How do fit parents prevent their offspring from being fit?
They have no say in the matter. Which particular sperm and which particular egg come together to form a fertilized egg, and whether there where any mutations incorporated in the particular sperm or egg, or whether mutation errors occur during subsequent development of the egg is all random chance. Whether the resultant offspring is sufficiently adequate to survive long enough to reproduce would remain to be seen and is also determined by other factors not related to fitness but to chance circumstances. If lightning starts a forest fire and the animal gets trapped and dies in the fire, that was simply bad luck in the face of a transient circumstance.
Do niches evolve so fast that birds and rabbits are whipsawed by the environment that makes being faster, stronger, or smarter useless?
I wouldn't use the term evolve, rather, I would say ecosystems change. How fast or slow that change occurs is not fixed. Some environments or ecosystems may stay relatively unchanged for millennia or eons. Take oceans depths for example.
Rate of change is a relative thing and dependent on the specific factors at hand, with some changes easily adapted too despite a fast change, while even a slow change can spell doom for a species that has no way to get from their current configuration to one that will survive the changes to come. Here I think of those animals suited to an ice age environment that could not adapt to its recession.
There is always the chance for catastrophic change, such as a large meteor strike, such that nothing survives within a certain range of ground zero and the rest may or may not be sufficient to weather the immediate global change that results. Whatever is left simply has to keep plugging along and will either be sufficient to the task of survival and reproduction, or won't.
If survival of the fittest is a random walk then why do species change? How does a random walk lead to speciation?
The change in sexually reproducing organisms is constant. I am not genetically identical nor physically identical to my parents, nor they to theirs, etc. Second, it is not about fittest, but being adequate or sufficient. If an offspring's set of characteristics are insufficient for current conditions, they die. Could they have been sufficient for some other condition, location, time, or circumstance? Certainly. The randomness of environment and circumstances is what chooses winners and losers, i.e. who makes it long enough to reproduce or not.
Isn't every individual pretty much stuck with the genes from his parent?
For now, yes, and certainly in the wild. With the advent of gene therapies however, this will probably change. Oh, also creating designer genomes is also a possibility in the future.
How does an individual adapt?
Once born some organisms have mechanisms to adapt to changes or transient circumstances. Many organisms can regulate their metabolism within certain ranges, allowing them to handle both cold and warm environments. Obviously, use and disuse of muscles leads to strengthening or atrophy of muscle groups, such that dominant activities can better condition the organism to that activity. Take running or swimming for example. For humans, getting better at running by running does not necessarily translate to getting better at swimming, or vice versa. Organisms with memory systems can potentially learn and remember circumstances that pose a threat and adapt their behavior accordingly.
Yes! Exactly. Every individual is equally fit.
No, every individual is different to some degree. Whether they are sufficiently adequate to survive to reproduce will be tested by their circumstances.
Mutation is irrelevant to the discussion because it is the chief means by which species change outside of bottlenecks. This has been stipulated and is irrelevant to the belief in survival of the fittest.
Hmmm. Hardly irrelevant to acknowledge an active contributor to why organisms continually change each generation. What is significant with mutation is the possibility for dramatic changes, which can equally doom the offspring, be a neutral consequence, or enhance its survivability in current conditions. Additionally, if neutral under current conditions, when passed down may be advantageous to subsequent generations that receive it given their particular conditions, or doom them. Only time will tell.
This is the point here and it is illogical.
All genes breed true. All individuals are similar to their parents. Therefore each generation is by definition more fit than the previous if Darwin were right. If species change through survival of the fittest then there is a continuing improvement in every species until they change one by one. It is irrelevant that this is not a straight line process, it would still exist if survival of the fittest drove speciation.
All genes breed true? How do you explain birth defects? Please, take a second to think things through.
Genetic variation among organisms is constant as a result of sexual reproduction and mutations. Genetic change occurs regardless. Speciation is the result of their being a wide variety of ecosystems for Life to exploit. Time, environment, and circumstance determine which characteristics that arise in a constantly changing genome are sufficient for survival, and with Life exploiting different conditions, different species arise with their specific dominant characteristics sufficient to survive in some portion of those different conditions.
