Darwin’s Good Book

Darwin’s Good Book          

 

A good way to begin a book report on one such as On the Origin of Species by Charles Darwin would be a synthesis of his major points and then a summary of the remaining chapters. The reason for this organization is that the author in this case tends to be exhausting in his descriptions.  This is not to say that he is a windbag, just that he needed to compensate for the rightly anticipated reactions of his fellow nineteenth century naturalists, not to mention the Christians.

            Darwin begins the book by drawing attention to artificial selection by way of breeding domestic animals.  This is a good way to introduce the subject of evolution by way of natural selection.  The average person at the time the book was written and even scientists at the time were skeptical of the idea, so he seems to ease the reader into the idea by showing examples of genetically influenced breeding the average person can readily see.  Selecting and breeding domestic animals is a time tested practice with more or less predictable results.  It effectively makes a well known point about heritability and applies it to the entire world and all living things in it.  He also mentions that many of the desirable or undesirable traits are a result of location as well as the human selection of mates.  There is an ambiguity about the concept of species because Darwin is comparing his definition of the words to many other different definitions.

            One of the most important concepts that is introduced early on is the idea that all organisms would produce offspring at a geometric rate if they all survived to maturity.  If 100% of any one species offspring survived long enough to reproduce, they would overrun the world very rapidly.  This leads us to conclude that only a small percentage of organisms born survive long enough to procreate.  The question this raises is why some survive where others die.  The answer is that some are better equipped to survive, hence the often misused notion of survival of the fittest. Two other observations must be taken into account before delving into natural selection. The first is that the overall population of a given species is relatively static within its natural confined borders. This observation must exclude human involvement because if a land animal is brought from one continent to another by boat, it has gone beyond the natural borders through no fault of its own. The second observation is that resources are also relatively static and limited and so, put simply, there are more animals than there is food to feed them all. Luck has nothing to do with it

            This survival of the fittest idea can be narrowed down into the theory of natural selection.  The competition for resources is what keeps the populations static and non-increasing. They die because something else got to the food first or because something else killed it and ate it.  There are 4 kinds of competition, competition within a species for the same resources, competition between similar species for the same resources, competition between predator and prey for survival, and competition between males for the opportunity to procreate with the most desirable female.  The first three kinds of competition are challenges as to who will live long enough to procreate and the fourth is a challenge to pass on genetic material.  Darwin goes into detail concerning the competition for a mate as a way of natural selection.  The kind of competition that involved a physical or violent confrontation is a way of ensuring the strongest survive. The kind of competition like birds often engage in results in characteristics that often have no other purpose than to attract a mate.

            Every organism is slightly different from all others in the species and these small differences can often be transmitted to the next generation. The ram with the slightly harder head that got the lady ram to have his baby rams will pass on some of that hardheadedness to the kids.  The slightly faster squirrel that got to the food before his brother will live and have other squirrels, while his brother will starve to death.  The winners get to pass their genes on. 

            This inheritable variation happens very slowly and we can infer from this that luck has nothing to do with the morphological characteristics of a species.  The reason is that favorable characteristics have to accumulate in a gene pool before they become significant as an advantage or guaranteed as an inheritable characteristic.  When these traits do become significant, the portion of the species that has the characteristic will dominate the species and the earlier version will often die out.  People wonder what happened to the Neanderthals but I’m pretty sure we killed them.

            Darwin emphasizes several times that because we are largely ignorant of how organisms exist relative to each other and the surroundings, we can not dismiss any characteristic as useless or solely decorative.  He makes the assumption that all variations are or were at some point useful.  Natural selection also leads to variation within a species that can lead to a new species instead of the extinction of the earlier version.  For this reason Darwin proposes that current living organisms all descended from a common ancestor and makes an analogy to a tree where some buds branch off and form new limbs while others die and grow no further.  It is interesting to see Darwin articulate this concept of heredity because currently it can be easily proven using DNA while Darwin relies on several hundred examples to prove his point.  It can be confusing though because the idea of heredity is presented to be at odds with variation.  He has the notion that heredity might act to correct the variations.  It is easy to understand how this might have been a point of conflict because he was only able to observe a limited number of generations. When variations are not soon apparent in successive generations one could draw the conclusion that there is a force acting against inheritable variation.

            This is the general theory of evolution and much of the remaining pages are devoted to explanations of various natural processes that might support or run contrary to the theory. Examples of these include the problem of hybridization which makes the male-male competition of natural selection inapplicable.  He also devotes a good deal of time to an examination of the geological record.  In this discussion he points to the fossil record that supports demonstrable variations on species he believes to be ancestors of modern organisms.  He demonstrates the difficulty and unlikelihood of producing very convincing evidence because of the imperfect fossil record.  This discussion is used in part to explain the similarities found around species on different continents, the reason being a common ancestor living at a time when the continents were connected.

            Once the theory is understood, the most import point to remember is that “natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modification; it can act only by short and slow steps.” (p.471)

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