Genuine Puzzles In Biology?

Probably has a lot to do with being a bilaterally symmetrical animal. I would hazard a guess that modern diets differ greatly from the our ancestors' diets. Those diets may have contained a lot of toxins that needed to be filtered out. The liver also stores glycogen which would have been important for hunter/gatherers that experienced a feast-famine type of lifestyle.

Yes and no. The circulatory system is very bilateral, and the kidneys can best be described as being part of that system. Inside the peritoneum bilateralism breaks down quite a bit.

Actually, it's not. Hair is a good insulator. For many species who take it easy during the heat of the day it acts like a ice cooler, keeping the relatively cooler body insulated from the relatively hotter air.Humans do not take it easy during the hottest time of the day. We evolved to hunt during these periods. How can we do this? Evaporative cooling. We sweat. When water evaporates off of our skin it takes heat away from the body. Most animals use a similar technique by panting, but this is only capable of using the small surface areas. In humans, we use the entire surface of our skin.So how does this give us an advantage? We can actually run down animals until they collapse from heat exhaustion while we remain relatively unaffected. Some human tribes still use this technique to this day. Was the scalp/hair warmer or cooler than the rest of the body?Also, using a treadmill effectively eliminates evaporative cooling compared to someone running down the road.

IMO, pattern recognition is hard wired into the most primitive portions of our brain. This is why trout do not have to learn to recognize the shadows of flies as they rest on the surface of a stream. Their brains already know what patterns are food and which are not.The same for humans. We have patterns associated with danger hard wired into the most primitive portions of our brains. This may be why we call them irrational fears because it overrides the grey matter that evolved in more intelligent species like us.

Me too. I was raking up leaves one time and somehow spun a wheel on an upturned skateboard. It was one of the old style with the bb's for bearings that make this rasping sound. The rustling sound made by the spinning wheel and the bb's rattling around in the wheel sent me into immediate panic mode. My heart rate went from 70 to 200 within seconds. After I calmed down a bit I laughed my ass off, but there was no laughing for about 5 seconds.

I did say that earlier in the thread. The difference between the modern skateboard bearings and the older bearings is that there is a gap between the bearings in the older models which allows them to rattle around.But to get back to pattern recognition, I think it is a holistic thing. I remember quite vividly the moment I put the rattling and the rustling together. What popped in my head was the picture of a snake, immediately followed by intense panic. And yes, it made me feel like an absolute fool. I think it is a matter of having just enough information to trigger the response.

If these phobias are ingrained deep in our evolutionary history, then yes it is very possible. Many of the mammals that made it through the K/T extinction event were small, burrowing, nocturnal mammals which are the very description of a snake's favorite prey.Edited by Taq, : No reason given.

You seem to have confused your terms. Epigenetics refers to DNA methylation and histone packaging. Genetic comparisons use the actual DNA sequence, as does genetic drift.Perhaps you meant to refer to DNA regulation as a function of DNA sequence instead of epigenetics?

So what we are really looking at is the complexity of the DNA regulatory network.If we are going to relate this to DNA sequence divergence then we need a good idea of how many bases are involved in this network and the specific bases in those DNA sequences that are under selection. There could also be spacing issues between regulatory sequences and the genes they are regulating, so indels have to be considered as well.I think even the most modest estimates would find that the majority of bases are selectively neutral, so genetic drift would still be the cause of the majority of differences.

However, coding DNA makes up a tiny portion of the whole genome, somewhere around 3%. In this model, the other 97% of the genome is diverging through drift so the predominant force of genetic change is still drift.

Selection is hard to put into the calculations so population geneticists try to use selectively neutral DNA seqeunces that can be readily identified (especially for genomic position to rule out duplication events). One good source for these sequences is pseudogenes, which is exactly what this group used:A molecular approach to estimating the human deleterious mutation rate - PubMed