vossler said:
So since it appears all humans are of the same classification, at least when it comes to evolution, we're all undergoing some sort of transition together. No one is being left behind right?
All living humans are the same species of human (
Homo sapiens sapiens). But your question seems to assume that you see evolution as a transformation of each individual simultaneously. At least that is what "no one is being left behind" suggests to me.
In evolution, it is not individual humans (or rabbits or parrots, etc.) which transform. It is the
species which transforms. Individuals differ from one another. That is what makes for variation in the species.
Evolution occurs when the pattern of variation changes from one generation to the next. And when that pattern of variation continues to change in a specific direction over many generations, the younger generation may be distinctly different from its ancestors.
Now each individual contributes his or her own variation to the pattern for his or her own generation. But s/he does not change her own variation. A person born with blue eyes, blood type A, curly hair will not change over their lifetime to a person with black eyes, blood type O and straight hair. So what is key is not the characteristics of the individual, but how many other individuals in the species share the same characteristics.
In Generation A, what % of the population has blue rather than black eyes? What % have blood type A rather than blood type O? what % have curly rather than straight hair?
Now the people in Generation A reproduce and pass their characteristics on to their children. If all of them are equally sucessful in reproducing, these percentages will be the same in Generation B. (This comes from Mendelian genetics.) But what if they are not all equally successful in reproducing? What if Generation A people with blue eyes have, on average, more surviving children than Generation A people with black eyes? Then in Generation B, the % of blue-eyed people will be larger than it was in Generation A. Same for the other characteristics. In Generation C the percentages change again, and in Generation D, yet again.
Now let us carry this over a thousand generations. Let us suppose that in the first generation 90% of the people have blue eyes, blood type O and straight hair. And in the 1000th generation 90% have black eyes, blood type A and curly hair. That kind of change is evolution.
Now lets also suppose that each of the three new characteristics spreads through the population at a different rate. Suppose that it takes only 300 generations to change the dominant eye colour from blue to black, but 600 generations to change the dominant blood type from O to A and 900 generations to change the dominant hair type from straight to curly.
Now what would a typical transitional form be?
In generation 500 we would expect almost everyone to have blue eyes, somewhat more people with A rather than O type blood, and a lot of people whose hair is somewhere between straight and curly. In other words a mixture of new vs. old traits and/or traits intermediate between the new and the old.
The transformation is not in specific individuals, but in the overall pattern of variation in the species. But specific individuals each stand somewhere in the spectrum between the old dominant pattern and the new dominant pattern. Each will have either all the characteristics of the old dominant pattern, or all the characteristics of the new dominant pattern or a mixture of old and new. Those in the last group are transitional.
But it is not they themselves that are transforming. It is the species that is transforming.
On a still larger scale we can see the same sort of transformation making the differences between species and higher taxa.