Question on Origin

[lightburst]

Sorry if this was the wrong section. I figured it didn't fit in the Biology section(Or any book forum). Plus it's specifically about a book... so yea... :<

 

So I started reading Origin of Species just for the lulz and at the second paragraph of the first chapter (Variation under Domestication) Darwin talks about how variability happens right before conception than anything else, that is that it doesn't happen during embryo development but rather at that point it was already determined, and says that his reason to believe so was how animals are generally impaired to reproduce when in confinement, sometimes without regard to the level of confinement, and goes on some examples that animals really are impaired to reproduce under confinement.

 

I was sort of with him when he said "But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception." since that made sense to me. He lost me though when he said that this conclusion of his was chiefly based from the "... remarkable effect which confinement or cultivation has on the functions of the reproductive systems..."

 

Now my concern is how did he arrive at that conclusion that variation does not happen on or after conception with the idea that animals cannot reproduce in confinement. Unless I completely read that wrong, I can't follow his reasoning.

 

 

It has been disputed at what period of time the causes of variability, whatever they may be, generally act; whether during the early or late period of development of the embryo, or at the instant of conception. Geoffroy St Hilaire's experiments show that unnatural treatment of the embryo causes monstrosities; and monstrosities cannot be separated by any clear line of distinction from mere variations. But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception. Several reasons make me believe in this; but the chief one is the remarkable effect which confinement or cultivation has on the functions of the reproductive system; this system appearing to be far more susceptible than any other part of the organization, to the action of any change in the conditions of life. Nothing is more easy than to tame an animal, and few things more difficult than to get it to breed freely under confinement, even in the many cases when the male and female unite. How many animals there are which will not breed, though living long under not very close confinement in their native country! This is generally attributed to vitiated instincts; but how many cultivated plants display the utmost vigour, and yet rarely or never seed! In some few such cases it has been found out that very trifling changes, such as a little more or less water at some particular period of growth, will determine whether or not the plant sets a seed. I cannot here enter on the copious details which I have collected on this curious subject; but to show how singular the laws are which determine the reproduction of animals under confinement, I may just mention that carnivorous animals, even from the tropics, breed in this country pretty freely under confinement, with the exception of the plantigrades or bear family; whereas, carnivorous birds, with the rarest exceptions, hardly ever lay fertile eggs. Many exotic plants have pollen utterly worthless, in the same exact condition as in the most sterile hybrids. When, on the one hand, we see domesticated animals and plants, though often weak and sickly, yet breeding quite freely under confinement; and when, on the other hand, we see individuals, though taken young from a state of nature, perfectly tamed, long-lived, and healthy (of which I could give numerous instances), yet having their reproductive system so seriously affected by unperceived causes as to fail in acting, we need not be surprised at this system, when it does act under confinement, acting not quite regularly, and producing offspring not perfectly like their parents or variable.

 

Edited September 7, 2011 by lightburst

[Ophiolite]

Could you confirm the chapter and paragraph you are reading this in. Also which edition. I cannot find the material in the location you specified.

 

Also, some of your grammatical structures are difficult to interpret. For example, what do you mean by " ...how variability happens right before conception than anything else." Or, " animals really are impaired to reproduce under confinement." Did you mean "animals really are impaired in their ability to reproduce in confinement."?

 

Thanks.

[lightburst]

I'm using the first edition, according to the publisher at least. It's literally the second paragraph on mine. It starts off as "It has been disputed at what period of life the causes of variability, whatever they may be, generally act;..."

 

Also sorry for the grammar. I have horrendous formal english. Not to mention it's not my first language. Not that I'll do better in my first language though. lol

 

by " ...how variability happens right before conception than anything else." I meant how variability isn't determined during embryo development or the moment of conception but rather it is determined right before that.

 

"animals really are impaired in their ability to reproduce in confinement."? Yes.

[Ringer]

IIRC there were experiments done to see if Lamarck's theory of inheritance of acquired traits before the publishing of Origin. This was done by cutting off the tails of mice over many generations to see if there was any measurable difference in tail length as there should be if the traits acquired in life are passed on. The tails did not drastically shrink in any way. I assume that is the sort of thing he is talking about if I remember the timeline correctly.

[lightburst]

That part was discussing variation rather than inheritance.

[imatfaal]

That part was discussing variation rather than inheritance.

But that's the point. What Ringer was saying is that there were prior theories that said that variation (in the breed not the individual) could occur during the during the life of the individual. we now know that our genotype is fixed at conception and that environmental variables are only accounted for when a random variation provides a competitive breeding advantage

[lightburst]

But I am asking in the context of Origin. How Darwin got to that conclusion through the idea that confined animals fail to reproduce. How he got there might be false(I don't know) but I'll get there. :<

 

I quoted the whole paragraph I found online if it helps. Its at the first post.

Edited September 7, 2011 by lightburst

[Ringer]

What Darwin is saying is that there is dispute over the time when variation will affect the progeny of any animal. You have to realize in the time that this was written Mendel was all but ignored. So without a grasp on genes role on inheritance they believed that the traits of the parents mixed like paints instead of inheriting sets of chromosomes. Believing this made it difficult to believe variation was inherited because they would just revert back to an average. So the idea of variation happening within somethings life-time became an idea because it would allow the mixing inheritance but would also keep traits because animals in a similar environment would acquire similar traits within a population and changing the average of a given trait. Since the mouse experiment ruled this out it was thought that perhaps the trait was acquired in utero by some means (I can't remember the details of that one). Each had their own problems until the chromosomal theory of inheritance was accepted as being the most likely way animals inherited variation.

 

Darwin got to his idea due to the fact that it is difficult to force animals to breed the way you wish them to. This idea made him believe that there was some sort of mate selection, instead of animals mating randomly, that may be a factor in animals survival. This would change the average traits even with these other elements of inheritance, even though they brought other problems with his theory until genetic variation was discovered. You have to look at what they knew then to really see the genius it took for him to think this up. They knew nothing of what chromosomes did or genetics.

[lightburst]

I can see that but only vaguely though... But sure it does work when I warp it around... It would've been more convenient if he was more explicit. Thanks.

 

Yes I am considering the context of the book, the time when genetics was not yet an accepted/known mechanism.

[Ringer]

It wasn't just not accepted, for all intents and purposes it was unknown. He probably wasn't more explicit because he really couldn't be and he wasn't writing for an everyday audience. The only people who read then were most likely rich and educated, and the only people who read about science were scientists. At the time biology was just a bunch of loosely tied fields that couldn't be brought together. Not to mention the age of the Earth was a heated topic, due to heating problems and geological discoveries, so he was unsure if the timeframe needed for his theory to work was even plausible.

[Laurens]

Yes I am considering the context of the book, the time when genetics was not yet an accepted/known mechanism.

 

You might enjoy this documentary:

http://www.youtube.com/watch?v=MuNFZTQGXCs