How much is too much evolution?

A common mantra among YECs is to say they believe in evolution, but only limited, "horizontal" evolution "within kinds" and not "vertical" large-scale evolution between or above "kinds."  But the problem with such statements is that they are entirely subjective.  I have yet to see a YEC provide a clear answer on this.  What exactly constitutes a "kind"?  How much evolution is too much?  Where exactly do YECs draw the line between acceptable and unacceptable evolution and on what rigorous, scientific basis do they do so?  YECs will often cite the polar extremes but fail to rigorously define where exactly the dividing line is between possible and impossible evolution.  Instead, from what I can tell, YECs base their beliefs on subjective feelings of what seems or "feels" like too much evolution.

For example, these two skulls have similarities but also distinct differences.  Are the differences too much for YECs to acknowledge that they are related?  Comparative anatomy and genetics both support the conclusion that these two are in fact closely related, but YECs will still reject the evidence if they subjectively feel like the differences are too great.

Similarly, comparative anatomy (including sophisticated computer measurements and analysis) and genetics supports the conclusion that all these skulls are related.  

YECs often dismiss such things out of hand (despite the evidence) saying that such changes in morphology are too great, but they have no objective basis for doing so and instead dismiss arbitrarily and based on subjective "gut" feelings of what seems like too much change.

So how much is too much?  Are the skulls above, for example, too different in their range of size and morphologies to be related through common ancestry?

Looking at two things that show similarities only show similarities, they don't show why they are similar only that they are. Jumping to conclusions about historical causes just because of looks isn't a strong argument, it isn't even an argument really. We can see similar things today with common species that have similar traits yet are vastly different. 

No one "jumps to conclusions...just because of looks."  You are trivializing sophisticated analysis.  Detailed quantitative comparisons are fundamental to many scientific disciplines.  For example, we use comparative genetics to determine relationships all the time.  You have no problem with this and even accept the findings of science that two individuals are related if the anatomical or genetic differences aren't "too much" in your subjective opinion, but if you feel like the differences are "too much" then you dismiss it like you've done here.  In other words, you *don't* reject the use of anatomical and genetic similarities to deduce relationships just so long as the differences aren't "too much," but if the differences are subjectively "too great" in your opinion, then suddenly the same method based on degree of similarity suddenly becomes invalid.  But on what basis do you make this determination?  How much is too much?  Where is the dividing line between possible and impossible evolution and how do you know?  

Plus, as I said with the skull examples, it's not simply anatomical similarities but also genetic similarities that support the conclusion of common ancestry.

These skulls have similar morphologies and are also genetically similar (except for one chromosome which is markedly different).  Using the same accepted methods we use in forensic analysis of bones and DNA, we come to the conclusion that these two individuals are related and had a common ancestor:

Anatomical and genetic evidence likewise supports the conclusion that all these skulls below are related and they all had a common ancestor:

See, what you are doing is accepting the use of anatomic and genetic similarities to determine relationships in one case, while rejecting it in another based only on your subjective feelings of what "seems" like "too much" evolution or too great a difference in morphology.

One thing to think about is how closely related species can be. A horse is closely related to a donkey. So closely related that they can inter breed and make mules.

Right and there are noticeable differences in their skeletons particularly in size, but without knowing they are skeletons of donkeys and horses and mules YECs could reject them and say they are not related if the skeletal differences are "too much" in their subjective opinion, which again raises the question I pose to YECs: How much is too much evolution?  Where do YECs draw the line between possible and impossible evolution and on what basis do they do so?

If you quantify change in any way and a change of magnitude X is considered possible, just choose N bigger than Y/X and you know how a change of magnitude Y can be achieved.

If you think they all come from a common ancestor you can arrive at that conclusion readily and if you think a common ancestor for all life is bogus, not so much.

You still haven't answered the fundamental question: How much is too much evolution?  Where *specifically* do you draw the line and on what basis?   

I can see small changes within each lifeform, but not major overhauls.

Can you delineate more specifically where the dividing line is?  Genesis "kind" does not seem to equate with what biologists define as a "species."  Does a Genesis "kind" equate with genus or some other taxonomic category (or somewhere in between?

@TruthMuse

How can you deem something impossible if you don't know what is necessary to get from A to B?

Take the two sets of skulls below.  The first two skulls are related and share a common ancestor.  All the skulls in the second picture are also all related to each other and have a common ancestor.

In both cases, the skulls show large differences in morphology, and I know the underlying genetics in both cases.  In fact, only a few small changes in DNA are needed to create these large changes in skull size, shape and form.  Now if you come along and look at these cases and subjectively it feels or seems like too much change in morphology to suit your taste, then you will tell me it's impossible.  But how can you do so if you don't know how much change in DNA is needed and by what mechanism?   Doesn't that just amount to guessing on your part? 

Depending on how fast the changes in evolution occur, if very slow it would not be in the fossil record I'm be looking for similarities, but in living creatures. There should be strings of very similar life that show the changes that have been occurring over time, instead we see distinct living creatures.

Continuous gradational changes in morphology is the exception rather than the rule not just in the fossil record but in living populations too due to functional and developmental constraints.  Most major discontinuities are.due to small scale changes and tinkering in regulatory genes, gene expression and developmental timing.

If evolution were true, if everything changes slowly, even form. We do not see that in life.

It's a misconception that evolution only occurs slowly via gradual, incremental steps as explained above in post #13

Really, it happens in giant leaps of massive change all at once?

But isn't it the case that evolution takes many generations to manifest itself in the creation of new species and forms? That being the case, we need to study lifeforms with rapid reproductive cycles in order to see evolution taking place and that generally means microbial life.

At least no examples of higher-order lifeforms come to mind that can reproduce on a scale of days. Some rodent species can produce two litters per year but even then would evolved traits be easily identifiable?

But you need to study lifeforms with rapid reproductive cycles and that usually means microbial ones, which are invisible to us. Most of the living things you see in your environment have evolved but often over many generations, involving periods of at least thousands of years or longer.

It depends on what you mean by 'giant leaps of massive change'.  In fact, that is the problem addressed in this thread: YECs rarely define the line between acceptable and unacceptable evolution that represents too great of a change.  The divding line is fuzzy and given no formal, rigorous treatment by YECs, who speak subjectively on the subject.

So I don't know what you mean by 'giant leaps of massive change', and you have yet to clearly, and rigorously locate the divding line between evolutionary change you consider acceptable and unacceptable, so I can only speak in similar generalities.

In general, changes in morphology that you would probably consider 'major' are usually not the result of evolving entire suites of brand new genes, but instead are usually the result of small scale genetic tinkering with what's already available.

Take the vertebrate tetrapod limb, for example.  The various different types and skeletal arrangements (which represent 'major' changes in morphology) can be produced by mere changes in the kinetics (i.e., the rates) of developmental pathways.  

Similarly, all the different, various types of eyes in the animal kingdom and the major differences between them result from tinkering with a single regulatory gene.

Generation time (GT) certainly has an important effect on evolution.  GT is strongly correlated with rates of molecular evolution.  The higher the GT, generally the higher rate of molecular evolution that is observed.

However, that doesn't necessarily mean that it takes many generations for evolution to 'manifest' itself.  First, there are many, many different species that look very similar morphologically.  There are thousands of different species of frogs, for example, that all look like...well, frogs.  So it is a common misconception that speciation is always associated with large changes in morphology.  It usually is not.  Speciation simply requires reproductive isolation/barriers.  Speciation also does not require numerous generations, and can happen instantaneously.

So the question of evolution manifesting different 'forms' is somewhat different from speciation which may or may not be accompanied by significant changes in form. But many generations are not necessarily required for noticeable changes in form to occur either.  Significant changes in form can also occur 'instantaneously'.

One of the complicating factors in all this is the discovery that molecular evolution and morphological evolution occur at different rates and are not as directly correlated with each other as we would intuitively expect.  This, in fact, is why we can study the evolution of specific genes and proteins independently of morphological evolution.  Genetic changes often occur with little to no noticeable effect on morphology.  But the general truth still holds that 'major' changes in morphology are usually not correlated with the evolution of entire new suites of genes, but genetic tinkering with what already exists.

I should also add that evolutionary studies are not restricted to studying natural populations evolving over many generations.  Rather, today actual evolutionary history is 'read'/inferred directly from genomes.