On the Origin of Species - Chapter 2

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On the Origin of Species - Chapter 2

Post #1

Post by otseng »

What is Darwin's point in chapter 2?
How well does this support his theory of natural selection?

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Post #2

Post by otseng »

Darwin's point is that from the species level on down, there is evidence of variation among plants and animals. This points to descent with modification in nature.

"These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage."

He mentions several times that it is difficult to define species, sub-species, and varieties. And it is even more difficult to categorize into one of these.

"Nor shall I here discuss the various definitions which have been given of the term species. No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally the term includes the unknown element of a distinct act of creation. The term 'variety' is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved."

(And I'm not sure what he meant by "act of creation" in the above statement.)

He points out that there is no objective measure of how to classify things.

"Hence, in determining whether a form should be ranked as a species or a variety, the opinion of naturalists having sound judgement and wide experience seems the only guide to follow. We must, however, in many cases, decide by a majority of naturalists, for few well-marked and well-known varieties can be named which have not been ranked as species by at least some competent judges."

"From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience sake."

So, there is a gradual transition between species/subspecies/variaties, and it is only logical that these shared common ancestry. On this point I would not disagree with him.

Where he is lacking in this chapter is evidence for a gradual transition for genera and higher. The only thing he mentions is that a large genus will have a large number of varieties.

"it has invariably proved to be the case that a larger proportion of the species on the side of the larger genera present varieties, than on the side of the smaller genera."

Though I'm not sure this is any more than a truism.

In this chapter and the previous, the main evidence he presents is changes in the species level and lower. He is not able to demonstrate any hard evidence of a descent with modification on a higher level. But, we'll wait for further chapters to see if evidence is brought forth.

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Post #3

Post by strevisa »

otseng wrote:
So, there is a gradual transition between species/subspecies/variaties, and it is only logical that these shared common ancestry. On this point I would not disagree with him.

Where he is lacking in this chapter is evidence for a gradual transition for genera and higher. The only thing he mentions is that a large genus will have a large number of varieties.

...

In this chapter and the previous, the main evidence he presents is changes in the species level and lower. He is not able to demonstrate any hard evidence of a descent with modification on a higher level. But, we'll wait for further chapters to see if evidence is brought forth.
Two points.

1. Species may end up looking like each other by chance.
Darwin's stuff is based on macroscopic observable traits.
Thus, a dolphin and a shark may have similar fins, but boy are they different!

2. As far as evidence for modification, Darwin had no clue what a gene was, let alone how they replicate and change.
Moreover, darwin never saw the birth of a species, and never did genetic manipulations.
We can't ask for the impossible: Darwin has no solid explanation for evolution. For a solid explanation we need to wait for experiments around 1940 such as the one with pneumococci inheriting traits shown to be linked to DNA (to the disbelief of the researchers).

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Post #4

Post by Nilloc James »

strevisa wrote:
otseng wrote:
So, there is a gradual transition between species/subspecies/variaties, and it is only logical that these shared common ancestry. On this point I would not disagree with him.

Where he is lacking in this chapter is evidence for a gradual transition for genera and higher. The only thing he mentions is that a large genus will have a large number of varieties.

...

In this chapter and the previous, the main evidence he presents is changes in the species level and lower. He is not able to demonstrate any hard evidence of a descent with modification on a higher level. But, we'll wait for further chapters to see if evidence is brought forth.
Two points.

1. Species may end up looking like each other by chance.
Darwin's stuff is based on macroscopic observable traits.
Thus, a dolphin and a shark may have similar fins, but boy are they different!

2. As far as evidence for modification, Darwin had no clue what a gene was, let alone how they replicate and change.
Moreover, darwin never saw the birth of a species, and never did genetic manipulations.
We can't ask for the impossible: Darwin has no solid explanation for evolution. For a solid explanation we need to wait for experiments around 1940 such as the one with pneumococci inheriting traits shown to be linked to DNA (to the disbelief of the researchers).

Best regards,
Siro
I think he did a decent job of explaining his theory considering he did not have knowlage of genes. Anyways I think it was this thoery that led to latter research.

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Post #5

Post by otseng »

strevisa wrote:Two points.

1. Species may end up looking like each other by chance.
Darwin's stuff is based on macroscopic observable traits.
Thus, a dolphin and a shark may have similar fins, but boy are they different!
Yes, Darwin could only go by morphological features. But, I'm not sure what you mean by species could end up looking like each other. Does Darwin mention anything about this in the chapter?
We can't ask for the impossible: Darwin has no solid explanation for evolution. For a solid explanation we need to wait for experiments around 1940 such as the one with pneumococci inheriting traits shown to be linked to DNA (to the disbelief of the researchers).
I'm not asking for genetic evidence, but simply an extension of his analysis of morphological features.

Here is what I'm noting. Darwin claims that there is evidence of gradual transitioning from species level on down. And I agree with this. But, he does not show that above the species level there is a gradation of morphological features in this chapter. And we'll have to wait to see if he does present any evidence of this or an explanation to account for why we do not see this.

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Post #6

Post by strevisa »

otseng wrote:
strevisa wrote:Two points.

1. Species may end up looking like each other by chance.
Darwin's stuff is based on macroscopic observable traits.
Thus, a dolphin and a shark may have similar fins, but boy are they different!
Yes, Darwin could only go by morphological features. But, I'm not sure what you mean by species could end up looking like each other. Does Darwin mention anything about this in the chapter?


We can't ask for the impossible: Darwin has no solid explanation for evolution. For a solid explanation we need to wait for experiments around 1940 such as the one with pneumococci inheriting traits shown to be linked to DNA (to the disbelief of the researchers).
I'm not asking for genetic evidence, but simply an extension of his analysis of morphological features.

Here is what I'm noting. Darwin claims that there is evidence of gradual transitioning from species level on down. And I agree with this. But, he does not show that above the species level there is a gradation of morphological features in this chapter. And we'll have to wait to see if he does present any evidence of this or an explanation to account for why we do not see this.
1. No, he doesn't.
The reason why I mentioned it was in reference to what I quoted and my relative answer.

2. As far as HIS analysis of morphologies, no doesn't offer more on the topic.
In his favor this should be said, though:
Darwin understood that biosystems change and form an array of specimens (similar to a Gaussian curve one can add).
This is probably the best thing he said, and a fact (the Gaussian distribution) that to this day many people fail to grasp.

His problem is that he equated the array with the "engine" pushing evolution.


As far as OTHER analyses of morphologies: do they - or can they - reveal gradation of morphological features higher than species?
You bet.
One famous example is the formation of the human fetus that goes through non-mammalian phases (e.g. fish-like) before completion.
However, Darwin had no access to such data.

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Siro

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Post #7

Post by otseng »

A general point. As per the guidelines for the book debate, "we are debating the book on its own merits. Usage of modern science to either attack or defend Darwin's points cannot be used." So, I'm not asking how modern science addresses the issues, but rather noting how Darwin addresses the issues in the book.
strevisa wrote:Darwin understood that biosystems change and form an array of specimens (similar to a Gaussian curve one can add).
This is probably the best thing he said, and a fact (the Gaussian distribution) that to this day many people fail to grasp.
Not sure what you mean here. Could you quote what Darwin stated in regards to a Gaussian distribution?

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Post #8

Post by strevisa »

otseng wrote:A general point. As per the guidelines for the book debate, "we are debating the book on its own merits. Usage of modern science to either attack or defend Darwin's points cannot be used." So, I'm not asking how modern science addresses the issues, but rather noting how Darwin addresses the issues in the book.
strevisa wrote:Darwin understood that biosystems change and form an array of specimens (similar to a Gaussian curve one can add).
This is probably the best thing he said, and a fact (the Gaussian distribution) that to this day many people fail to grasp.
Not sure what you mean here. Could you quote what Darwin stated in regards to a Gaussian distribution?
First of all, I understand quite well Darwin is to be evaluated in light of what was available to him.
The reason why I mention later forms of science (and state thy are later) is to dispell possible confusion about Darwin's world.
I do so because most people are not aware of Darwin's world, it was a world where bacteria were hypothetical, and no one knew of viruses (or prions), etc.
Thus, at times it is important to make statements about his world to clarify the point.

Second, as far as Darwin adressing the issue, you yourself quote a statement I made that shows exactly what you were looking for: Darwin understood biosystems generate arrays of specimens.
Most of his argument rests on that.

Finally, as far as Gaussian distribution, those are words I used. I never said Darwin used those words (just double check what I wrote and you quote).
I said that his diversification could be presented as a Gaussian distribution.
Do notice that Gauss and his work were known by the time Darwin wrote his book.

Since you appear interested in passages from Darwin's book that can be constructed to present Gaussian distributions, here is the last paragraph of Chapter 2:

"We have, also, seen that it is the most flourishing and dominant species of the larger genera which on an average vary most; and varieties, as we shall hereafter see, tend to become converted into new and distinct species. The larger genera thus tend to become larger; and throughout nature the forms of life which are now dominant tend to become still more dominant by leaving many modified and dominant descendants. But by steps hereafter to be explained, the larger genera also tend to break up into smaller genera. And thus, the forms of life throughout the universe become divided into groups subordinate to groups."

Last but not least, I am not here to defend or attack Darwin.
I am here to double-check what I know, or think I know, about Darwin before investigating pre-Darwinian theories of evolution.

Best regards,

Siro

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Post #9

Post by Greenbeard »

otseng wrote:...he does not show that above the species level there is a gradation of morphological features in this chapter. And we'll have to wait to see if he does present any evidence of this or an explanation to account for why we do not see this.
I'm not sure what you're getting at. Why should there be any gradual 'transition' between extant species?

Going back to your guidelines for the debate, it might be helpful to realize that the whole macro vs. micro false dichotomy was not only not mentioned by Darwin, it was not implied in his work, not necessary for his ideas to work, and has never been part of a biological program of research. It is a false dichotomy seized upon by detractors of the idea of evolution, most of whom are not biologists. It really has no biological meaning. It is a sort of broad category, but you won't find any programs studying macroevolution - they study paleontology or taxonomy. So, if Darwin didn't mention it (therefore falling outside of your own debate rules) and it plays no part in historical or even modern biology, why bring it up? Why dwell on it? The ideas of Darwin do not sink or swim depending upon the issue of macro vs. micro. When the term 'macroevolution' has been used biologically, it is to describe some of the effects or artifacts of evolution, not a process.

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Post #10

Post by otseng »

Greenbeard wrote:
otseng wrote:...he does not show that above the species level there is a gradation of morphological features in this chapter. And we'll have to wait to see if he does present any evidence of this or an explanation to account for why we do not see this.
I'm not sure what you're getting at. Why should there be any gradual 'transition' between extant species?
What I'm simply trying to point out is that in chapter 2, Darwin presents evidence of species changing, but they do not become a wholly new species. And that we'd have to wait for future chapters to see what evidence he presents that novel species can arise.

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