Absolutely, but in essence that's more speculation than factual data, but one could still make a list of creatures features that could be speculated on as to why it was retained as a beneficial mutation/feature.
Some of it was, yes. I will try to use more citations in this one.
I find the problem with a few of the examples you have listed is that they really do not aid in the creatures ability to survive or reproduce/find a mate etc. For example the eye brow displacing moisture to the side of the face to prevent moisture entering the eye, this would hardly be life threatening, nor enhance its chances of survival, and if it rains the water is going to enter regardless, and in regards to the eye brow and S@xual selection you would need to prove why females (and vice versa) would find eye brows attractive, to me it doesn't appear to enhance someone visually, I could understand where your coming from if peoples eyebrows where rainbow coloured.
Well they serve a function, and evolution isn't all about blatent changes. Even slight advantages in S@xual selection & facial expressions or protection of the eye from liquids/debris/sunlight (or even insects, apparently they provide a more sensitive sense for detecting objects near the eye, like small insects, but I haven't heard of a detailed study of this so I can't be sure. Personally, I think eyebrows can really boost a faces attractiveness, but that's just me.
It also may have been a "carry along". It simply might have randomly came with an individual that had a different mutation that helped in survival situations.
One theory as to why humans lost their fur was because it is apparently better at cooling us down via sweat. Maybe the prevention of sweat/debris from entering our eyes was much more important then if were to run after prey for long distances. But that last part is pure speculation.
Eyebrows also helped in identification and face recognition. Here's
a study about it. It also goes into a bit of detail about the aesthetics and S@xual attractiveness of them.
In regards to the fadeout of the human appendix and the Mexican Tetras eye, this is more of an observed loss of function, I just get a bit confused with the definition,
Here's the one I refer to: "Vestigial characters, if functional, perform relatively simple, minor, or inessential functions using structures that were clearly designed for other complex purposes."
for example it is said the reason that some people are not born with one is because it is not needed (has no function), and because it is vestigial we do not need it (although a recent paper has found the appendix does have a function, and yes I am aware that a vestige can still have a function and that it is the remainder of a past, more important function)
Yes, but as you already clarified, it's not the original function. Maintaining gut flora levels and harboring some bacteria is just a secondary and very minor function. The the specific complexity of the appendix indicates a function that it does not perform.
but if that's the case, what in the body is determining no appendix in the newborns?
Nothing is "determining" it. It's just another mutation. It's so unnecessary that not having one has pretty much no impact upon the human, so the mutation is slowly able to spread without penalty.
We have 2 kidneys, we only need 1, so I could imagine people being born with only one, its also like the dry earwax gene, I understand why we have earwax and why it would be considered a benefit to have it, but the dry earwax gene is so widespread and I don't understand why a non beneficial gene is more widespread than the beneficial one?
Firstly, there are people born with only one kidney. It's called renal agenesis. According to the UK National Kidney Association: "It is not clear why there are normally two kidneys. The human body does not need two kidneys, it could manage perfectly well with one kidney. It may just be that it has been useful for us to develop some parts of the body in pairs (arms and legs), so other parts doubled up as well. It is also possible that there is an evolutionary advantage in having a spare kidney, and this is certainly important in modern medicine, because people can live live normal lives with one normal kidney."
However, after some searching I found a bit more info. Having one kidney can cause:-"High blood pressure. Kidneys help maintain a healthy blood pressure by regulating how much fluid flows through the bloodstream and by making a hormone called renin that works with other hormones to expand or contract blood vessels. Many people who lose or donate a kidney are found to have slightly higher blood pressure after several years.
-Proteinuria. Excessive protein in the urine, a condition known as proteinuria, can be a sign of kidney damage. People are often found to have higher-than-normal levels of protein in their urine after they have lived with one kidney for several years.
-Reduced GFR. The glomerular filtration rate (GFR) shows how efficiently your kidneys are removing wastes from your bloodstream. People have a reduced GFR if they have only one kidney."
They don't seem all that major, however. Maybe (I'm just speculating) that there is a relatively high chances that one kidney will fail, and having a backup is then very useful.
About earwax, well quite frankly I don't know. I looked it up briefly and found this:
"Earwax seems to have the very humble role of being no more than biological flypaper, serving to prevent dust and insects entering the ear. Since it seems unlikely that having wet or dry earwax could have made much difference to an individual's fitness, the earwax gene may have some other, more important function. Dr. Yoshiura and his colleagues suggest the gene would have been favored because of its role in sweating."
However, I still have no idea. Maybe earwax just isn't all that important anymore, since we hygiene and medicine is much more dominant now, and that we no longer have to fight as hard for survival, so previously helpful genes are just becoming less important. That's pure conjecture though!
There are quite a few items in the human body that serve no immediate function but still remain as part of the genetic makeup.
I'm also interested in the "useless behaviors" comment, can you elaborate on this more?
I was referring to vestigial reflexes, eg the goosebumps reflex or newborn babies being able to hold their own body weight when grasping (the way they grab your finger, for instance).
By the way, I apologize for the huge post and all the quote boxes. I got carried away.