Are these “flaws of evolution”?

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There are several facts one wonders why evolution evolved some traits that look disadvantageous. The typical example that comes to mind is the appendix that has no function in our digestive system, and it can easily become infected. But several other aspects can be cited. Wisdom teeth in humans are also an example of a poor construction. They are of poor quality, and there is often not enough room for them in the jaw. Women have a narrow birth canal, which makes a suboptimal solution because childbirth both more dangerous and more painful than in other species.

The human eye is constructed so that the ‘cables’ lie on top of the retina and block some of the incoming light from reaching the photosensitive cells. Not very smart. There are no photosensitive cells in the blind spot, but you are not noticing this partial blindness on a daily basis because the brain compensates for the lack of visual information. Chlorophyll molecule is only able to utilize between 1 and 2 percent of the available energy in the sunlight. Humans are not able to synthesize the all-important vitamin C, unlike other mammals. Therefore, we must either obtain vitamin C through our food or die from scurvy.

Both the food that should be heading for the stomach and the air that should be heading for the lungs, enters our body via the same channel—the pharynx. The air, the food and the water follows the same route down to the point where the pharynx splits into the windpipe (trachea) and the oesophagus. The windpipe is luckily equipped with a small valve or flap—the epiglottis—that stops food from entering it, but the epiglottis sometimes closes too late. The result is that food enters your trachea, where it can cause fatal choking.

How should we interpret that according to modern evolutionary theories? Just flaws of evolution or could these ‘anomalies’ be explained otherwise?
 
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  • #2
phinds
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Are these “flaws of evolution”?
You are improperly applying rationality to evolution. There is none. A "mistake" or "flaw" implies a plan that can go wrong. Evolution isn't like that. Sometimes things are advantageous but become dis-advantageous over millennia.
 
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  • #3
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There are several facts one wonders why evolution evolved some traits that look disadvantageous.
It is not really a 'flaw' of evolution: it is more like a flaw of expectations. Evolution works with many tiny changes, so to 'undo' long established structures is just unlikely to happen. Degradation might occur (like some fishes living in caves 'forgot' to develop eyes) but fundamental changes are not likely.

Also, these tiny changes are not necessarily optimal changes. They are just what comes up and sticks.
 
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  • #4
berkeman
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The typical example that comes to mind is the appendix that has no function in our digestive system, and it can easily become infected.
https://en.wikipedia.org/wiki/Appendix_(anatomy)

Functions
Maintaining gut flora
220px-Appendix_function_diagram.svg.png


A possible function of the human appendix is a "safe house" for beneficial bacteria in the recovery from diarrhea

Although it has been long accepted that the immune tissue surrounding the appendix and elsewhere in the gut—called gut-associated lymphoid tissue—carries out a number of important functions, explanations were lacking for the distinctive shape of the appendix and its apparent lack of specific importance and function as judged by an absence of side effects following its removal.[12] Therefore, the notion that the appendix is only vestigial became widely held.

William Parker, Randy Bollinger, and colleagues at Duke University proposed in 2007 that the appendix serves as a haven for useful bacteria when illness flushes the bacteria from the rest of the intestines.[13][14] This proposition is based on an understanding that emerged by the early 2000s of how the immune system supports the growth of beneficial intestinal bacteria,[15][16] in combination with many well-known features of the appendix, including its architecture, its location just below the normal one-way flow of food and germs in the large intestine, and its association with copious amounts of immune tissue. Research performed at Winthrop–University Hospital showed that individuals without an appendix were four times as likely to have a recurrence of Clostridium difficile colitis.[17] The appendix, therefore, may act as a "safe house" for beneficial bacteria.[13] This reservoir of bacteria could then serve to repopulate the gut flora in the digestive system following a bout of dysentery or cholera or to boost it following a milder gastrointestinal illness.[14]

Immune and lymphatic system
The appendix has been identified as an important component of mammalian mucosal immune function, particularly B cell-mediated immune responses and extrathymically derived T cells. This structure helps in the proper movement and removal of waste matter in the digestive system, contains lymphatic vessels that regulate pathogens, and lastly, might even produce early defences that prevent deadly diseases. Additionally, it is thought that this may provide more immune defences from invading pathogens and getting the lymphatic system's B and T cells to fight the viruses and bacteria that infect that portion of the bowel and training them so that immune responses are targeted and more able to reliably and less dangerously fight off pathogens.[18] In addition, there are different immune cells called innate lymphoid cells that function in the gut in order to help the appendix maintain digestive health.[19][20]
 
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  • #5
BillTre
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How should we interpret that according to modern evolutionary theories?
Many of these examples involve the modifications of previous structures or functions or have functions that are not obvious.
Just flaws of evolution or could these ‘anomalies’ be explained otherwise?
Depends on how you want to define "flaws".
They do not need non-evolutionary explanations.
I will go through some examples:

appendix: has other functions (site of some immune functions as well as a back-up of gut flora (beneficial bacteria)) See @berkeman's post.

wisdom teeth: were probably evolved in the larger jaws of prehumans and got crowded together as the size of the jaw evolved to be smaller. There apparently has not been enough selection against this number of teeth to cause a reduction in the population's "normal". However, there are probably human mutants with fewer teeth.
They are of poor quality, and there is often not enough room for them in the jaw.
Not always true.

narrow birth canal encumbering childbirth: there lots of trade-offs with body dimensions, bodily changes at birth, child head size, etc. This is not the only aspect of birth canal size that is relevant to selection.

eye:
human eye is constructed so that the ‘cables’ lie on top of the retina and block some of the incoming light from reaching the photosensitive cells. Not very smart.
These would be the output axons of the retinal ganglion cells. They are optically clear and have little effect on the incoming light. Interestingly, the independently evolved squid/octopus eye has a very simliar set-up to the vertebrate eye (to which you refer), except that their output axons run under the photoreceptors.

There are no photosensitive cells in the blind spot, but you are not noticing this partial blindness on a daily basis because the brain compensates for the lack of visual information.
This is a functional solution that takes care of any problems that arise out of the output axons needing a pathway out of the eye. It seems to work well, so its not really a problem.
More like an offense against design esthetics (see @phinds above).

Chlorophyll:
Chlorophyll molecule is only able to utilize between 1 and 2 percent of the available energy in the sunlight.
Show me a chemical system that does better.
As a life form it also has to be able to replicate itself to be successful.

Vitamin C:
Humans are not able to synthesize the all-important vitamin C, unlike other mammals. Therefore, we must either obtain vitamin C through our food or die from scurvy.
I am guessing that this trait evolved in a population that did not lack for vitamin C in their diet. So at that time no need for the gene and it gets lost.
Later humans expanded their range and occupied environments to include places where vitamin C was not naturally high in their diets. The gene could not be as easily re-evolved anew as it was to get lost, so either occurying those new spaces become more difficult, or impossible, or behavioral strategies (which humans are good at) are used to overcome the problem (such as taking vitamins or preferentially eating fruits). This could be a compensating behavioral evolution, which only the capacity for thoughty behavior is required to be encoded (such as grow a bigger brain).
Another way to look at this to consider high altitude humans where normal humans would be oxygen limited (lower partial oygen pressure at high altitudes). This limits successful occupation of a particular environment. In some cases, certain human populations have genetics to deal with this (Tibetans and people living in the Andies have genes that better adapt them to high altitudes).

Pharynx:
Both the food that should be heading for the stomach and the air that should be heading for the lungs, enters our body via the same channel—the pharynx. The air, the food and the water follows the same route down to the point where the pharynx splits into the windpipe (trachea) and the oesophagus. The windpipe is luckily equipped with a small valve or flap—the epiglottis—that stops food from entering it, but the epiglottis sometimes closes too late. The result is that food enters your trachea, where it can cause fatal choking.
The food path was there first. Breathing air evolved afterwards.
The pharynx is one of the oldest structures among vertebrates (very basic function of processing food).
This is not a structure that will be easily changed in vertebrates, since it is also involved in a lot of developmental process that depend upon it for their developmental processes to correctly produce other important structures (there is a lot of contingency in developmental processes).

Primitively, O2 and CO2 gas exchange happened through gills or across the skin.
The lungs evolved as bag-like expansions off of the gastrointestinal system (of which the pharynx is an anterior part). The first air breathing fish (not uncommon) gulped down air to go into this bag where O2 could be taken up. Eventually, things got fancier and lungs evolved.
Because development is what generates adult structures, changes in development gradually evolved to generate a more complex structure.
You are kind of stuck with the issues that go with it, but they are dealt with through various workarounds.

Evolution doesn't make a long term plan and build toward that.
It goes little step by little step.
Each step having to be overall adaptive for the organism (considering all of the different effects it might have), finally reaching the point we are at now, which can at first glance look non-optimized.
 
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  • #6
PeterDonis
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How should we interpret that according to modern evolutionary theories? Just flaws of evolution or could these ‘anomalies’ be explained otherwise?
These are not "anomalies". They are exactly what you should expect from an evolutionary process that has no foresight and no intelligence involved, but is simply natural selection applied to random genetic variation under conditions of changing selective environments.
 
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  • #7
Janus
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Not always true.
I, for example, still have all my wisdom teeth, and have no issues with crowding.
 
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  • #8
atyy
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There are several facts one wonders why evolution evolved some traits that look disadvantageous.
Evolution simply means that living organisms are descended with change from previous living organisms. The fundamental laws governing evolution are the laws of physics and chemistry, not the idea that evolution maximizes adaptive advantage.

Some outcomes of evolution may be described as advantageous (eg. increase the ability to survive) for the animal, and natural selection is the theory of how evolution produces these results.

However, it is important to note that natural selection is less fundamental than evolution. One could think of natural selection as only one of several mechanisms of evolution. Sexual selection is an example of a mechanism of evolution that is different from natural selection, as it may lead to traits that are disadvantageous in terms of the animal's survival.
https://www.nature.com/scitable/knowledge/library/sexual-selection-13255240/
https://www.pnas.org/content/106/Supplement_1/10001
https://academic.oup.com/beheco/article/26/2/533/258654

Other mechanisms of evolution:
https://www.nature.com/scitable/kno...lection-genetic-drift-and-gene-flow-15186648/
https://www.nature.com/scitable/topicpage/neutral-theory-the-null-hypothesis-of-molecular-839/

Some sites use terminology in which sexual selection is a type of natural selection - terminology that I do not prefer - but the idea is the same - there may be different types of "selection" that "maximize" different and opposing types of "advantage".
 
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  • #9
256bits
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Many of these examples involve the modifications of previous structures or functions or have functions that are not obvious.
Backwards compatibility perhaps could describe it from a systems approach.
 
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Backwards compatibility perhaps could describe it from a systems approach.
Well, that's not really a good description. It works more like a scrapheap challenge. What is useful will be kept but still might be modified: everything else is just raw material for repurposing or got tossed around.

But it is unlikely to get some bars of construction steel starting form a wrecked car, for example.
 
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  • #11
256bits
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Well, that's not really a good description. It works more like a scrapheap challenge. What is useful will be kept but still might be modified: everything else is just raw material for repurposing or got tossed around.

But it is unlikely to get some bars of construction steel starting form a wrecked car, for example.
Ok. I'll take the note.
I don't really want to be an instigator of a description that is less than a good analogy.
 
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I think "flaws of evolution" needs to be better defined to have an intelligent conversation about it.
 
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Also, the human backbone is a pain. Where did that come from? I think of that every time I see one of those fish bumper stickers. Not intelligent design.
 
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BillTre
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Also, the human backbone is a pain. Where did that come from?
A defining vertebrate trait.
Found in all vertebrates. Was present in the last common ancestor of all vertebrates, an early fish or sub-fish (lamprey/hagfish).

Not intelligent design.
Unguided, non-intelligent design.
 
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the human backbone is a pain. Where did that come from?
Notochords from some ancestor vaguely lancelet-like. :smile:
 
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  • #17
phinds
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Also, the human backbone is a pain.
Well, have yours removed if you don't like it.
 
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  • #18
BillTre
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Notochords from some ancestor vaguely lancelet-like. :smile:
Interestingly (to me any way), the notochord pre-patterns the vertebrae (backbones) along the body axis.
It also triggers the development of the CNS floorplate (ventral midline of the CNS), adjacent longitudenal blood vessels, and different parts of the somites (mesodermal segments that in part become vertebrae).
(I found a zebrafish mutant in which the notochord does not develop (the floating head mutant (fih)).)
 
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  • #19
pinball1970
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There are several facts one wonders why evolution evolved some traits that look disadvantageous. The typical example that comes to mind is the appendix that has no function in our digestive system, and it can easily become infected. But several other aspects can be cited. Wisdom teeth in humans are also an example of a poor construction. They are of poor quality, and there is often not enough room for them in the jaw. Women have a narrow birth canal, which makes a suboptimal solution because childbirth both more dangerous and more painful than in other species.

The human eye is constructed so that the ‘cables’ lie on top of the retina and block some of the incoming light from reaching the photosensitive cells. Not very smart. There are no photosensitive cells in the blind spot, but you are not noticing this partial blindness on a daily basis because the brain compensates for the lack of visual information. Chlorophyll molecule is only able to utilize between 1 and 2 percent of the available energy in the sunlight. Humans are not able to synthesize the all-important vitamin C, unlike other mammals. Therefore, we must either obtain vitamin C through our food or die from scurvy.

Both the food that should be heading for the stomach and the air that should be heading for the lungs, enters our body via the same channel—the pharynx. The air, the food and the water follows the same route down to the point where the pharynx splits into the windpipe (trachea) and the oesophagus. The windpipe is luckily equipped with a small valve or flap—the epiglottis—that stops food from entering it, but the epiglottis sometimes closes too late. The result is that food enters your trachea, where it can cause fatal choking.

How should we interpret that according to modern evolutionary theories? Just flaws of evolution or could these ‘anomalies’ be explained otherwise?
You are looking at a single point in time rather than looking at ancient features and seeing where they ended up.
 
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  • #20
Evo
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Evolution is just changes, good or bad, the bad are discarded or left unused or can cause damage, there are no "flaws of evolution" because evolution isn't perfect, it doesn't head in a specific forward positive direction, and if you think it does, you need to go back and study what evolution is.
 
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