Chapter IV - Natural Selection
p81) This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.
Hmm, I was once told that nothing can be selected for, only against because basically, if you don't have the right stuff you die.
p82) ...a change in the conditions of life, by specially acting on the reproductive system, causes or increases variability...
Lamarkism, or Darwin just trying to make sense of what he didn't know?
p87) What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species.
Maybe not on purpose, but there must be some examples of co-evolving species that shows modifications of one species being good for another?
p106) Generalists versus specialists!
...forms produced on large areas...will give rise to most new varieties and species.
I know you people discussed this but I would really like to see the data on that because even though it sounds logical, maybe it isn't true.
p107) Do all 'living fossils' come from inhabiting a confined area?
p108) That natural selection will always act with extreme slowness, I fully admit.
Opposite of punctuated equilibrium?
p109) I can see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature's power of selection.
I absolutely love this quote. Is there a limit to the amount of change? I can think of possibly two: 1) organisms will retain their use of DNA; 2) organisms will never be found in a gaseous state. I am iffy on point 1.
The section on extinction gets me excited for some reason :). What IS the maximum amount of species that existed on the earth at one particular time? Min.? How would we ever know? Does the number of species fluctuate with the earth's changing climates and habitats????? Can someone please build me a time machine?
p110) Hence, rare species will be less quickly modified or improved within any given period [compared to common species] and they will consequently be beaten in the race for life by the modified descendants of the commoner species.
This seems like a reasonable assumption for Darwin to make, but how often does this really occur? Maybe sometimes rare species are modified more quickly with changes in habitat.
p119) The modified offspring from the later and more highly improved branches in the lines of descent, will, it is probable, often take the place of, and so destroy, the earlier and less improved branches...
Again, this is always implied but is this really how evolution always works? I know it's hard to get actual data on this but it is really very important. But then Darwin goes on to explain anagenesis, where "the process of modification will be confined to a single line of descent". However, what about multiple lines of descent where the ancestor is not "destroyed". Also on p121, Darwin states "the original parent-species itself, will generally tend to become extinct". Generally, but not always? But then, maybe to hedge his bets, on p122 Darwin states that if "...the modified offspring of a species get into some distinct country, or become quickly adapted to some quite new station, in which [both] do not come into competition, both may continue to exist."
p121) ...the species, which are already extremely different in character, will generally tend to produce the greatest number of modified descendants.
This could easily be tested. Did Darwin already have the data?
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Hi Tonya,
Quick thoughts in response to your comments:
p81) I don't think Darwin's wrong here. What natural selection cares about is relative fitness. If a mutation arises that confers high relative fitness, the bearers of that mutation will increase in frequency relative to those who lack it. Whether you call this selection "for" the mutation or selection "against" those who lack it seems to me to be a matter of semantics.
p 82) I'd say the latter (although he clearly allows a small role for Lamarkism elsewhere).
p 87) Sure, there are plenty of examples where evolution of one species has side effects that are beneficial for others.
p 107) Ceolocanths (perhaps THE classic example of living fossils) are actually quite widely if perhaps patchily distributed in the Indian Ocean. And sharks are sometimes referred to as living fossils, in that the basic shark body plan hasn't changed in 300 million years, even though particular shark species have waxed and waned. Sharks are globally distributed, of course.
p 109) Yes, this is a wonderful quote. And it's right, or at least there's surely no way to falsify it. The only relevant evidence we have is the history of life so far, which managed to get from a prebiotic chemical soup to complex multicellular organisms in a couple of billion years or so. Who's to say that in another few billion years one couldn't have gaseous organisms? Denying this is arguably just a confession of the limits of one's own imagination. And as Francis Crick said, "Evolution is cleverer than you are."
p 110) It has been sometimes argued by followers of Sewell Wright that rare species are prone to undergoing "genetic revolutions" that promote rapid evolution to new adaptive peaks. But the evidence for this is really scanty, whereas we have many lines of evidence that selection is more effective in large populations.
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