What is Animals: Definition and 155 Discussions

Animals (also called Metazoa) are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.
Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes, arthropods, and molluscs—and the deuterostomes, containing both the echinoderms as well as the chordates, the latter containing the vertebrates. Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago.
Historically, Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous for Animalia) and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa.
Humans make use of many other animal species, such as for food (including meat, milk, and eggs), for materials (such as leather and wool), as pets, and as working animals including for transport. Dogs have been used in hunting, as have birds of prey, while many terrestrial and aquatic animals were hunted for sports. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion.

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  1. Frabjous

    Here be monsters (Orcas sinking boats on purpose)

    Apparently orcas are learning killer ways. https://www.livescience.com/animals/orcas/orcas-have-sunk-3-boats-in-europe-and-appear-to-be-teaching-others-to-do-the-same-but-why
  2. S

    News What animals are thinking and feeling, and....

    I am not sure exactly which subforum this should be put into, and not sure what title to give this topic, but this video is interesting, called What animals are thinking and feeling and why should it matter. The video's link: .. .. Okay, some time passage, and I watched several more...
  3. Astronuc

    Current disease events in wildlife and domestic animals

    My wife read an article last night about an outbreak of hemorrhagic fever in rabbits, and it has been passing through populations throughout the US. So, I decided to look into it and came across a wildlifehealth.org. There is a lot of nasty stuff out there. Detection of High Pathogenic Avian...
  4. S

    B Sievert lethal radiation doses for Non-Humans (other animals)

    Does every species get its own 5.5%-calibrated sievert? It's morbid to ask, I know, but given that Chernobyl is full of dogs I have to ask whether there is such a thing as a dog-sievert?
  5. Jarvis323

    Can SARS-CoV-2 Successfully Cross Species to Infect Deer Populations?

    We've known that Sars-Cov-2 can be transmitted from humans to a wide range of animals. Now we are learning that it has widely spread through deer populations. https://gizmodo.com/uh-oh-the-coronavirus-has-been-spreading-widely-in-u-s-1847999600 Have we ever observed this kind of thing...
  6. T

    Evolution and preservation of endangered animals

    Recently I saw a video from a Christian creationist who was trying to debunk evolution with an argument that if evolution gives us new species all the time why would we make an effort to preserve those that are going extinct. So I was thinking a little bit about it and these are my conclusions...
  7. Astronuc

    Billion-year-old fossil, a missing link in the evolution of animals?

    https://phys.org/news/2021-04-billion-year-old-fossil-reveals-link-evolution.html I used to have some literature on ancient single cell organisms, but I haven't seen it in decades. https://www.cell.com/current-biology/fulltext/S0960-9822(21)00424-3 Sediments of the Torridonian sequence of...
  8. mark!

    How are parasites able to imitate other animals?

    The green-banded broodsac, a parasitic flatworm, is said to parasitise the eye stalks of snails, and through imitating a caterpillar attracts the attention of a bird. But how does it know what a caterpillar looks like, if it doesn’t even possesses complex eyes? Flatworms have primitive eyespots...
  9. Z

    Animals Beyond Visible Light & Infrared

    Do any animals see in a spectrum other than visible light and infrared?
  10. T

    First ancestor of Humans and Animals

    https://www.cnn.com/2020/03/23/world/animal-ancestor-ikaria-scn/index.html Here is a link to the original article, but it's behind a pay wall. https://www.pnas.org/content/early/2020/03/17/2001045117 Cheers, Tom
  11. S

    D&D scifi, thoughts on the evolution of tech & animals

    So I am writing a campaign for dungeons and dragons, and I have just started putting together a part of the setting in which a kingdom was shrunk about 2000 years prior, and stored in a small container. The upshot of this (by my own authority as the author) is that time travels about 10 times as...
  12. anorlunda

    Night On Earth: Uncovering the Infrared Spectrum of Animals

    I've been watching an interesting nature program on Netflix called Night On Earth. The film was all taken at night using low light and infrared cameras. I was surprised how many animals and insects see well at night. It makes me curious. Do we know how much of the infrared spectrum...
  13. B

    What species does this insect belong to?

    I just found this insect and I don't know what is it. It seems to be the larva of a fly or maybe a little butterfly. I live in Spain so it is fall. What should I do with it?
  14. BillTre

    Was Dickinsonia One of the Earliest Multicellular Animals?

    Multicellular animals (metazoans) are thought (based upon molecular divergence data between metazoanas and chanoflagellates) to have initially evolved about 720 MYA, at beginning of the Cryogenian (720-635 MYA). These first pre-metazoans are assumed to have started out very small with no hard...
  15. J

    Did complex animals evolve at deep sea volcanic vents?

    We see complex animals such as crabs living near deep sea volcanic vents. (Reference: https://ocean.si.edu/ocean-life/invertebrates/hydrothermal-vent-creatures) This is causing speculation that similar life may be living near deep sea volcanic vents on other world such as Europa. Did these...
  16. S

    Do wild animals get matted fur?

    Many domesticated animals like dogs and cats get matted fur and humans take measures to un-mat it. Generally speaking, do non-domesticated animals get mats in their fur? - or are they adapted not to get them or remove them? If they do get mats, are the mats harmful?
  17. mark!

    How does the reward system make animals want to reproduce?

    When in history did our reward system develop, in order to ensure human reproduction? And what drives lower animals to reproduce? Instinct The reward is the survival of the lineage. but do animals know this as well? Do they have some kind of consciousness that they (well, actually not them...
  18. Drakkith

    Visual Acuity of Humans Greater Than Most Other Animals

    According to a paper published back in March, humans see the world with a much higher visual acuity compared to other animals. Cats, for example, have roughly 1/6th the visual acuity of humans, and fruit flies have roughly 1/100th. A few animals do better than ourselves, namely eagles, hawks...
  19. D

    Can Brainless Animals Like Jellyfish and Starfish Learn?

    Hi everyone Are brainless animals such as jellyfish and starfish capable of learning (for example by classical conditioning)? I would have thought not, but apparently there are plants that are capable of learning...
  20. ISamson

    Do animals have life goals or wishes?

    Hello. I know that many humans have lifelong goals, like becoming an engineer, winning the Nobel Prize or something. But do animals have the same? I understand that the goal of all living things is to give a successful and prospering offspring, but do animals and living things other than us have...
  21. mark!

    Add/remove testosterone in animals

    It is well known that, when castrating a rooster it, it won’t be able to exhibit certain male traits (called a ‘capon’). The opposite is also true, when for instance a lioness is injected with testosterone, it will exhibit male traits. Are there more examples known of comparable results, but...
  22. Arman777

    Using Best drone and Software to count wild animals

    I have a project and in that project I'll count the wild life animals from a drone. I need to find a drone that doesn't make much sound also (maximum 60-70 dB), it must capable of a flight time 30 min and also can carry a IR camera. I find a drone callled Phantom 4 (Advanced or Pro)...
  23. anorlunda

    Chaos in flocks & schools of animals

    A documentary on chaos talked about the macro behavior of flocks of birds and schools of fish. They appear organized, but without central command. The documentary said that this is an example of complex behavior arising from simple rules plus chaos. It compared them to the Mandelbrot set...
  24. M

    Non-caloric essential nutrients big vs small animals

    It is true that big animals contain more calories than small animals. However, are the figures for the content of essential nutrients that are not calories different? Such nutrients may be limiting factors and require foraging strategies that would be suboptimal from a simple calory point of...
  25. M

    "Immortal" jellyfish habitat range, Turritopsis dohrnii?

    What is the current habitat range of Turritopsis dohrnii or the "immortal" jellyfish? I know that there are multiple species of the Turritopsis genus and that the species dohrnii have recently increased its range by ballast water spread. What is the current range of the exact species dohrnii?
  26. jim mcnamara

    Names for groups of animals - terms of venery

    https://en.wikipedia.org/wiki/List_of_English_terms_of_venery,_by_animal Lists lots of animals. Clearly people made up some of these things when it was clear nobody really knew if it was correct or not. Heck, we can do that! So let's see what we can come of with: How about a slime of...
  27. stevendaryl

    Reason for different animals' longevity

    Is there a biological consensus about why some species live so much longer than other species? You can sort of understand aging as a matter of the body just wearing out with time. But that doesn't explain why, for instance, dogs go through a similar aging process as humans (gray hair, arthritis...
  28. Timmykuku

    Does Ambient Temperature Affect Cold-Blooded Animals' Size?

    Since cold-blooded animals, such as lizards, turtles, &c., take on the temperature of their environment, can we expect them to linearly and volumetrically expand/shrink in warmer/cooler environments? In addition, can we expect them to follow the simple equation: ΔV=βV0ΔT, for some volume...
  29. mfb

    What is the Significance of Patchwork Viruses in Animals?

    Scientists found a virus that is made out of 4 to 5 separate components - it infects mosquitos, and they have to catch at least four of those components to get infected, the smallest, fifth component is optional. For plants and fungi, similar viruses were known before, but (at least according...
  30. avito009

    How do animals have better immune systems than humans?

    Animals get wet in the rain and still don't fall sick, how is that?. Let's take a stray dog. I have noticed that a dogs nose keeps running and he has to breathe though the mouth. So his immune system has some flaws. Can a human being become so immune just like animals? Tarzan had good imunity...
  31. B

    Do animals experience love or just a chemical reaction?

    Do animals also fall in love? But first.. what is the difference between "in love" and "love?
  32. Stephanus

    Origin of Animals: Investigating the Evolutionary Roots

    Dear PF Forum, Lately I've been watching this channel https://www.youtube.com/user/cassiopeiaproject It's a very good science channel And I've been wondering about this one thing. The origin of animal At first, "life" couldn't do photosynthesys (what ever that we call "life") And at 3.4...
  33. Sophia

    What kinds of dangerous/parasite animals are in your area?

    Summer is almost here and people tend to spend more time outdoors. That is very pleasant and most of us enjoy the sun and warm weather. But there may also be some dangerous creatures, especially in some areas. What are the most common dangerous, venomous or parasite animals in your area? In my...
  34. P

    Do bees know that they will die after they sting?

    This may be an odd question, but it's popped up in many conversations. I know that they die because, aside from losing their stinger, they suffer abdominal rupture too severe to survive. However, it's always seemed odd that they sting out of fear of danger and getting hurt, but they die...
  35. P

    Is Homosexuality in Animals "Abnormal" or Common?

    In the news recently, Filipino boxing star, Manny Pacquiao, spoke of homosexuality as being a sin and against the Bible. He also added that animals did not display such behavior: "It’s just common sense. Have you seen any animal having male-to-male or female-to-female relations? Animals are...
  36. I

    Different animal sensory, short and long term memories?

    Is there any research that was done on animal long and short term memories? And short of empirical analysis, if there is none, is there much we could conclude, based purely on what we know about their brains? For example, from knowing which brain parts deal with explicit and which with...
  37. Necronox

    How can the lift produced by animal wings be calculated?

    Firstly, I'm new to these forums, and I'm not sure what the prefixe in creating this thread is supposed to be... (i'm assuming it is to judge to question's level)? saw some threads without prefixes but i can't post one without... maybe i missed a stickied thread or a readme? Alright, so, first...
  38. klotza

    Scaling Laws and the Speed of Animals - Comments

    klotza submitted a new PF Insights post Scaling Laws and the Speed of Animals Continue reading the Original PF Insights Post.
  39. G

    What animals are good example of natural enemy in PA setting

    I am writing story about Earth set 1000 years in future and I am looking for good example of living animals. So far I had wolves or dogs on my mind, how would they change in 1000 years?
  40. caters

    Fastest animals having similar mitochondria

    I have noticed that cheetahs, peregrine falcons, and sailfish have similar mitochondria as far as amount of base pairs, genes, RNAs, and proteins. Cheetahs have in their mitochondria 17,047 base pairs, 13 genes, 24 RNAs, and 13 proteins. Their speed is up to 75 mph with their acceleration being...
  41. gracy

    The Largest heart among terrestrial animals

    Which of the following is correct 1-Elephant has the largest heart among all terrestrial animals. 2-Giraffe has the largest heart among all terrestrial animals. I have read somewhere that elephant has the largest heart among all terrestrial animals.But now I have seen a book where it is written...
  42. Evo

    Please give if you can to the ASPCA for animals

    I just gave. Give what you can, even a dollar one time it's a single meal. Do what you can when you can, there is no obligation. It's just a one time gift. https://www.aspca.org/secure/donate?linked=1 Please help if you can, if you cant, tell others.
  43. H

    Why Do Land Animals Have Denser Bones Than Sea Animals?

    Given the greater pressure underwater, i.e. at the bottom of the ocean, to survive there youd think that those animals would have stronger/denser bones, but we find that land animals have denser bones to withstand the higher net weight (gravity). But that seems counter intuitive because...
  44. J

    Why do humans see themselves as different from animals?

    While humans are scientifically classified as animals, we frequently see ourselves as being something different from the animals. Why is this?
  45. C

    Animals & Captchas: Can They Be Trained?

    Can some animals be trained to « read » captchas the way they can be to recognize print letters?
  46. C

    What animals have been drawn by this scientist?

    I like animals,my hobbie is drown animals. I used to draw portraits of dogs, cats, parrots ... here are some pictures of me. I draw and print up some http://marioboyshop.blogspot.com/search/label/T-shirt%20For%20Women looks very cute. Here are some pictures that I drew.
  47. K

    ID Kinematics: Chasing a Mouse

    Homework Statement An old fox resting near a road sees a mouse that is traveling at a speed of 1.3 km/h. At the moment the fox sees the mouse , it starts chasing after it . The fox's acceleration is 0.45 m/s^2. a) how much time is elapsed between when the fox start's to when the mouse is...
  48. G

    How do animals use their sense of smell to find water in dry environments?

    If I'm not wrong, several species of animals, for example those living in dry areas of Africa, have the ability to find water many kilometers away. They may be in a dry area with no water around, and say, the nearest small dwell 20 Kms away in North direction, and somehow they can orientate...
  49. T

    On evolution of humans and that of other animals: any discrepancy?

    Question Summary: Do you think human evolution worked in the same way as other living things have evolved through natural selection? Don't you think the human evolution occurred faster than that of any other animals? And humans have possessed too many characteristics ( especially those of...
  50. 256bits

    Porcupine at Animals Wonder in Montana

    http://video.ca.msn.com/watch/video/adorable-porcupine-eats-a-banana/2gv2pvnis?home=en-ca-infopane the guy just loves to look in his basket.