We are all made of stars. When you think about the universe and life at its most basic level we are all made up of atoms and other tiny particles. A tree is made up of similar atoms as is a sink and a shoe. So what separates us from a shoe? The answer is obvious we are alive but there are many tiny microorganisms that are alive that are still not counted as animals – so what makes an animal? There are certain scientific rules that an organism or lifeform must have to be considered an animal.
Movement
The first required capability is movement or mobility. While all animals move at different speeds and in different ways, they all move. Kangaroos jump, horse gallop, cats stalk, birds fly, fish swim but they all are capable of moving. You may at this point be thinking back to something like coral which is considered a living object and in some circles defined as an animal, but even coral moved when it was larvae. Plants and fungi are not required to move (although some do) – animals must.
Reproduce
The majority of animals engage in some form of sexual reproduction. While only a small percentage of animals engage in sex for pleasure, nearly all engage in sex of some kind, for procreation. This is where two lifeforms combine their genetic information in any way to produce a third lifeform. Some animals do reproduce on their own, asexually. Some plants and fungi do reproduce as well so it is not exclusive but it is found in some shape or form in all animals.
Multicellularity
When it comes down to it there are many living organisms that we don’t consider animals. Most of these are amoeba. By definition an animal must be multicellular – i.e. have more than one cell. Although the number of cells can vary, it must be great than one. The ringworm always has 1,031 cells, the human always has trillions. Again some plants are multicellular. You may be starting to wonder what makes us so different from plants.
Advanced nervous system
The key difference between plants and animals as well as animals and everything else is the level of sophistication of our evolution. While some plants eat, sleep, and have sex, none talk, or wink. Only mammals are advanced to have developed sight, sound, hearing, taste, and touch. Some animals have even more sense like echolocation or magnetic understanding. At the basis of these senses is an incredibly complex nervous system. This is what separates advanced animals from the rest of the natural world. Of course, some technical animals lack these senses but they will still have a more developed nervous system than plants or fungi.
Food ingestion
All living things need energy to live. This comes in the form of carbon and it allows living things to grow and survive. There are two known ways to get carbon. The first is from the environment – by breathing carbon dioxide – gas in the atmosphere. The second is by eating other carbon-rich organisms. If something that is alive gets carbon from the environment it is called an autotroph. If it gets it by eating other living organisms it is called a heterotroph. Animals are heterotrophs. Some plants, fungi, and even bacteria are also part heterotroph so it is not exclusive but it is a requirement of animals.
When it gets down to a basic level it is clear that there is not that much that separates the animal world from the plant world. If you ever see a plant walking around or winking at you then it has likely broken a rule of science and the world no longer makes sense, or it is just a very good Halloween costume.
