Odd evolutionary outcomes: green fur, body fat, anything else?

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Summary:

limits to evolutionary characteristics
I was watching a grey squirrel the other day who stood out amongst green leaves, and wondered whether there was a reason no mammals have evolved green fur (AFAIK?)? I'm aware there are a couple who allow green algae to grow in their fur (sloth and polar bears).

I mean we have weird things like a mammal with a beak that lays eggs, venomous fangs and detects things with electricity. Green fur would seem positively 'normal'!?

On the subject of evolutionary 'stuff' that doesn't quite make sense, the other one I have pondered on is why we store fat if our calorific intake exceeds our calorific use? I mean , why fat? Why not store it as muscle that would be a bit more useful? Why do we have to exercise to grow bigger muscles, why not store energy in bigger muscles. OK, so fat helps as a thermal insulation, but one only needs so-much thermal insulation? I'd have thought survival would have been better amongst animals that make more muscle than fat (assuming the muscle was evolved to be broken up for energy as a food store if necessary)?

Any other evolutionary odd outcomes with similar unclear reasons?
 

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  • #3
Drakkith
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On the subject of evolutionary 'stuff' that doesn't quite make sense, the other one I have pondered on is why we store fat if our calorific intake exceeds our calorific use? I mean , why fat? Why not store it as muscle that would be a bit more useful?
Fat is very, very easy to break down into sugar (glucose), which cells use to generate ATP for energy. Muscle cells are complex and require many different enzymes to break down, as they are composed of fats, proteins, and other types of molecules. Plus, muscle cells grow in size by increasing the number of myofibrils, a complicated process not particularly well suited to store energy.

I'd have thought survival would have been better amongst animals that make more muscle than fat (assuming the muscle was evolved to be broken up for energy as a food store if necessary)?
Muscle is only broken down for food when the body is out of fat reserves and is the sign that a person or animal is beginning to starve.
 
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  • #4
epenguin
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Good question.
There is also the African green monkey, but in the photos I've seen you practically have to be told its green before you see the slight tinge.

About the fats, a part answer could be these contain almost only carbon and hydrogen so are a bit better Energy source than muscle protein which contains more oxygen and nitrogen. The nitrogen is so to speak hard earned, and so a waste to use it as energy store although it is of course also that (the protein gets hydrolysed and then deaminated to form organic acids which can be oxidised). Because it is hydrophobic fat is also more compact. Throwing fat on the fire gives you some indication of its energy content! By the way as well as an energy store fat is also a water store – i.e. it is oxidised to water as well as carbon dioxide.Water is also a problem to get and conserve for many mammals – humans are a bit exceptional. The camels hump is fat, not water.
 
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phinds
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Good question.
But with a trivially simple answer that the OP apparently didn't even try to find. It would have no evolutionary advantage, so why would anyone expect it?
 
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  • #6
epenguin
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You can suppose green could be an advantage for some predators or prey. Most military camouflage has green in it.
 
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  • #7
jim mcnamara
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Evolution has context - namely the environment it evolved in. So to answer the "green problem", which is your perceived issue -- consider From National Geographic article on sloths:
The sloth is the world's slowest mammal, so sedentary that algae grows on its furry coat. The algae gives it a green tint ....
And - extremely important - you cannot assume logic, direction, or intention to evolution, which is what you are doing.
 
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  • #8
Vanadium 50
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You can suppose green could be an advantage for some predators or prey
Would a kelly green deer be really harder to see than an ordinary one?
 
  • #9
BillTre
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Although the examples provided have their problems, as shown in the responses, the overall issue in the thread title:
Summary:: limits to evolutionary characteristics
is (to me anyway) interesting.

There are limits to what evolution can produce (in the limited time span nature has provided.
Many limitations (disregarding what actual selective forces are available) involve the genetic state of an organism prior to the step to achieve its postulated final state.
Many macroscopic traits involve intricate coordination of many molecular/cellular/genetic components that are not obvious at first glance, like enzyme pathways, embryonic origins, and biophysical properties.

For example, if organism A lacks a whole series of enzymes required to make a green pigment, it would be very unlikely it would suddenly evolve such an ability in any of its immediate descendants. (Such is probably the case with mammalian green pigmentation).

Some (human sought) features not found in organisms seem to be limited by strictly mechanical limitations: non-microscopic rotating wheels use for locomotion are not found because: a efficient vascular system to supply their cells with nutrients, O2, and waste removal has not been evolved. Thus such a structure could not be retained.

Important considerations in these kinds of questions are:
  • Each evolutionary step along the way should have some adaptive value
  • Smaller evolutionary steps are much more likely to occur (they need a precursor state from which the next one can be easily generated). Some are so unlikely as to not be reasonably expected by normal mutational processes.
  • Other, more easily achievable evolved states, that provide the same adaptive benefit will most likely evolve first, removing an adaptive advantage for evolution of a different evolved state
  • Evolution, moving forward, operates more on building upon what what a current state enables (or makes feasible), rather than just on jumping to a final optimal state.
These can be thought of as steps in construction (through evolution) of something useful.
A way to visualize the adaptive aspects of this is as an adaptive landscape:
Screen Shot 2020-09-27 at 9.09.56 AM.png

The red path (starting from the dots) leads to a local peak through small continuously adaptive steps, while the blue path goes through increasingly less adaptive steps before being able to go uphill to the global adaptive maximum.
 
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  • #10
phinds
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Most military camouflage has green in it.
Yes, because PEOPLE can see green. Animal predators can't. Again, no evolutionary advantage. Did you look at the link I posted?
 
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  • #11
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Most military camouflage has green in it.
Is that really true? Much of what I have seen, even for woodland, is gray, tan and brown. (I will not speak of the US Navy's former "aquaflage" fiasco)
 
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  • #12
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I had a brief scan and did not think those answers covered it.

I mean, whether or not green fur is readily seen by other animals rather misses the question why animals have not evolved to see green?

I did not mention camouflage specifically, though that was the lead in of course, but if there was one species that evolved green fur and green sight then they'd be able to see each other better whilst others could not. This might then have reproductive or team-hunting-activity benefits?

Maybe, even, this is why polar bears take on green fur? Easier to see a green bear in the arctic than a white bear if you are looking for a mate?

Hence, if you will forgive me for not jumping immediately to believing everything I read on a single google search, I did not think that google necessarily offered the perfect answers on its first hit (if it ever does?). Thought there might be some intelligent discussion here about it?
 
  • #13
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Fat is very, very easy to break down into sugar (glucose), which cells use to generate ATP for energy. Muscle cells are complex and require many different enzymes to break down, as they are composed of fats, proteins, and other types of molecules. Plus, muscle cells grow in size by increasing the number of myofibrils, a complicated process not particularly well suited to store energy.



Muscle is only broken down for food when the body is out of fat reserves and is the sign that a person or animal is beginning to starve.
Thanks, but you might have missed slightly wider points.

First, it's clear that its much easier to break down fat, but there has to be a point where there is no evolutionary advantage to taking on more fat.

I mean, let me ask a slightly different question; how has evolution taken us to a point where people's bodies can build up so much fat that they are disabled by it?

So one might assume that 'good evolution' would get us to a point where we take on as much fat as is life-benefiting, then we use any further excess for other stuff, like muscle. Doesn't really matter if it is easy to break down or not, just build up more of it if the food is so readily available.

Or in another angle, why do we need to exercise to build up bigger muscles? Why doesn't the body just grow bigger muscles, seems like they might be useful?

Secondly, the idea that muscles are difficult to break down is sticking with the idea that these are the best muscles to have. What I was actually hinting towards was that why haven't we evolved muscle tissue that is as easy to break down as fat, then it'd be a lot more use!! Maybe that is not possible, and we can't tell because there is only one muscle tissue in the animal kingdom so we have no point of comparison?
 
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phinds
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Hence, if you will forgive me for not jumping immediately to believing everything I read on a single google search ...
Fair enough, but playing the game of "why didn't evolution do THIS instead of THAT" seems to me to be a pointless exercise. There are bound to be many dozens of attributes that you could apply this to (if not hundreds). Natural selection just passes on whatever genes give a species the best short term ability to survive and procreate.
 
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  • #15
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Fair enough, but playing the game of "why didn't evolution do THIS instead of THAT" seems to me to be a pointless exercise. There are bound to be many dozens of attributes that you could apply this to (if not hundreds). Natural selection just passes on whatever genes give a species the best short term ability to survive and procreate.
Yes, it's true, there is nothing 'perfected' in the process of evolution so yes I have to agree with you.

I guess it is a 'game' at that level. Just piqued my curiosity, is all; maybe there was some particular reason that is understood fur cannot be green or muscles cannot be easily re-absorbed?

...... collectively, we appear to be an imperfect set of species on this planet! ;)
 
  • #16
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Your scenario shows a favoritism of one strategy - but the reality is there are millions of strategies and they are interlocked in a bigger picture. For example, if predators got too good at hunting, they would hunt their prey out of existence and starve themselves. If prey gets too good at hiding, they could overpopulate, wipe out their own food sources, and kill off their own population. So there has to be a balance between predator and prey for both populations to be maintained healthily. And of course this is just one dimension of survival (starvation/food resourcing). The scenario gets even more complex when you look at other factors (disease, accidental death, birth rates, etc.)
 
  • #17
BillTre
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maybe there was some particular reason that is understood fur cannot be green or muscles cannot be easily re-absorbed?
Fat is the most efficient biological energy storage material by weight.
As mentioned before it is easily made and converted into biologically usable energy.
Withdrawing energy from muscle would result in their functional degradation, which would often be non-adaptive.
Protein is expensive to make, something like 4 or 5 ATP per amino acid residue, not counting the production of the amino acid. I am not sure all of that energy is recovered and biologically useful.

The amount of muscle is determined by both the amount initially grown and physiological processes that make muscles larger with use. This adapts the amount of muscle to what is actually needed in the normal events of the animal's life. Too much muscle will cost in the energy expense of its production as well as its maintenace and in some way hinder other functions. It is not uncommon for body builders to have very large muscles but much more limited movement of their joints. Genetic engineering can increase the amount of standing muscle amounts (in mice, and I believe a natural human mutation). Because this is not a widespread mutation, shows that it is most likely not adaptive for the majority of people.

WRT pigment: I think the only pigment synthetic pathway in mammals (other than photo pigments) is for reds/browns and maybe yellows. Making others would probably require several new enzymes, which might be best acquired by horizontal gene transfer which is not available in mammals until recently with the advent of genetic engineering.
Maybe you want to get on with that.
 
  • #18
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I mean, let me ask a slightly different question; how has evolution taken us to a point where people's bodies can build up so much fat that they are disabled by it?
Too much food is a pretty recent development for humans, and evolution hasn't had time to solve the problems it creates. It's also a problem that affects only a small percentage of the human population, which minimizes any evolutionary advantages that the necessary adaptations would have. We're pretty much stuck with the genes that let bears lard it on. (I hope somebody's researching how bears -and whales- regulate their LDL and HDL and avoid clogged arteries.)

As far as green fur is concerned, plenty of animals (insects, spiders, amphibians, lizards) have protective green coloration, so there's certainly an advantage to it if you live among green plants. The genes for green pigments do exist in humans (green eyes, e.g.), and presumably are lurking, unexpressed, in many our mammalian cousins, so green fur is not an impossibility. It just hasn't happened yet, or if it has, it didn't provide enough of an advantage to spread through the population. (A major change in appearance might also present obstacles to finding a mate ... there aren't many Captain Kirks among the other mammals.)
 
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Secondly, the idea that muscles are difficult to break down is sticking with the idea that these are the best muscles to have. What I was actually hinting towards was that why haven't we evolved muscle tissue that is as easy to break down as fat, then it'd be a lot more use!! Maybe that is not possible, and we can't tell because there is only one muscle tissue in the animal kingdom so we have no point of comparison?
This is a matter of chemisty: the most efficient materials for storing energy are carbon and hydrocarbons (hence the fossil fuel economy) – at least in any biology based on sunlight and CO2 fixation. It's hard to imagine how evolution could ever produce a competitive organism that doesn't store energy as a hydrocarbon of some sort.
 
  • #20
Vanadium 50
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. The genes for green pigments do exist in humans (green eyes, e.g.),
Green eyes aren't green because of green pigment. They are blue eyes (which aren't due to blue pigment either - it's the Tyndall effect) with just a little brown pigment.
 
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  • #21
jim mcnamara
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@Vanadium 50 is completely correct. Plus @BillTre is correct in that most mammals have dichromatic vision, so "green" is not commonly perceived. Canids, Felids, and Mustelids, which have many mammal predatory species, are in this group, and have good night vision, bad color vision.

https://en.wikipedia.org/wiki/Dichromacy

Birds are tetrachromats and can see more colors, including a bit of UV, and all with much greater visual acuity than we humans have. They see
nuances of color that humans cannot see. [ per link below]
Being a green snack item would not help the species evade bird predators any better than other colors.

The "green camoflage" is a largely anthropomorphic point of view, IMO. In spite of the National Geographic link above.

https://www.thespruce.com/how-birds-see-color-386467
 
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  • #22
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Too much food is a pretty recent development for humans, and evolution hasn't had time to solve the problems it creates.
It seems we're too clever for ourselves. We learned to extract sugar from nature so we can consume it and get the dopamine hit that represents nutrient richness without the nutrients. Intelligence has been a risky adaptation.
 
  • #23
BillTre
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It seems we're too clever for ourselves. We learned to extract sugar from nature so we can consume it and get the dopamine hit that represents nutrient richness without the nutrients. Intelligence has been a risky adaptation.
Its the slow learning of evolution (a reward system to seek out nutrients in the former world of scare resources) being over taken by the quick learning of the recently increased human mental capabilities over fulfilling those needs.
 
  • #24
phinds
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Its the slow learning of evolution (a reward system to seek out nutrients in the former world of scare resources) being over taken by the quick learning of the recently increased human mental capabilities over fulfilling those needs.
I think it's more a matter of opportunity. There are things that are readily available and affordable to the average person today that were rarely readily available and rarely affordable throughout most of history.

That is, it's not that we WANT them more but that can have them more easily.
 
  • #25
BillTre
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I think it's more a matter of opportunity. There are things that are readily available and affordable to the average person today that were rarely readily available and rarely affordable throughout most of history.

That is, it's not that we WANT them more but that can have them more easily.
Could be both.
 

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