Big Species Book Written from 1856 to 1858 (editor R. C. Stauffer). When Wallace sent him an essay proposing the same theory as Darwin had been laboriously pouring fourth, Darwin asked Wallace to present their ideas together at a scientific meeting so that they would both get the credit due. Then, Darwin quickly wrote what he considered an abstract to his "big book." This abstract is what we're reading. Apparently, there were 5 or 6 editions during Darwin's lifetime, and Darwin changed the way he phrased things for each edition--trying to defend criticisms and make things clearer. I am uncertain which edition I'm reading and whether all modern editions come from the same one of those original 6.
I was hoping that my introduction would have a little more about how evolutionary theory evolved since Darwin's time--as I know that Darwin's theory is amazing for its time but does not explain everything. I know Punctuated Equilibrium is Stephen Jay Gould's update to Darwin's theory, but I don't know what the other current theories are.
Since no one has posted for a while, I don't have to feel left behind. :)
I've been dealing with RL pressures by setting aside books that demand mental effort. :-)
I know that Darwin's theory is amazing for its time but does not explain everything.
He didn't know about genetics, for one thing.
I don't know what the other current theories are.
The conflicts and controversies among evolutionary biologists are extremely important to them, and are exploited by creationists, but pale in comparison to the core idea of descent with modification. I don't know whether Darwin got anything outright wrong. He raised lots of questions.
There's an article in March 5 New Yorker about a current controversy re altruism and kin selection.
I'm reading a Project Gutenberg edition (though I have a print edition too), says it's 1st edition. I vaguely recall that he toned down human evolution in later editions.
I am not very familiar with evolutionary theory, but my understanding is that the way Darwin explained evolution couldn’t really have worked based on the fossil records. Apparently, there are some huge leaps in the evolutionary tree that couldn’t be explained by the slow-and-steady progress of pure natural selection. Stephen Jay Gould presented his theory of punctuated equilibrium to build on Darwin’s ideas, while explaining these jumps. I know there are other theorists out there, but Gould is the most famous and the only one that I know anything about. My question was meant to ask if anyone else knows of other theories/theorists that explain these inconsistencies (other than creationism, fine tuning, and other such arguments)
Nor do I say that Darwin was wrong. Actually, based on his introduction, he only suggests that natural selection is ONE of the methods that characteristics of species are chosen. Which makes him right even given the newer evidence in fossil records. :)
Not sure what you mean by "extreme evolutionary theorists"? There are some evolutionary theorists who step beyond the limits of science into theology (or lack thereof), which is fully their right as humans, but not within the scope of science.
Darwin didn't have much fossil record to go on. So I gather his concept of steady gradual change was questioned as the fossil record was (and is still being) filled in.
I've scouted around a bit since my last post. Darwin got the mechanism of acquiring/changing features wrong, which is unsurprising. I guess I'll see as I read; obviously he didn't know, but I gather he speculated erroneously. And because he was focused on competition, he considered altruism a problem.
Evo-devo is indeed way cool. A book that got good press a few years ago was Endless Forms Most Beautiful by Sean B. Carroll.
Not sure what you mean by "extreme evolutionary theorists"?
Actually, all I meant by this is people (like Stephen Jay Gould and Richard Dawkins) who write essays about how there's no point in even talking to the creationists because they're so stupid. I think it's rather arrogant to feel this way, though I understand that it must be annoying to be constantly attacked by ideas they feel are ridiculous. I think it would be better to just ignore them, although that would encourage just as many attacks as replying to them does. :) It just bugs me when theorists think opposing theories are “stupid” rather than simply “misinformed” or “unlikely.” But that’s just me (shrug).
Darwin didn't have much fossil record to go on. So I gather his concept of steady gradual change was questioned as the fossil record was (and is still being) filled in.
He didn’t have a fossil record or genetics—that’s what makes his book so amazing! I think this is a topic that will never fully come to rest since it is really impossible ever to know what happened over such a long period of time. It is impossible to design experiments, so all we can do is conjecture and theorize. But I think we’re coming up with very reasonable theories.
And because he was focused on competition, he considered altruism a problem.
I’ve followed the altruism debate for a while. My feeling is simply that altruism helps protect people in your social group (who are probably related to you genetically at some level), thus increasing the number of people in your social group who are capable of protecting you AND increasing the number of people who carry similar genes to yourself. The problem with Darwin’s theory (I think) is that he focused too much on individual competition and didn’t consider that people within one’s social group would likely carry some of one's own genes. Of course, he didn’t know what genes were. :)
Also, I’ve always found stories about animals that “adopt” babies of a different species. Dogs that nurse motherless kittens, cats that nurse motherless squirrels, etc. I have no doubt that these animals know that the foreign babies aren’t their own…they probably even sense that the foreign animals aren’t of their own species. So why do they do it? Clearly, altruism isn’t just a human trait and therefore not necessarily a function of higher-intelligence morality.
There is no way to test creationism scientifically because it is fundamentally an idea based on faith and is therefore not experimentally testable.
Because of this insurmountable time-frame, the theory of evolution is a softer science than, say, the experimental testing of drugs.
who write essays about how there's no point in even talking to the creationists because they're so stupid
I don't care for the tone either, but in defense of biologists, although they personally could just continue to go about their business, science education is under chronic attack, and biologists are under pressure to step out of the ivory tower and get involved. And there is a difference between opposing scientific theories, and opposing cultural ideas that do not merit the label of "theory". After years, decades, a century, of refuting the same arguments over and over and over (http://www.talkorigins.org/indexcc/list.html), and meeting deliberate distortion, people understandably get weary.
Unfortunately, the antagonistic attitude can spill beyond what I'd consider acceptable boundaries, and get directed at people with any sort of religious belief or practice, or people who are simply honestly ignorant.
My feeling is simply that altruism helps protect people in your social group
Yeah, seems a balance between competition and cooperation is necessary.
Clearly, altruism isn’t just a human trait and therefore not necessarily a function of higher-intelligence morality.
I think few, if any, traits are exclusively human. :-) We are a thin veneer over everything that came before us and is built into us.
One time, I was listening to an NPR show interviewing Richard Dawkins. Somebody called in and made the point (yes perhaps arrogantly...) that life defied the second law of thermodynamics: entropy (disorder) always increases in a closed system. The guy's point was that life is organized...therefore entropy is not decreasing.
There's an easy answer to this. The man didn't understand that the second law of thermodynamics only applies to a CLOSED system--that is, a system which does not interact with its environment. I (a living being) eat, breathe, excrete wastes, etc. Therefore I am an OPEN system that interacts with its environment. The second law of thermodynamics doesn't apply.
Instead of making this explanation (which I'm sure Dawkins must have a firm grasp on) he disregarded the caller in such a way that didn't answer his question and made it seem stupid. It wasn't stupid, it was ignorant.
So I think these guys need to make a LITTLE more effort to get out of their ivory towers! ;)
Yeah, from your description I'd agree, not handled well. There is an equally arrogant attitude among creationists of "2nd law of thermodynamics, so there! nyah!", and it does get to be tiresome, but the former Professor for the Public Understanding of Science should recognize that on a radio program he is speaking to a large audience, and even people who are receptive to the idea of evolution are not necessarily familiar with the evidence.
Darwin makes three major points in this chapter:
1. He starts by suggesting that the most important factor in determining traits of animals is inheritability. He notes that, within a single species, our cultivated plants and animals are much more variable than those found in nature. There is some argument about whether characteristics of offspring come from the development stage or the pre-conception stage--but Darwin believes it is pre-conception stage. One bit of evidence for inherited traits is that vary rare variations in the parent can pop up regularly in the offspring. Because the trait was rare to begin with, and common only to that individual's offspring afterwards, it is unlikely to be due to environmental factors during development. He almost entirely ignores the Lamarckian concept of environmentally-induced development AFTER birth, but admits that embryological development plays a role; though its role is less important than that of inherited traits.
2. He discusses variations within breeds of domesticated animals (and plants). He believes that despite the huge variation of pigeon breeds, they all arose from one ancestral species (the rock pigeon). His evidence for this claim is two-fold: A) If different breeds are mated, then after a few generations the offspring look very much like the wild rock pigeon; B) If all pigeon breeds came from a different species, then there would be around 7-8 different species of wild pigeon. But there is only one species of wild pigeon similar enough to be related. Since all breeds of pigeon have exactly the same survival instinct, it is unlikely that so many different ancestral species would disappear.
Despite this very rational argument that all pigeons are from the same ancestral species, he believes that different breeds of dogs were domesticated from different ancestral species. His explanation is basically "from the existing evidence about dogs" and isn't very clear. He makes a comment about there being several different types of fox--which contrasts his evidence that there is only one type of wild pigeon. I'm not sure where he was going with this dog thing...but I guess dogs CAN be a bit confusing since coyotes, dogs, and wolves can interbreed and produce fertile offspring, whereas usually animals are defined as being of a different species specifically when they can NOT interbreed and produce fertile offspring (like horses and donkeys or lions and tigers).
3. He then points out how humans have selected the traits of different breeds. This is frames the scene for his personal theory of natural selection. He notes that there are two ways humans can create and change breeds: A) Conscious selection of desirable characteristics; B) Breeding of "the best" specimens, leading unconsciously to improvement of the breed.
Within a species there are many varieties, generally with similar traits linking them together. Within each genus there are species, many of which group into subgenera based upon common traits. Point: there are lots of common traits!
There's a struggle for survival in nature, as evidenced by the fact that many more individuals of a species are born than survive through long lifetimes. The struggle is between individual members of a species as well as between members of competing species. There are 4 factors which determine population size: 1) competition with other species that take up valuable resources, 2)predators, 3)climate, and 4)epidemic (which usually occurs with overpopulation). In order for a species to thrive, it often needs a large population--thus reducing inbreeding and allowing for variability. Competition is often strongest between species of the same genus because these species have similar characteristics--they require similar resources and respond to threats in similar ways.
I finished chapter 1. As I've mentioned on other threads, I got immersed in a home renovation project this month, which is a good thing in the long run, but in the short run has meant very little reading aside from magazines and a RL event. The plan at the moment is to wrap up March with brief reviews, and begin April with renewed vigor.
Darwin starts by describing how nature might use variation to select traits that are desirable. Nature will kill off individuals which are least fit, leaving individuals which are more fit. This process can be repeated over generations for thousands of years, thus leading to a population which is well-suited to its environment. Sexual selection, on the other hand, is a result of the struggle between males for mates. Although the least fit individuals don't die, they produce less offspring and are effectively kicked out of the genetic pool. Darwin suggests that even hermaphroditic species have sexual recombination (which is more true than he knows!)
There can be variation in color, fur thickness, etc. based upon climate and amount of light. Use and disuse can also impact selection of traits. He makes the very astute observation that the selection in one trait leads to correlative changes in other traits. This is an early hint about selection of nearby genes to desirable trait (like malaria/sickle cell anemia).
Why aren't there innumerable transition forms instead of distance species? Transitional ("imperfect") varieties die off, leaving selected varieties. Why not find these transitions in the fossil record? Because the fossils could only be formed under specific conditions, and these conditions weren't met for thousands of years at a time. He also discusses how organs can have changed function throughout time, or how they may have lost their function altogether.
I'm not forgetting or ignoring, just have too many items on the agenda and LT has dropped in priority while I get RL under control. Glad you're continuing to read. I'll get there...
On the topic of Richard Dawkins, while I find Creationism frightening, I think the man has, on this topic, done science a big disfavour with his militant preaching.
I should probably try to get over my dislike of his writing style and give The God Dilusion a read, so I can opine about it reasonably, but, while I am in no way religious, it's my opinion that a true scientist should question everything and while there are facts I think we can be pretty certain of, we should always be willing to listen to a new argument which might (however improbable) bring new information to light. No one can know everything.
This said, absolutely, more scientists need to come out of the woodwork to explain what they do understandably, there have been far too many badly reported scientific stories that have caused real damage (the MMR vaccine scare anyone?)
Re Dawkins, that's exactly why I read The God Delusion last year. I wanted to comment on reviews based on what I'd seen of Dawkins elsewhere, grrrrrr... Gist of my reaction: For a scientist, Dawkins is awfully fuzzy on the definition of religion. He opposes, legitimately and humorously, the fundamentalist subset, and acknowledges the existence of non-fundamentalists who accept modern science, but he seems bewildered what such people might get from religion, and sees them as giving cover to irrational thinking. When he speculates on how religion might have evolved, it gets entwined with all manner of human foibles. (http://www.librarything.com/topic/115684#2821837, http://www.librarything.com/topic/115684#2845017)
This said, absolutely, more scientists need to come out of the woodwork to explain what they do understandably, there have been far too many badly reported scientific stories that have caused real damage (the MMR vaccine scare anyone?)
Tons o' science blogs these days, and many complaints about science reporting. My impression is the gap between professional journals and general public is narrowing, and this is hopefully putting some pressure on newspapers and magazines and TV.
I, for one, am planning to make it a 6 month project for myself.
I still haven't read anything by Dawkins, sometime later this year or next year maybe.
>34 flissp: Don’t worry about starting late. I stopped after Chapter 6 because I became busy with other things, and now that I’m about to start Religion Explained I imagine I won’t move very fast on On the Origin of Species. We’ve got plenty of time.
Rachel is way ahead than most of us I think. Haven't seen Ren in quite a while, wonder how she is faring with the book.
qebo, thanks for the God Delusion summary - will follow those links at some point when I'm not at work. I probably won't get to the book for a good long time - it's not a book I particularly want to read (I dislike his writing style intensely quite beside anything else), more one that I feel I should.
Re science reporting, you're quite right, it's definitely improved leaps and bounds in recent years and blogs have, I'm certain, had a big influence on this and are a great step in the right direction, but there's still a long way to go - particularly in more general media (radio/tv/newspapers/magazines).
#37 The_Hibernator, I think I probably agree with you re Dawkins, if from the opposite angle!
...and good good. I'll bung it on my bedside table tonight, so that I don't forget about it this time!
The Struggle for Existence is used in "a large and metaphorical sense" that includes interdependence of organisms, dependence on features of the environment such as climate, competition with nearby nearly identical organisms. More individuals are produced than can survive; otherwise a single pair of any organism would rapidly fill the earth. This is true for thousands of seeds or eggs, or for a single offspring; if offspring can be protected, then fewer need to be produced. An individual may be checked at any stage of its existence, and we are often ignorant as to causes. Here is presented a sweet experiment that gives a glimpse of Darwin as meticulous observer: A 2' x 3' plot of ground is cleared, and seedlings are marked as they appear. Of 357 that appeared, 295 were destroyed, mostly by slugs and insects. Another example: On a large estate with barren heath, a portion was fenced and trees were planted. 25 years later, the contrast was significant. The enclosed areas had different proportions of heath plants, and other species had appeared, plants not found on the heath and birds attracted to insects. In another region, nothing had been done except to fence areas so that grazing cattle could not eat tree seedlings, with similar effects. Though plants and animals "are bound together by a web of complex relations", the struggle is most severe between individuals of the same species, which occupy the same space and require the same food and are exposed to the same dangers. Variations within species exist, this is not in dispute however they may have arisen, and it is the variations more favorable to survival that increase in proportion. "The structure of every organic being is related, in the most essential and often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has to escape, or on which it preys."
In previous chapters, Darwin set the stage. In this chapter, he describes natural selection in detail. It is "the preservation of favourable variations and the rejection of injurious variations", with a "fluctuation element" of variations neither favourable nor injurious. Extreme variations aren't necessary; small variations can add up over time. Consider the changes produced in a comparatively short time by domestic selection. Nature operates at the scale of geologic periods; no wonder its productions "bear the stamp of far higher workmanship". Along with natural selection is sexual selection, which is not a struggle for existence, but a struggle between males for females, "less rigorous than natural selection" and resulting in fewer offspring. Hypothetical examples of natural selection follow. From observation and the experience of breeders, it seems probable that no organism self-fertilizes for an eternity, even hermaphrodites; crosses between individuals of different varieties tend to increase vigor, while crosses between too similar individuals tend to diminish vigor. The advantage of "mongrelization" explains, for example, why plants with structures that would seem allow self-pollination, instead separate them in time or need insects to trip the mechanism. "There is no place in which all organisms are so perfectly adapted that no improvement is possible; we can see this when foreign organisms take over."
I actually read chapter 4 immediately after chapter 3, and documented only this far. It's a long chapter. Now that three weeks have gone by, maybe it's time to just go with what I've got and move on.
I find that's often best. :)
"I have hitherto sometimes spoken as if the variations ... had been due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation." We don't know how much variation to attribute to "the accumulative action of natural selection" and how much to "the conditions of life" such as climate and food. In domesticated animals, it appears that "use" strengthens features, "disuse" diminishes them, and such modifications are inherited. In nature, similar. For example, if wings are not used, birds or beetles may become wingless. Of the beetles on Madeira, some have enlarged wings and some have reduced wings, and this is compatible with natural selection. "As with mariners shipwrecked near a coast, it would have been better for the good swimmers if they had been able to swim still further, whereas it would have been better for the bad swimmers if they had not been able to swim at all and had stuck to the wreck." Burrowing rodents may have eyes covered by skin and fur. Crabs living in caves may have stalks for eyes, but not eyes. The loss of eyes is attributed to disuse. Organisms are so integrated during growth that when one part is changed, other parts are changed also. Modifications that are good for larvae may affect the structure of adults. Homologous parts, such as front and hind legs, vary similarly. The shape of hard parts, such as the pelvis, affects the shape of soft parts, such as the kidneys. The correlation may be obscure, such as blue eyes and deafness in cats. If a feature becomes less useful, then any reduction in its development is "seized on" by natural selection, so that nourishment is available for other features. A feature developed to an extraordinary degree, in comparison with allied species, is presumed to be important, and tends to be highly variable. Why would this be? This feature has undergone extraordinary modification, implying variability over a long duration until the feature has been fixed. The points in which all species of a genus resemble each other are called generic characters. The points in which species of the same genus differ are called specific characters.
"Long before having arrived at this part of my work, a crowd of difficulties will have occurred to the reader. Some of them are so grave that to this day I can never reflect on them without being staggered; but, to the best of my judgment, the greater number are only apparent, and those that are real are not, I think, fatal to my theory."
(1) If species have descended by small changes, why don't we see small differences everywhere, but instead see well defined species?
Observing species, we tend to find that the regions of two representative species are much wider than the region between them. Each creature is dependent on many others, not just on gradually changing physical conditions between one region and another. So a variety that links two other varieties exists in smaller numbers, and tends not to endure.
(2) How is it possible to form one animal from another with different structure and habits? How could an animal in a transitional state have subsisted? If we see an organism with features well suited to its current environment, it will have supplanted organisms with features less well suited, and is not necessarily the best it could possibly be under all conditions. As features change, habitats may change, or as habitats change, selection of different features may follow. Consider the eye. It is not so immediately apparent how such a complex feature could have been formed by natural selection, but we can observe what gradations are possible in existing species. Among the vertebrates, there are few gradations, so we have to go back further. A series of gradations begins in the Articulata, with an optic nerve coated with pigment, and from here numerous structures of increasing complexity can be found. "It is scarcely possible to avoid comparing the eye to a telescope. We know that this instrument has been perfected by the long-continued efforts of the highest human intellects; and we naturally infer that the eye has been formed by a somewhat analogous process. But may not this inference be presumptuous? Have we any right to assume that the Creator works by intellectual powers like those of man?" There are cases of an organ performing different functions, so that it could be selected for the improvement of one function alone. There are cases of two organs performing similar functions, for example fish with gills that breathe air dissolved in water and swimbladders that breathe free air, so one organ could be modified to perform the function by itself leaving the other available for another purpose; the swimbladder is homologous with lungs. And there are cases where similar features appear in organisms that are only distantly related, for example electric organs in fish, and luminous organs insects. "I am inclined to believe that in the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor." We are "profoundly ignorant" of the causes of variations, but we can see them occur in the process of domestication. "It is generally acknowledged that all organic beings have been formed by two great laws -- Unity of Type, and the Conditions of Existence." Unity of Type is explained by unity of descent. Conditions of Existence is explained by the principle of natural selection.
(3) Can instincts be modified by natural selection?
(4) Why are crosses between species sterile, and crosses between varieties fertile?
(1) and (2) are discussed in this chapter, (3) and (4) in the next.
ETA: But I don't think I'll get much further for the moment, so you'll pass me soon.
Rebecca: You are just 4 Chapters behind me!
qebo: You are still a couple of Chapters ahead of me!
Rachel is still leading the pack on this one.
Instinct is not defined; “several distinct mental actions are embraced by this term”. Instinct might be an action performed by an animal without experience, or performed by many animals in the same way, without their knowing its purpose. Instinct is as important as body structure for survival, and natural section can act on slight profitable variations, so we ought to find gradations leading to complex instincts. An experiment with ants and aphids; “each species takes advantage of the instincts of others”. Three examples: cuckoo laying eggs in the nests of other birds, ants enslaving other ants, bees constructing honeycombs. Cuckoo: The cuckoo lays eggs at intervals of two or three days. This can extend the process of raising young, or leave eggs unincubated while feeding hatched chicks. This is the situation of the American cuckoo. If the European cuckoo occasionally laid an egg in another bird’s nest, and the young were more vigorous as a result, the habit would be strengthened. Ants: “I tried to approach the subject in a sceptical frame of mind, as any one may well be excused for doubting the truth of so extraordinary and odious and instinct as that of making slaves.” Formica sanguinea makes slaves of F. fusca, a smaller species. When the nest is disturbed, both masters and slaves defend the nest and rescue the larvae and pupae. If the pupae of other species are presented, F. sanguinea will pick up F. fusca, but not F. flava, another smaller species. Other ants that do not make slaves will also carry away pupae of other species on occasion. If pupae originally taken as food developed to maturity and their work instincts were useful to the colony, the habit of bringing them to the nest would be strengthened. Bees: At one end are the humble-bees, which make separate and irregular cells of wax. At the other end are the hive-bees, with a double layer of hexagonal cells. In between are, for example, Melipona domestica of Mexico, which make a nearly regular comb of cylindrical cells for hatching young, and large nearly spherical cells of wax for honey. If the spheres were completed they would break into each other, but instead the wall where they meet is flat, and the thickness of a single wall, so wax is saved. A slight modification of this instinct would result in hexagons. Darwin experimented with hive-bees: He placed a thick strip of wax between two combs. The bees began to excavate basins, but stopped when the basins intersected, and switched to building walls. He placed a thin strip of wax between two combs. The bees began to excavate basins, but stopped before the basins broke through, leaving flat surfaces between basins on opposite sides. “The work of construction seems to be a sort of balance struck between many bees, all instinctively standing at the same relative distance from each other, all trying to sweep equal spheres, and then building up, or leaving ungnawed, the planes of intersection between these spheres.”
What about, for example, ant communities with females that are sterile and also differ greatly from the parents? Throughout nature are differences of structure correlated to either sex, or certain ages or stages, so why not differences of structure correlated to sterility? But how do these correlated modifications accumulate by natural selection? Natural selection “may be applied to the family, as well as the individual.” “Thus I believe it has been with the social insects a slight modification of structure, or instinct, correlated with a sterile condition of certain members of the community, has been advantageous to the community: consequently the fertile males and females of the community flourished, and transmitted to their offspring a tendency to produce sterile members having the same modification.” But castes of sterile ants are distinct from each other, as well as from fertile ants. Inspecting ants from a nest, it has been found that the extreme forms may be more numerous but can be linked by individuals of intermediate size or features; the extreme forms may have been most useful to the community. “As ants work by inherited instincts and by inherited tools or weapons, and not by acquired knowledge and manufactured instruments, a perfect division of labour could be effected with them only by the workers being sterile; for had they been fertile, they would have intercrossed, and their instincts and structure would have become blended.”
Two classes of facts tend to be confounded: “the sterility of two species when first crossed, and the sterility of the hybrids produced from them.” “The distinction has probably been slurred over, owing to the sterility in both cases being looked on as a special endowment, beyond the province of our reasoning powers.” “...in order to prevent confusion of all organic forms.” Pure species have reproductive organs intact, but when crossed may produce few or no offspring. Hybrids may have functionally impotent reproductive organs. Evidence is more from plants than animals because of the difficulties of breeding in captivity. The fertility of varieties is as important as the sterility of species, and seems to make a clear distinction between varieties and species. The trouble is the circularity; individuals are declared varieties of the same species if fertile, and separate species if sterile. The sterility of species when crossed is graduated; it is “most difficult to say where perfect fertility ends and sterility begins.” The fertility of hybrids often decreases in the first few generations, but this may be because of close interbreeding; “hybrids are seldom bred by experimentalists in great numbers.” There is no determination of what differences prevent two species from crossing. Some species that appear very different can be crossed. There is often a difference between reciprocal crosses, i.e. the male of one species and female of the other, versus the female of one species and male of the other. Some species can be crossed easily but produce sterile hybrids. Some species can be crossed only with difficulty but produce fertile hybrids. The complexity or obscurity of the rules suggests that sterility is not a special quality for the purpose of preventing confusion of species, but rather is “incidental or dependent on unknown differences, chiefly in the reproductive systems.”
If the theory of natural selection is true, then the number of intermediate and transitional links must be “inconceivably great”. “Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain.” “It is highly important for us to gain some notion, however imperfect, of the laps of years. During each of these years, over the whole world, the land and the water have been people by hosts of living forms.” He presents one example where the sea, wearing away a cliff at a rate of one inch per century, would take over 300 million years to produce the formation. “We continually forget how large the world is, compared with the area over which our geological formations have been carefully examined.” Geological formations are intermittent and separated by intervals of time. Organisms are preserved “during periods of subsidence, but only where the supply of sediment was sufficient to keep the sea shallow and to embed and preserve the remains before they had time to decay.” Still, in any one formation, why don’t we see gradations of species between its bottom and top? The duration of a geological formation may be shorter than the period necessary for one species to change to another. Animals move, so the appearance or disappearance in the middle of a formation doesn’t mean creation or extinction. A perfect gradation requires a thick deposit, accumulated over a long period, with subsidence counterbalanced by sediment to keep approximately the same depth, to keep the same conditions for the same species. It is the creatures with wider ranges, wider than geological formations, that tend to have more varieties, which give rise to more species.
There is more, but I’m not so terribly interested in geology, and the record is less imperfect 150 years later...
Does the geological succession of organic beings accord with immutability or gradual modification? Between consecutive geological formations, forms of life change, though not by exactly the same amount. Groups of species, genera and families, follow the same general rules as species. The variability of one species is independent of the others and depends on complex contingencies, not on a fixed law of development. The same agencies that check population increase, also cause decrease and extinction. Once a species has disappeared, the identical form never reappears. The paleontological record shows that marine life forms have changed in parallel throughout the world, as dominant forms have spread. The forms of any period are intermediate between earlier and later forms. All fossils can be classified in or between existing groups; the system is less perfect if attention is confined to either living species or extinct species, than if it includes both.
The distribution of similar and different organisms in cannot be accounted for by climate or other physical conditions. A fundamental division is between Old and New worlds, and either alone includes a wide range of conditions. Large areas of South Africa, South America, and Australia have very similar conditions, but the flora and fauna are very different. Barriers between regions correlate with differences in organisms; this may be land separated by water, or water separated by land. The distinct marine animals of the eastern and western shores of South America are separated only by the narrow isthmus of Panama. Within the same continent or sea, however, is affinity between organisms even when conditions are very different. Some relationships can be accounted for by geological changes over time, e.g. connections between land masses that are now separate, or the extension of circumpolar regions during glacial periods.
Although lakes and rivers are separated by land barriers, many fresh water species have enormous ranges, with allied species throughout the world. If short and frequent migrations from pond to pond are necessary for survival, then wider dispersal follows. Birds disperse plant seeds, and possibly the eggs of some animals. The number of species on islands is generally fewer than the number of species on equal areas of continents, but the proportion of endemic species (found nowhere else in the world) is higher. Oceanic islands may be deficient in certain classes, such as mammals; their place is taken in the Galapagos by reptiles and in New Zealand by giant wingless birds. There is no confirmed instance of a terrestrial mammal inhabiting an oceanic island more than 300 miles from a continent or continental island, but there are many examples of aerial mammals such as bats. The relationship between the depth of water separating an island from the mainland, and the presence of allied species, can be explained by land connections resulting from changes in depth. The inhabitants of islands are more similar to the inhabitants of the nearest mainland, than to each other; e.g. Galapagos to America, and Cape de Verde to Africa.
All organic beings can be classified in groups under groups. This didn’t have to be so; when forms were categorized by similarities, they could have fallen together by habit or habitat, but they did not. The external similarities of, for example, a whale and a fish, are merely “adaptive and analogical characters”. The physiological importance of an organ does not determine its value for classification. What matters is the prevalence of a feature. For this purpose, the embryo becomes significant. The “community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation”. The natural system of classification is genealogical. This has always been the case with varieties, which are known to have descended from species; whatever features are most constant are are used for classification. Included in a single species are the forms of the two sexes, even if they differ significantly, and the larval stages, because they are known to have genealogical connection. Several guidelines for comparison have been followed by the best systematists in choosing features for comparison, e.g. least likely to have been modified by the conditions of life, or rudimentary structures. Adaptive or analogical resemblance may be of utmost importance to an organism, but of no value to a systematist.
The resemblance of members of the same class, independent of habits, is the subject of morphology. “This is the most interesting department of natural history, and may be said to be its very soul. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?” ”We see the same great law in the constructions of the mouths of insects: what can be more different than the immensely long spiral proboscis of a sphinx-moth, the curious folded one of a bee or bug, and the great jaws of a beetle? – yet all these organs, serving for such different purposes, are formed by infinitely numerous modifications of an upper lip, mandibles, and two pairs of maxillae.” In homologous organs, with parts may change in form and size, but remain always connected in the same manner. As the same part in different members of a class can be compared, different parts in the same individual can be compared. In vertebrates, the anterior and posterior limbs are homologous, and the skull bones are homologous with the vertebrae. In flowers, the sepals, petals, stamens, and pistils are homologous with the leaves. “How inexplicable are these facts in the ordinary view of creation!” But these facts make sense in the theory of natural selection. Vertebrates have repetitions of segments. Plants have repetitions of leaves. ”We have formerly seen that parts many times repeated are eminently liable to vary in number and structure; consequently it is quite probable that natural selection, during a long-continued course of modification, should have seized on a certain number of the primordially similar elements, many times repeated, and have adapted them to the most diverse purposes.”
Some organs that become different in adults, are exactly alike in the embryo. The larvae of moths, flies, and beetles resemble each other more than the mature insects. The points of resemblance may have no direct correlation with the conditions, e.g. the arteries near branchial slits of a mammal in the womb, the egg of a bird in a nest, the egg of a frog under water. However, larvae that must provide for themselves may differ as much as adults, and successive stages may differ from each other. What matters with variations is not when they are caused, but when they appear. Breeders often cannot see the merits of an animal until it has developed. Puppies of different breeds, for example, are more closely similar in proportion than adult dogs. There is evidence that at whatever age a variation appears in the parent, it tends also to appear in the offspring. With successive slight modifications, it can diverge at later ages.
Rudimentary organs are common in nature, and some are quite curious, e.g. teeth in fetal whales. Wings are for flight, but may be incapable of flight in some birds or beetles. An organ that serves for two purposes may cease to be used for one and remain efficient for another, or become unusable for its original purpose and be used for another. When homologies are traced among members of a class, rudiments are often found. Rudimentary organs tend to be of relatively greater size in embryos than in adults. In the theory of natural selection, disuse is the main agency, e.g. eyes of animals that inhabit caves, or wings of birds that inhabit oceanic islands. As an organ becomes unused or even injurious by change of habit or habitat, the principle of economy saves its material for other purposes. ”Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in pronunciation, but which serve as a clue in seeking for its derivation.”
This chapter is mostly a summary of previous chapters.
Why have eminent naturalists rejected the idea of mutability of species? ”The belief that species were immutable productions was almost unavoidable as long as the history of the world was thought to be of short duration.” And we are slow to recognize great change when we do not see the steps; this was true for geology too. ”It is so easy to hide our ignorance under such expressions as ‘the plan of creation,’ ‘unity of design,’ etc., and to think that we give an explanation when we only restate a fact.” Several naturalists have proposed that some species were independently created, and others were produced by variation, but are not clear on which is which. ”These authors seem no more startled at a miraculous act of creation that at an ordinary birth.” Were these species created as seeds or eggs or as adults? ”Though naturalists very properly demand a full explanation of every difficulty from those who believe in the mutability of species, on their own side they ignore the whole subject of the first appearance of species in what they consider reverent silence.” From how many progenitors have the species evolved? Surely no more than a few, and possibly both plants and animals have descended from a single prototype. All living creatures, plants and animals, have common chemical composition, cellular structure, and laws of development.
What does the future hold? As the theory of natural selection becomes accepted, systematists will be relieved that there is no need to determine whether a variation is or is not a separate species, and will “be freed from the vain search for the undiscovered and undiscoverable essence of the term species”. ”The other and more general departments of natural history will rise greatly in interest. The terms used by naturalists of affinity, relationship, community of type, paternity, morphology, adaptive characters, rudimentary or aborted organs, etc., will cease to be metaphorical, and will have a plain signification.” ”A grand and almost untrodden field of inquiry will be opened, on the causes and laws of variation, on correlation of growth, on the effects of use and disuse, on the direct action of external conditions, and so forth.” ”Our classifications will come to be, as far as they can be so made, genealogies; and will then truly give what may be called the plan of creation.”
The "sequel" has some good reviews and some really bad reviews,
i. "His writing is, according to one's taste, lightened or made tedious by his arch remarks, tangents, and lurid tabloid examples (Eighty-year-old woman eaten by dog pack! Carrion crows eat lambs' eyes!) I think Natterings in Natural History would be a better title.
ii. "If (many) professional biologists don't read the Origins, ordinary people who read it are left to themselves in deciding which of Darwin's views have been abandoned by science. Jones bridges this gap, brings more examples and adds the relevant science. It is not a review of the current state of evolutionary biology but a useful, much needed companion to Darwin's book."
So, you see, I am confused, will have to think some more if I want to pursue this book, if you do read it in the meantime, I will bank on your review to solve the dilemma for me.
#73 You are STILL only 6 chapters behind me, not too late to start :)
I am sure everyone reading this review knows what the book would generally be about, and therefore, I would like to discuss some other features, which struck me. The book has a strong defensive undercurrent, through which Darwin at times is more concerned with defending his position than asserting his viewpoint. Darwin's tone, at places, where there is little proof to propagate his theory, is almost apologetic. Then he writes that many naturalists have come to terms with natural selection, while ridiculing others, who may still believe in independent creation of species.
Another most interesting observation was the glaring and most obvious absence of any definitive statement on the evolution of humans - a clear indication on Darwin's lack of willingness to rake up such a sensitive issue, his work being controversial enough as it already was. He touches upon this topic most superficially, carefully sandwiched in a para about Herbert Spencer and human psychology, "In the future I see open fields for far more important researches. Psychology will be securely based on the foundation already well laid by Mr. Herbert Spencer, that of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history." Darwin revisited this topic 12 years later, in his The Descent of Man, by which time, the populace probably had enough time to digest and accept the basic tenets of evolution.
A timeless book, even if now dated.