Drawing from my own reading library, this book a little like Adam Smith's Wealth of Nations in that the author is taking personal observations and anecdotes and developing a broader hypothesis as to how things work and how we got to where we are today. Many of the anecdotal observations and hypotheses have since been proven as false or mistaken, and we now know more about what was observed than the author possibly could have at the time, but the broader implications and the core of the central hypothesis remain intact.
Darwin spends early part of the book discussing the difference between variations and species. Modern biological classification had not been completely developed at the time of publication. Genealogy was basically undeveloped, or is perhaps not Darwin's strong suit. His religious detractors at the time argued that species were immutable and that the geological record was perfect-- everything that could be known about the history of the earth was essentially already evident. I do not know how widespread the belief was at that time, but creation scientists today acknowledge mass migration, extinction, and "macroevolution," that from one species or phylum can come many different varieties.
In Chapter 5, Darwin opines on why zebras have stripes in a greater context of how unique traits evolve in offspring and how offspring sometimes revert to the characteristics of their predecessors. There was no agreed-upon model of heredity back then. Scientists are still determining why zebras have stripes.
Chapters 6 and 7 are interesting as Darwin pivots to address possible criticims of his theory of natural selection. development of organs and the imperfections in the fossil record. He admits that it's hard to believe that something as incredibly complex as the eye developed gradually, but contends that it is not impossible. He contends that whale's lungs developed from an organ that was originally a swim bladder. Since vertebrates have lungs, we must have all evolved from organisms that had swim bladders-- ie: sea-dwelling creatures:
"The illustration of the swim bladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely, flotation, may be converted into one for a widely different purpose, namely, respiration. The swim bladder has, also, been worked in as an accessory to the auditory organs of certain fishes. All physiologists admit that the swimbladder is homologous, or “ideally similar” in position and structure with the lungs of the higher vertebrate animals: hence there is no reason to doubt that the swim bladder has actually been converted into lungs, or an organ used exclusively for respiration. According to this view it may be inferred that all vertebrate animals with true lungs are descended by ordinary generation from an ancient and unknown prototype, which was furnished with a floating apparatus or swim bladder."
In Chapter 7 Darwin writes that one discovery that would demolish Darwin's theory is if altruistic behavior were to be found in an organism-- if one species acted simply to benefit another. This would be impossible under natural selection since each species has developed by focusing on adapting solely on its own survival in the "battle for life." Some have purported that the behavior of one type of ant which serves as a slave to another type are an example of this. Darwin maintains that the enslaved variety is smaller and weaker, and kept alive by their masters due to their usefulness, and therefore acceptance of the slavery is necessary to their survival.
One wonders, however, at the symbiotic relationships of many species. For example, I read an article recently about how botanists researching fungi have changed their belief in their relationship with trees:
“The new theory pictures a more business-like relationship among multiple buyers and sellers connected in a network,” Franklin said in a press release. Instead of being a cooperative trade of carbon and nitrogen between organisms, trees are forced to export large amounts of carbon in order to unlock nitrogen stores from the fungi."
The fact that mating behavior-- taking two to create offspring-- has evolved among so many species would seem to be problematic to natural selection. Wouldn't it be more efficient for survival if one could reproduce asexually with a relatively small gestation time? Why haven't the majority of species evolved that way? It seems that there are benefits to mating beyond reproduction. There is strength in symbiotic communal behavior, as Darwin gives the example of ants and hive bees. Since this behavior is so widespread, one can deduce that it is closer to the "perfection" eventually achieved by natural selection relative to the lower-order ancestors' way of producing.
In Chapter 9 and onward, Darwin deals with the imperfection of the fossil record. We are missing transitional forms at every level to verify his theory. In some layers or time periods, species appear which do not appear in the previous time period. This would seem to suggest creation rather than systematic evolution. Darwin's response to such a criticism is :
On this doctrine of the extermination of an infinitude of connecting links, between the living and extinct inhabitants of the world, and at each successive period between the extinct and still older species, why is not every geological formation charged with such links? Why does not every collection of fossil remains afford plain evidence of the gradation and mutation of the forms of life? Although geological research has undoubtedly revealed the former existence of many links, bringing numerous forms of life much closer together, it does not yield the infinitely many fine gradations between past and present species required on the theory, and this is the most obvious of the many objections which may be urged against it. Why, again, do whole groups of allied species appear, though this appearance is often false, to have come in suddenly on the successive geological stages? Although we now know that organic beings appeared on this globe, at a period incalculably remote, long before the lowest bed of the Cambrian system was deposited, why do we not find beneath this system great piles of strata stored with the remains of the progenitors of the Cambrian fossils? For on the theory, such strata must somewhere have been deposited at these ancient and utterly unknown epochs of the world's history. I can answer these questions and objections only on the supposition that the geological record is far more imperfect than most geologists believe.
Much has been undiscovered, much may lay under the oceans, and many layers may be compressed due to constantly having more sediment deposited.
"Authors of the highest eminence seem to be fully satisfied with the view that each species has been independently created. To my mind it accords better with what we know of the laws impressed on matter by the Creator, that the production and extinction of the past and present inhabitants of the world should have been due to secondary causes, like those determining the birth and death of the individual. When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Cambrian system was deposited, they seem to me to become ennobled... There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved."
Darwin's arguments still did not answer the question for me as to how the eye and other organs developed. How did the original cells know that that there were light and sound waves from which information could be gleaned if a complex structure were developed to capture it?
Darwin either does not think about or chooses not to write about the ethical implications of his work. If we are not made in the image of God, do we have inalienable rights? Why should there be consequences if one murders another? The natural order is always engaged in a "struggle for life," and the end result is that it is leading us toward evolutionary "perfection." But what aspects of our society and behavior are evolutionary artifacts that will eventually die out and which are essential for our survival?
I give this book 4 stars out of 5. Everyone should read it as it's a classic, definitely one of the most influential books on the 19th, 20th, and 21st centuries. I plan to read Michael Behe's Darwin's Black Box before the end of the year.
On another note, I listened to this book on the freely-available audio files on Gutenberg. The text was read by a computer, each chapter alternated between a male and a female voice. This made it hard to listen to at my usual 2X speed as the cadence was a bit...unnatural...and some of the pronunciations were butchered. But I found it definitely doable.