Darwin On the Origin of Species Chapter 3

The third chapter of Darwin’s wonderful work is “Struggle for Existence” and is another short but info filled chapter.  He’s focusing on how struggle bears on natural selection.

Darwin once again points out the importance of variation:

Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.  The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man’s power of selection. (64)

The struggle for life is something Darwin found fascinating, yet something that humans tend to easily forget.  We don’t bear in mind that everything, even if it appears to be in a state of abundance and health, deals with struggle constantly.  On a sunny Spring day, you may see green grass and blooming flowers, several species of singing birds and various mammals relaxing in the sunshine.  What you may be missing is the birds’ constant crunching on insects.  Maybe, you’re not noticing that the cozy mammals just had a nice midday meal or the stunted plants in between the healthy specimens.  Darwin insists that without the understanding of the struggle for existence, we cannot have a full understanding of nature and several biological facts.  Darwin also points out that what he means by “Struggle for Existence.”  He doesn’t just include physical fighting and bloody death in his definition.  He includes interdependence and the success in leaving offspring, along with the struggle against the elements (65). 

Darwin spends several pages discussing the struggles of living beings.  He also discusses population growth and checks on that growth.  He has a wonderful example of the delicate balance in nature and the fact that even a small change can greatly influence populations (pages 72-4 Scotch Fir).  This struggle is ongoing, but as Darwin points out, it is so well balanced that we barely notice it.  We are amazed when we hear of an extinction event.  Or, at least, Darwin was.  It’s become quite common place nowadays. 

The struggle for existence can seem rather daunting and downright depressing at times.  However, we shouldn’t be too disheartened.  I’ll let Darwin’s final chapter comments sum up:

All that we can do, is to keep steadily in mind that each organic being is striving to increase at a geometrical ratio; that each at some period of its life, during some season of the year, during each generation or at intervals, has to struggle for life, and to suffer great destruction.  When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.  (78-9)

Darwin On the Origin of Species Chapter 2

I'm finally posting another chapter summary for On the Origin of Species 2009 Penguin Classics edition (it's taken me long enough).

Chapter 2 is called “Variation under Nature” to differentiate what Darwin discussed in the previous chapter, “Variation under Domestication.”   This chapter is short but packed full of info.  Darwin takes the ideas from the first chapter and applies them to the natural world of undomesticated plants and animals. 

The chapter starts off by discussing the nature of species.  There’s not a clear cut line between different species as many people suppose.  There are lots of gray areas, and scientists during Darwin’s time, and even today, argue about where one species ends and another begins.  Sometimes one plant or animal can be defined as a separate species by one scientist only to be defined as a variety (of another species) by a different scientist.  This can get confusing to the lay person.  You have to keep in mind that we’re looking at constant transitions and changes in living things as opposed to clear cut distinctions and separations.  Variety is a constant in life on Earth and very important to evolution:

These individual differences are highly important for us, as they afford materials for natural selection to accumulate, in the same manner as a man can accumulate in any given direction individual differences in his domesticated productions.  (50)

Darwin goes on to give examples of various species/varieties that are contested, including Rubus, Rosa, Hieracium, and Brachiopods.  He also mentions the primrose and cowslip (Primula veris) and the several varieties of oak trees.  He considers the contested species/varieties to be invaluable:

Those forms which possess in some considerable degree the character of species, but which are so closely similar to some other forms, or are so closely linked to them by intermediate gradations, that naturalists do not like to rank them as distinct species, are in several respects the most important for us. (51)

He refers to highly contested varieties as incipient species.  These varieties have the potential to one day become distinct species.  Here’s another quote from the second chapter, which I think is important, even if it is long:

Hence I look at individual differences, though of small interest to the systematist, as of high importance for us, as being the first step towards such slight varieties as are barely thought worth recording in works on natural history.  And I look at varieties which are in any degree more distinct and permanent, as steps leading to more strongly marked and more permanent varieties; and at these latter, as leading to sub-species, and to species.  The passage from one stage of difference to another and higher stage may be, in some cases, due merely to the long-continued action of different physical conditions in two different regions; but I have not much faith in this view; and I attribute the passage of a variety, from a state in which if differs very slightly from its parent to one in which it differs more, to the action of natural selection in accumulating (as will hereafter be more fully explained) differences of structure in certain definite directions.  Hence I believe a well-marked variety may be justly called an incipient species; but whether this belief be justifiable must be judged of by the general weight of the several facts and views given throughout this work. (55-6)

Darwin spends the rest of the chapter discussing observations he and others have made concerning the patterns found in various genera.  He also makes it a point to mention that not all incipient species will actually make it to the level of distinct species.  Some will retain their current features because it is most beneficial, and some will simply go extinct.

Darwin Day

Happy Darwin Day!

So, I haven’t finished On the Origin of Species.  I’ve only finished the introduction and first chapter.  I know, I’m a lazy lazy monkey.  But the bone chilling cold and non-stop snow this past week give me an excuse.  I kind of hibernated when I wasn’t being blinded by all the shiny light-reflecting snow.  It gave me a headache.  I want spring!  Now!

Ok.  I’ve given my lame excuses and whined a bit.  On to the post.

I’m reading the Penguin Classics version of the book published in 2009 and edited by William Bynum.  It’s a good edition so far.  The intro had lots of neat information. 

Chapter I is titled “Variation under Domestication” and is a nice way of easing readers into Darwin’s findings.  Instead of thwacking his readers over the head with something new and, at the time, potentially shattering, Darwin starts with something many of his readers will be familiar with – Domestic animals and their various forms.  This chapter sets up the rest of the book nicely and gave me lots of great “I’m gonna pause here and look this up” research moments.  For fun I’m including some of these moments and links to relevant information for each:

Esculent:  I had to look this word up.  It’s amazing how many words exist in the English language.  I’ll be learning new ones until the day I die. 

Pigeon Breeding:  Darwin was a pigeon fancier and used the little buggers as examples throughout much of the first chapter, along with other animals and plants.

Doggies:  Darwin brings up dog breeds and his take on their possible ancestry.  I decided to look up information on the evolution of dogs.  This became a family project which involved my Hubby and me taking turns reading information out loud and pondering doggie nature (Cracked.com has a humorous article about this) and human-dog interactions over thousands of years.  The corgi-pup also participated.  Mainly by looking at us like we were crazy and insisting that dogs only became “domesticated” because they felt sorry for humans and thought we’d make nice pets. 

Breed standards:  Darwin mentions breed standards while discussing inheritance and variation.  I have a Bengal Cat and a Pembroke Welsh Corgi, so I decided to do a little more digging on breed standards for these two.

Thoughts on the ancients:  “The pear, though cultivated in classical times, appears, from Pliny’s description, to have been a fruit of very inferior quality.  I have seen great surprise expressed in horticultural works at the wonderful skill of gardeners, in having produced such splendid results from such poor materials; but the art, I cannot doubt, has been simple, and as far as the final result is concerned, has been followed almost unconsciously.  It has consisted in always cultivating the best known variety, sowing its seeds, and when a slightly better variety has chanced to appear, selecting it, and so onwards.  But the gardeners of the classical period, who cultivated the best pear they could procure, never thought what splendid fruit we should eat; though we owe our excellent fruit, in some small degree, to their having naturally chosen and preserved the best varieties they could anywhere find” (42-3).  I never thought about the taste of fruit over the centuries.  Neat!  Another reason living in the present is better than living in the past.  It always bothers me when people paint the past with a utopian brush.  Things have mostly proceeded to get better over the last few thousand years of civilization, not worse.  Even a simple thing like a pear demonstrates this.  Yummy.  Now I want pears.

Final thoughts:  Variation occurs in large enough populations.  This is easily seen in large herds and gardens.  Some variations may be selected for by breeders as being beneficial or better fitting of breed standards or improving breed standards.  These selections can also be made on an unconscious level for various reasons.  Over generations an accumulation of selected variations can create a new breed.  It seems pretty simple when you think about it.

Obligatory Evolution Links:

Wikipedia Entry

PBS

Understanding Evolution

TalkOrigins