You wrote (emphasis mine):
"I said mutations are the result of copying errors. So it seems to me,
the marginal benefits of a mutation, must be so due to other factors."
That's not an answer to my question. What mechanism do you propose produced the ability for these creatures to do this?
That mutations "revert" or have to revert in order to return to a similar form. That's not how mutations work.
What exactly do you mean by "a new arrangement? Can you explain please.
Sure. Let's say the arrangement of the genome for beak shape is:
AAGBCGA
However, due to a copying error, part of the genome is altered:
AAGCGA
So the 'B' has been removed, but this didn't "delete information" as much as it changed the sequence. This change can have a variety of effects, but let's for the sake of simplicity say that B played a vital role in making sure the beak was a particular shape. Now, the beak is a slightly different shape - let's say, long and sharp. However, a further change in a genome:
AAGGA
Removes 'C', and let's say that C played a vital role in making the beak longer and sharper. Now, even if the genome no longer has the 'B' that made sure the beak was flatter and more blunt, the lack of 'C' means it is now free (or more free) to be more blunt and flat once again.
No mutation had to necessarily "revert" in order for this to occur. It's all done progressively. Of course, this is a dramatic, dramatic oversimplification, but if you would like more specifics I'd advise you to ask someone more versed in genetics than me.
Mutation
It is important to distinguish between DNA damage and mutation, the two major types of error in DNA. DNA damage and mutation are fundamentally different. Damage results in physical abnormalities in the DNA, such as single- and double-strand breaks, 8-hydroxydeoxyguanosine residues, and polycyclic aromatic hydrocarbon adducts. DNA damage can be recognized by enzymes, and thus can be correctly repaired if redundant information, such as the undamaged sequence in the complementary DNA strand or in a homologous chromosome, is available for copying. If a cell retains DNA damage, transcription of a gene can be prevented, and thus translation into a protein will also be blocked. Replication may also be blocked or the cell may die.
In contrast to DNA damage, a mutation is a change in the base sequence of the DNA. A mutation cannot be recognized by enzymes once the base change is present in both DNA strands, and thus a mutation cannot be repaired. At the cellular level, mutations can cause alterations in protein function and regulation. Mutations are replicated when the cell replicates. In a population of cells, mutant cells will increase or decrease in frequency according to the effects of the mutation on the ability of the cell to survive and reproduce.
One direction.
Where do you think I've written anything that contradicts this? What do you think this extract is saying?
Why does the mutation occur? You seem to think mutations choose what to do.
They don't. Mutations are random, and they are not driven by conditions - i.e.
because the organism was placed in a situation where the mutation would be useful.
That's not what I've written. Please try to pay more attention. I said a mutation only proliferates IF it produces an advantage. That doesn't mean the mutation wasn't random - it means that, from the random mutations that exist, the ones that DO provide a benefit will multiply.
If you introduce poison, you can indeed drive mutations, but not where you want them to go. Drive them crazy, yes. You can only hope cells survive, to win over the invasion, but it won't be the mutation that drove the adaptation.
No, it will be natural selection. I've already explained that.
This is perhaps due to your presupposing that mutations are responsible for all the changes you see.
Then propose another mechanism that produces variation through reproduction.
I often wonder why people use various lengths of humming birds in the same way, rather than attribute it to different genes of the various "species" mixing.
That could be responsible, but then where would that variety of species have come from in the first place?
You notice we have noses of different sizes and shapes, and other features. You don't think that's due to mutations, do you?
... Yes.
Because it demonstrably and literally is. Variations in humans are due to mutations and differences in DNA.
You kind of lost me with this paragraph though It seems a bit incoherent.
What is incoherent about it? It's very simple:
A mutation which arises that produces an advantage to survival will lead to organisms carrying that mutation having a survival advantage. It really is as simple as that.
I can't figure out how the second population is connected to the first spreading out.
You're unaware that populations can grow too large for one ecosystem to sustain them, or of populations migrating?
Are you saying some remained in the original location, and the second population moved there and mixed?
I'm saying the first population significantly increased in number, leading to a spreading out of the species over a wider area. That's what happens when a relatively small number of animals in one location grows - they have to spread out to find new food sources and/or living spaces.
Demonstrate what please? That the man lied, when he said, "F
or the moths, the dark colouration developed because they were trying to hide, but the butterflies use bright colours to advertise their toxicity to predators."
I'm sure I did.
Mutations are random
...mutations do not "try" to supply what the organism "needs." Factors in the environment may influence the rate of mutation but are not generally thought to influence the direction of mutation. For example, exposure to harmful chemicals may increase the mutation rate, but will not cause more mutations that make the organism resistant to those chemicals. In this respect, mutations are random — whether a particular mutation happens or not is unrelated to how useful that mutation would be.
Whether a particular mutation happens or not is unrelated to how useful that mutation would be.
You seem confused. Do you understand that he doesn't literally mean that the mutation AROSE because of then need for it, but that the mutation PROLIFERATED because it provided an advantage?
Let's say we have a population of shrews that live on the floor of a forest, and these shrews have a brownish fur that allows them some degree of camouflage with the forest floor that protects them from predators. This developed due to natural selection, as the lighter-haired shrews tend to be easier catches for the predators, resulting in the darker-furred shrews being more likely to survive. Over time, the lighter-haired mutation was significantly overtaken by the darker-haired mutation, resulting in future generations of the shrew being almost entirely darker haired.
Now, if I was to say "The darker fur developed because of the shrew's need for camouflage", I am not literally saying "the mutation appeared because the shrew's genome decided it would be really useful to have camouflage". I am saying "this particular mutation proliferated within the population and became the standard because it was environmentally selected for".
Do you understand?
