An animal (from Latin anima "breath, soul; a current of air"; replaced "beast" in 1600s from Latin bestia "beast, wild animal") is a multicellular, eukaryotic organism.

Animals, along with plants, make up fauna_. However, animals are distinguished from plants_ in that they cannot make their own food. The bodies of animals are made up of cells organized into tissues, each specialized to perform a specific function.


1   Substance


For every type of animal there is a most convenient size, and a large change in size inevitably carries with it a change of form. [1]

Consider a giant man ten times as tall as an average man, but ten times as wide and ten times as thick, so that his total weight was a thousand times average, or about eighty to ninety tons. The cross sections of his bones would be only a hundred times those of an average man, so that every square inch of giant bone had to support ten times the weight borne by a square inch of human bone. As the human thigh-bone breaks under about ten times the human weight, a giant would break its thighs every time it took a step. [1]

Suppose that a gazelle, a graceful little creature with long thin legs, is to become large, it will break its bones unless it does one of two things. It may make its legs short and thick, like the rhinoceros, so that every pound of weight has still about the same area of bone to support it. Or it can compress its body and stretch out its legs obliquely to gain stability, like the giraffe. (I mention these two beasts because they happen to belong to the same order as the gazelle, and both are quite successful mechanically, being remarkably fast runners.)

Gravity presents practically no dangers to the mouse and any smaller animal. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is soft. A rat is killed, a man is broken, a horse splashes. Resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth.

An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble. It can go in for elegant and fantastic forms of support like that of the daddy-longlegs.

Surface tension is as formidable to an insect as gravitation to a mammal. A man coming out of a bath carries with him a film of water of about one-fiftieth of an inch in thickness. This weighs roughly a pound. A wet mouse has to carry about its own weight of water. A wet fly has to lift many times its own weight

Tall land animals have other difficulties. They have to pump their blood to greater heights than a man, and, therefore, require a larger blood pressure and tougher blood-vessels

A typical small animal, say a microscopic worm or rotifer, has a smooth skin through which all the oxygen it requires can soak in, a straight gut with sufficient surface to absorb its food, and a single kidney. Increase its dimensions tenfold in every direction, and its weight is increased a thousand times, so that if it is to use its muscles as efficiently as its miniature counterpart, it will need a thousand times as much food and oxygen per day and will excrete a thousand times as much of waste products. Now if its shape is unaltered its surface will be increased only a hundredfold, and ten times as much oxygen must enter per minute through each square millimetre of skin, ten times as much food through each square millimetre of intestine. When a limit is reached to their absorptive powers their surface has to be increased by some special device. For example, a part of the skin may be drawn out into tufts to make gills or pushed in to make lungs, thus increasing the oxygen-absorbing surface in proportion to the animal’s bulk. A man, for example, has a hundred square yards of lung. Similarly, the gut, instead of being smooth and straight, becomes coiled and develops a velvety surface. The simplest plants, such as the green algae growing in stagnant water or on the bark of trees, are mere round cells. The higher plants increase their surface by putting out leaves and roots. Comparative anatomy is largely the story of the struggle to increase surface in proportion to volume.

Exactly the same difficulties attach to flying. It is an elementary principle of aeronautics that the minimum speed needed to keep an aeroplane of a given shape in the air varies as the square root of its length. If its linear dimensions are increased four times, it must fly twice as fast. So the larger aeroplane, which weighs sixty-four times as much as the smaller, needs one hundred and twenty-eight times its horsepower to keep up. Applying the same principle to the birds, we find that the limit to their size is soon reached. An angel whose muscles developed no more power weight for weight than those of an eagle or a pigeon would require a breast projecting for about four feet to house the muscles engaged in working its wings, while to economize in weight, its legs would have to be reduced to mere stilts. Actually a large bird such as an eagle or kite does not keep in the air mainly by moving its wings. It is generally to be seen soaring, that is to say balanced on a rising column of air. And even soaring becomes more and more difficult with increasing size. Were this not the case eagles might be as large as tigers and as formidable to man as hostile aeroplanes.

The advantages of size. One of the most obvious is that it enables one to keep warm. All warmblooded animals at rest lose the same amount of heat from a unit area of skin, for which purpose they need a food-supply proportional to their surface and not to their weight. Five thousand mice weigh as much as a man. Their combined surface and food or oxygen consumption are about seventeen times a man’s. In fact a mouse eats about one quarter its own weight of food every day, which is mainly used in keeping it warm. For the same reason small animals cannot live in cold countries. In the arctic regions there are no reptiles or amphibians, and no small mammals. The smallest mammal in Spitzbergen is the fox. The small birds fly away in winter, while the insects die, though their eggs can survive six months or more of frost. The most successful mammals are bears, seals, and walruses.

Similarly, the eye is a rather inefficient organ until it reaches a large size. The back of the human eye on which an image of the outside world is thrown, and which corresponds to the film of a camera, is composed of a mosaic of “rods and cones” whose diameter is little more than a length of an average light wave. Each eye has about a half a million, and for two objects to be distinguishable their images must fall on separate rods or cones. It is obvious that with fewer but larger rods and cones we should see less distinctly. If they were twice as broad two points would have to be twice as far apart before we could distinguish them at a given distance. But if their size were diminished and their number increased we should see no better. For it is impossible to form a definite image smaller than a wave-length of light. Hence a mouse’s eye is not a small-scale model of a human eye. Its rods and cones are not much smaller than ours, and therefore there are far fewer of them. A mouse could not distinguish one human face from another six feet away. In order that they should be of any use at all the eyes of small animals have to be much larger in proportion to their bodies than our own. Large animals on the other hand only require relatively small eyes, and those of the whale and elephant are little larger than our own. For rather more recondite reasons the same general principle holds true of the brain. If we compare the brain-weights of a set of very similar animals such as the cat, cheetah, leopard, and tiger, we find that as we quadruple the body-weight the brain-weight is only doubled. The larger animal with proportionately larger bones can economize on brain, eyes, and certain other organs.

The height to which an animal can jump is more nearly independent of its size than proportional to it. A flea can jump about two feet, a man about five. To jump a given height, if we neglect the resistance of air, requires an expenditure of energy proportional to the jumper’s weight. But if the jumping muscles form a constant fraction of the animal’s body, the energy developed per ounce of muscle is independent of the size, provided it can be developed quickly enough in the small animal. As a matter of fact an insect’s muscles, although they can contract more quickly than our own, appear to be less efficient; as otherwise a flea or grasshopper could rise six feet into the air.

1.1   Body weight

In a healthy human adult male, mass is distributed as follows:

Bone ?
Muscle ?
Water ?
Fat ?
Blood 7%
Skin 10-11 pounds (6% of 150lb)

2   Properties

3   Classification

3.1   Mammal


A mammal is ...

3.2   Fish

A fish is an animal that ...

Sharks are INCREDIBLY efficient swimmers, their cartilage skeleton acts like a rubber band, the muscles pull the tail one way and the "bones" whiplash back trying to return to its normal shape. That extra energy is enough to take the tail to the other side of its body where, at that point it just has to pull its tail a bit further and restart the rubber band motion. It's almost a perpetual motion machine just using tiny amounts of energy to pull the tail in place to get the next swing ready!

Sharks are older than trees

3.3   Diet

A herbivore is a animal that exclusively eats plants_.

A carnivore is an animal that exclusively eat the meat of other animals.

An omnivore is an animal that eats both plants_ and meat.

The diet of animals affects the shape of their teeth.

4   Hunting

Hunts like this are usually to cull an older alpha male, who is unable to produce offspring anymore. The alpha has a harem of the best mates, but can't produce offspring. The next in line cannot take over and populations decrease. If we cull these older males, younger, more virile males can take their place and help increase population.

5   Domestication

Dog are very different mentally from cats, especially modern domesticated dogs. We domesticated dogs(by literally beating them into submission for 80K years and only breeding the cooperative ones), cats domesticated themselves so we would feed them(or more likely they were lured in by the rats around our camps that ate scraps and then just decided they liked the easy access to food and stuck around and people started collecting the kittens and killing the extremely unruly ones).

It's dangerous no matter how well adapted to humans they are, because at their core, they're still wild animals. Dogs are almost an entirely unique case. The species would not exist if not for humans. Think about how different wolves are from dogs just physically. Every change in appearence is accompanied by at least one significant change in disposition. Being teachable and loyal is literally part of their genetics.

6   Consumption

Most animal cruelty videos typically depict acting in ways they are not supposed to and misrepresent that what they show is the only way something occurs.

Pigs are slaughter by herding a group into a room, knocking them out with a gas, and then using a bolt to deliver the killing blow while they're unconscious. Pig gassing is the most common method for pig slaughter. Some gassing uses C02 while will trigger feelings of suffocation and intense panic; other non-toxic gases like argon could equally deprive a pig of oxygen without eliciting a panic response.

7   Treatment

People seem to empathize with animals in some hierarchy based on their size, facial display, sound. Possibly complexity of the nervous system. Society says its okay to treat animals in the lower rungs badly.

So far as being an animal is better than being nothing, killing animals is wrong. And that depends on a nervous system.

8   Study

Carl Linnaeus (? - 1778), the "father of modern taxonomy", formalized the modern system of naming organisms.

9   References

[1](1, 2) J. B. S. Haldane. 1928. On Being the Right Size.

Today, most large animals on the planet are afraid of projectiles – an adaption to only one species of predator.

This is why whales are the largest thing to have ever lived iirc, even dinosaurs had a size limit due to their weight becoming a problem, bones can only be so strong and large.

People react to touching a hot surface physically before they consciously are aware.

NOt sure if these are true, but these are beliefs I hold

All animals naturally form a dominance hierarchy.

Animals of the same species may use different mating strategies. This may be based on their position in the dominance hierarchy.