Anatomically Correct Angels

Question

As part II of anatomically correct myths here we have the Angel. Angels appear in many cultures and are most commonly seen as simply winged humans. Is there a realistic way that angels could evolve? Using earth or near earth biology how close could I get to the classic Angel? Is there a reason that a Angel couldn't evolve? I imagine that this one will be very hard to justify, so any primate with wings can count as an Angel not just humans.

A list of all of the Anatomically Correct questions can be found here:

http://meta.worldbuilding.stackexchange.com/questions/2797/anatomically-correct-series/2798#2798

Answer 1

If you mean how you can create anatomically correct models of flying humans, then this question can be scientifically and rationally answered. However if you are asking the anatomy of an angel, you are asking an absurd question. You are trying to judge something which is not scientific, under scientific rules. Here I will go on to explain how can you create (in a novel of course) flying humans.

A - Skeletal Structure

You are going to need a very very very light skeleton. That's a prerequisite. We are talking about extremely hollow bones here. At least bird-grade bones or better yet, if you can get pterosaur-grade bones. Pterosaurs were those huge flying monsters that ruled the skies in the times of dinosaurs. Their bones were extremely lightweight. A huge pterosaur (3 times the size of a human) would have bones completely hollow and no more than 1 mm thick. Yeah, now we are talking.

B - Wings

If you examine any flying creature you will find out that their width is greater than their length. That is, you open up their wings, the wingspan will be greater than their length. So a human with 6 ft height would have a wingspan of at least 11 feet when the wings are fully open. Of course the human will fold the wings and keep them on their back just like birds, when not in use.

The next issue is the wing surface area. Are you going to opt for membranous wings (like pterosaurs or bats), crustacean wings (membranous, but different type, ones you see on insects) or feather wings (self explanatory, all bird wings are these types)? I think crustacean wings are not an option as they cannot take high air pressure and would tear open quickly.

Bird feathers are very strong and offer the best air-thrust method, but they are also heavy. Yes! For the scale of human flight, bird feather WOULD be heavy. If you want to use bird feathers for human flight, the shoulder muscles would have to be really really powerful. In case of membranous wings (bat/pterosaur grade), these are relatively light and you can make do with lesser shoulder muscles.

C - Flight Muscle Attachment Points

If you want your flying humans to have wings AND arms separately, then things could get slightly complicated. You are going to have to form muscle attachment points for the wing muscles. These have to have an anchor point on the chest region, like all birds and pterosaurs. So your flying humans are going to have really really stocky and strong chests.

D - Flight Posture

How are your flying humans going to look like, in mid-flight? Are they going to fly in horizontal body posture (like most birds) or vertical posture (the way they stand, looking somewhat like a hovering humming bird)? I cannot answer this myself as it involves a lot of complex aerodynamics, but I think a horizontal flight posture is more likely.

Answer 2

I think the question is could a six-limbed (2 arms, 2 legs, 2 feathered wings) flying humanoid evolve naturally on an Earthlike planet. The answer, I think, is yes*. I don't think the end result would look much like a human though.

Environment

Environmentally, I think that you'd probably be looking at a near earth-sized moon orbiting a gas giant, heated by relatively mild tidal forces. Lots of volcanoes, quakes, new landmasses erupting out of the ocean, tsunamis, etc. etc. I would also expect that gravity is a bit weaker, and the atmosphere a bit thicker with a noticeably higher oxygen content. That would mean you've got a little more room to play with in body size, but they wouldn't be able to fly on Earth.

The key is that I would expect six-limbed life to be common in charismatic megafauna. Basically, I'd expect stuff analogous to centaurs, lammasu, sphinxes, and dragons (not large ones, obviously) to be fairly common on that world. The obvious advantage to flight on this world is that it allows them to escape the disasters much easier, and colonize new land masses very quickly.

Physicality

As I understand it, the main body engineering issue with powered flight is the ratio of surface area to volume/mass to propulsion. To get moving you need propulsion, to stay aloft you need a huge surface area with a narrow profile compared to your volume/mass, but the bigger your surface area, the more mass you have. The more mass you have, the more propulsion you need and the more surface area you need, which costs more mass... and basically the bigger you get, the greater the difficulty in powered flight.

I would expect that each wing is about as long as their body. So if they're about 5 feet tall, I would expect a wingspan of about 10 feet, before any feathers. Feathers would probably add another 2 feet in length on each wing, giving them a functional wing span of 14 feet. I would expect that their manipulating limbs, the ones that look like our arms, to be quite short. I'd guess their fingertips would touch their hip bone. Their resting position for the arms would probably be curled up to their chest, like bird legs. I would also expect that their legs would perform much the same function as a bird's tail, and thus have a rather impressive amount of plumage. Their feet would almost certainly be more like a hawk or an owl's feet, with a larger central "ankle" area and stubbier toes- no talons though. I imagine that they'd stand primarily on their toes. Their face would probably look a lot like a canine's, but with larger eyes, smaller ears, and a much larger brain pan. I'd also imagine that their entire body has some form of feathers covering it.

Biology

They'd need a huge heart, massive wing muscles, hollow bones, and very very efficient lungs, even with the higher oxygen percentage in the atmosphere. They'd fly like vultures or geese, which would help them save energy. They'd need to be primarily carnivorous, to fuel their metabolism, but I could also see them going after seeds and other high-calorie forms of sustenance.

I suspect that you'd see a lot of similar adaptations to birds on earth, with their red blood cells having nuclei and able to see into the ultraviolet. Heck, these 'angels' would either be like birds, and lay eggs, or be like marsupials, and have a stretchy pouch for their partially developed babies. I doubt they'd give birth the way a human does.

If they're tool users, I'd imagine nets to be their primary tool for hunting. In the air, I'd expect lances, bolas, or javelins. They may also have something like a knuckle or a spike on their wings, which would allow them to use their enormous wing strength to defend themselves on the ground.

So basically, you'd end up with something more akin to nightmare fuel than angels if you tried to engineer a biologically successful hexapodal flying creature.

Answer 3

Couple thoughts on this...

1. Angels aren't bred. Meaning, they don't have to mate, have baby angels, evolve, etc. Instead angels are designed and created, like robots, genetically engineered clones, or something, to be servants for God and to perform tasks; be messengers, be protectors, etc.
   This doesn't mean they are unthinking machines, and can still have sentience and will to a point. Sort of a weak AI.
2. Angels aren't confined to 3 dimensions. By existing outside of the 3 dimensions our senses can perceive, angels are able to move unseen, pass through (around, over) physical objects and barriers, and do the other things that angels do, while still being able to interact with our perceived dimension as they need to in order to fulfill duties.
   The best way to picture this is with Flatland. If our world was Flatland, we would see a wall as a barrier that can't be passed through without going through a doorway. But an angel existing in 3 dimensions could "rise above" the flat plain and go "over" the wall. Any angels above the two dimensional plain would be undetectable by any flat instruments since they are unable to look outside of their dimension, but any angel wanting to interact with Flatland would only need to descend or reach down into the plain, or even hover just above it and whisper into your ear (or subconscious).
   The book Spaceland by Rudy Rucker has a lot of similar ideas, where a being living in a fourth dimension interacts with our 3D world.

Answer 4

A biggest problem here is that a classical angel cannot fly with classical angelic wings. They are just too small. A hand glider gives a rough idea what wings are required to have a human airborne. And, obviously, nobody can really flap such wings.

If you are OK with flyless angels, the sexual selection can go long way developing purely decorative appendages.

Answer 5

The first question to ask is how do they get wings in the first place? There are three ways i can think of this occurring from a realistic standpoint.

1) All land animals evolved from a being with 6 limbs, Two of which became wings

2) An evolutionary ancestor had an adaptation which later became wings

3) Wings are technologically grafted onto the creature/added to their DNA and over time adaptations occur which help support them.

Well, 1 is in my opinion the boring solution so i won't cover that, and 3 requires them to be both technologically advanced enough to graph wings (biological or mechanical) and have a valid enough reason to want wings in the first place. So i'll be exploring 2.

Now, for my own ideas i decided to look into the mammalian evoltionary tree. Initially i planned on having a mammalian ancestor gain a neutral mutation (one that doesn't positively or negatively affect their chance of survival) but then i came across Pelycosaurs (early, mammal-like reptiles). More specifically, Sail-Backed Pelycosaurs. and i though to myself 'Now If i just added a second sail, these would be an ideal base to give mammals wings'. So i looked into other animals (most extinct) who had two fin-like or sail-like structures going down their back, and hey presto i found one (i cant remember its name at the moment however). So, having two sail-like wing stuctures are possible in reality.

From here the question becomes Why do they have these structures? and why keep them? Well, when in doubt about creating a certain adaptation or stucture, unless it gives them severe physical issues, have 'Mating Displays' be the reason it exists. A way to showoff that X creature is tougher and more powerful, and therefore able to produce offspring that is more likely to survive.

Ok, we have the How and the Why. Now to decide how they become used for flight and what appearance they will take, Will they be used to showcase how high X can jump? Will they be useful in catching prey? Will X use them to increase the distance they can jump/glide?. What will they look like? Fully fused, Feathered and bird-like? Made of a thin membrane like a bats? a little hairy like a pterosaur? or structured like an insect's wings?

Now other things to consider with this approach: what adaptations do you want them to have? Now, if you want them to be basically like a human, just with wings, then the creature they descend from needs to have been a climber at some point -> This is so dexterous, grasping 'hands' can form, allowing for complex tool use and creation. If they are bipedal, then there likewise needs to be a reason to which bipedalism is necessary and practical. Lots of little things (if you want to get hugely in depth about it) that are mainly covered by the topics above.

Most of this came from my own exploration into the topic of 'humanoid beings with wings' but there are likely other possible answers as well.

Answer 6

As an addition to @Youstay Igo because a comment wouldn't work:

Evolution of an Angel:

One of the few ways I can see an Angel-like creature starting to appear, is in a type of polynesian archipelago with lots of vulcanic features as well as hard to traverse terrain on the islands.

At first the proto-angels that evolve will start using simple tools. If most of the islands lack treewood capable of sustaining good boats, for example because the wood is heavier than water (not sure if possible in that climate), then a large portion would need to swim to colonize other islands and perhaps survive off the fish and sea-fruit they eat there. Recently scientists discovered that mankind is still evolving, with one "species" of human living so exclusively in (shallow) waters that they have trouble walking on land and adapt to the water well with genetic mutations that support their lifestyle. This evolution isn't unheard of, as Dolphins and Whales are thought to have been land mammals that returned to the water. Now take this evolution further: They will retain their arms and hands to keep using the simple tools they have access to, but need to develop easier ways to swim. They won't just evolve flaps between their fingers, but their shoulderblades could create extrusions to form a crude type of fins, which will later evolve to have musculature for easier steering in water and the basics of "flight" under water like Pinguins who "fly" under water. These fins would become the precursor to wings.

As the evolution goes on and more and more of the islands in the area become inhabited, some of these proto-angels will need to start moving inland for food and sustenance. Whether it be predators they try to escape from by climbing trees ASAP or having to scale and jump across dangerous terrain, those fins could start to evolve to support jumping into the tree's and over the terrain, evolving the proto-angels to create a lighter skeleton and more musculature for their proto-wings. Because they are still tool-using creatures and the islands will eventually start evolving wildlife and plantlife that is suitable for intelligent life to start using, intelligence will start becoming a larger part and their arms will also start evolving, without devolving the wings necessary to remain capable across the islands. In fact, the first truly flying angels would be able to scout out islands, settle them and benefit from any foodsources far better than any other proto-angel that came before. The intelligence could also be the defense mechanism to the predators that stalk the thinner and lighter skeleton Angels. This could be the method to Angel evolution.

How would an Angel be build up?

Birds have wings that are attached to the torso with truly massive muscles compared to the rest of the bird. These wings would need to use a kinematic chain similar to humans do when jumping. This kinematic chain would connect the arm musculature to the wings and allow strength from the chest muscles to be passed through to the wings. This would mean that the arms would have a lower movement range to compensate.

Materials wise, the Angel is likely in need of some special stuff. Besides a bird-based lung system and a ridgid chest, it would need some special stuff to keep light and strong. For example, by making all ligaments spidersilk-based you can reduce the amount required and thus the mass, and bones would need to be some carbon-enhanced material such as incorporating Carbon Nanotubes into the normal bones for extra lightweight strength. Spidersilk based products might also be the option for the surface area of the wings, if you like the feather aestetic the feathers themselves could use spidersilk to remain light, thin and still strong.

Answer 7

The average human is 165 cm tall and 62 kg. The angel's bones will be hollow, which should reduce its weight by about 10%, so it will weight 55.8 kg. I am going to be basing the wings off of a golden eagle's. A golden eagle has a wing loading of 7.08 kg/m², in order to get an angel to fly, it would need wings with an area of 7.88 m². Since a golden eagle has a wingspan of 2 m and a wing area of 0.65 m², the angel's wings need to be 12.12 times the surface area and 3.48 times the length, giving a wingspan of 6.96 m, or 22.8 ft. Using the same method with various other birds gives a wingspan of 6.54-12.89 m, a wing area of 6.12-21.26 m², and a wing loading of 2.625-9.12 kg/m². But we're going to stick with our 6.96 m golden eagle angel.

https://www.pnas.org/content/pnas/104/30/12398.full.pdf

Now that we have the size figured out, let's focus on the actual anatomy. In order to fly properly, our angel will need a keel attached to a large barrel-shaped ribcage. It will also need very large, very powerful pectoral muscles. These should be directly attached to the bases of the wings, so the angel will have to be armless (hexapodal vertebrates are not very plausible anyways) the arms having instead been modified into the wings. It would also need very large, very efficient, perhaps bird-like lungs to provide oxygen to its huge flight muscles.

So our angel is a 5'5", 123 lb armless human with a 23 foot wingspan.

Answer 8

Considering that a canonical angel of most religions is not as much a winged human as an energy being capable of manifesting to human witnesses, the issue of their anatomy and physiology becomes a moot point. I would propose that what human eye perceives as wings could be the two overlapping cocoon-like energy fields with a humanoid silhouette in the middle, thus, an illusion of a winged human. As far as evolution of such beings, it's up to the author, since we're talking about creatures evolved far beyond their material body.