This is more of a case of extinction, of failure of a particular "survival strategy", in all likelihood, the squirrels would maintain the genetics to allow them to reproduce brown squirrels.
The point I'm making is more like how there are simple organisms, then over a relatively short period there is the Cambrian explosion... Then theres a period of hundreds of millions of years where there are little changes, then the next era where most of what existed in the Cambrian disappears with a wide variety of species that are mostly all vastly different, with another period of relative evolutionary stability.
So, the point is that while there are periods where there are genetic changes and adaptation, but then there are periods where the environment changes and without a huge change, most species died off...
Ok, well, when we are talking about periods ranging in the hundreds of millions of years, a few hundred thousand year is a relatively brief period.
Which brings up the other issue, being that evolution, with random variations, is not adequate when you are dealing with drastic ecological shifts...
Since we are dealing with geologic timeframes going back hundreds of millions of years, it's difficult to say just how quickly these changes occurred...
In other words, intermediary species appear as shifts in the physical bodies that are significantly different, doesn't quite apply using Darwin's principles... But since, in our lifetimes, we haven't seen any examples beyond truly minor changes, like changes of color, sight, etc..
So, Darwin's theory contains some problems as it stands... If we allow for the concept of a "collective consciousness", then we can explain these issues requiring refinement.
I'm not sure if you're deflecting, or if we're still talking past one another. I'll give you the benefit f the doubt and move on.
The point of the squirrel example is not to debate the evolution of squirrels, but to explain that evolution is not always reactionary process. It is often a function or environmental changes and how they affect an organism. If the change is harmful to the point of potential extinction from the environment causing harm over a short period, then the only way an organism will survive is to have a portion of the population that is already able to cope, or that a portion of the population of that organism lives outside the environment in question. People didn't "adapt" to the plague. The only survivors were either genetically adapted to dealing with it already, or unexposed.
There are cases where the changes in an environment aren't harmful enough to to cause extinction, but the change is so significant that adaptation occurs because it simply provides an advantage. An example might be Flavobacterium that developed a gene for synthesizing nylon (Negoro, S., Biodegradation of nylon oligomers (2000), Appl. Microbiol. Biotechnol. 54, 461-466.). The nylon present in the environment wasn't directly harmful, but may have displaced the bacterium's food source. I said "might be" to describe the adaptations timing because no one knows if the change happened before or after the change to their environment.
To your other point, I'd say that synthesizing a gene to hydrolysing nylon is pretty significant and considering that nylon didn't exist in the environment prior to about 1930 but was discovered just 45 years later is a significant change that happened fast enough for you to see.
In regards to the Cambrian "explosion". I'd be willing to "duel" in sources with you. Mine say that, while the exact length of the Cambrian isn't fully known, the full range of estimates I've seen put it between 10-60 million years with 40 million being the most common, though I admit I have no "hard" evidence for the "most common" 40 million year claim, that's just an anecdotal claim on my part based on my experience.
Some notes I've collected from the web from similar discussions I've had (many with references)....
There are some plausible explanations for why diversification may have been relatively sudden during the Cambrian:
The evolution of active predators in the late Precambrian likely spurred the coevolution of hard parts on other animals. These hard parts fossilize much more easily than the previous soft-bodied animals, leading to many more fossils but not necessarily more animals.
Early complex animals may have been nearly microscopic. Apparent fossil animals smaller than 0.2 mm have been found in the Doushantuo Formation, China, forty to fifty-five million years before the Cambrian (Chen et al. 2004). Much of the early evolution could have simply been too small to see.
The earth was just coming out of a global ice age at the beginning of the Cambrian (Hoffman 1998; Kerr 2000). A "snowball earth" before the Cambrian explosion may have hindered development of complexity or kept populations down so that fossils would be too rare to expect to find today. The more favorable environment after the snowball earth would have opened new niches for life to evolve into.
Hox genes, which control much of an animal's basic body plan, were likely first evolving around that time. Development of these genes might have just then allowed the raw materials for body plans to diversify (Carroll 1997).
Atmospheric oxygen may have increased at the start of the Cambrian (Canfield and Teske 1996; Logan et al. 1995; Thomas 1997).
Planktonic grazers began producing fecal pellets that fell to the bottom of the ocean rapidly, profoundly changing the ocean state, especially its oxygenation (Logan et al. 1995).
Unusual amounts of phosphate were deposited in shallow seas at the start of the Cambrian (Cook and Shergold 1986; Lipps and Signor 1992)
Major radiations of life forms have occurred at other times, too. One of the most extensive diversifications of life occurred in the Ordovician, for example.
Having said that, It sounds to me like you said something akin to, "well there hasn't been much adaptation in the last 500 years (about the time modern science has existed, with 99% of what we've discovered taking place in the last 100 years) so evolution doesn't exist the way the textbooks say.
I'd reply by saying you look MUCH different than you did from when you were 10, but if there was a picture taken of you every day, there wouldn't be a singe picture taken that anyone could look at just one day forward or one day backward that would look significantly different. No single picture that shows that you've changed from a boy to an adolescent to an adult... Does that mean you haven't changed between 10 years old an now?
