1338: Land Mammals

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Land Mammals
Bacteria still outweigh us thousands to one--and that's not even counting the several pounds of them in your body.
Title text: Bacteria still outweigh us thousands to one--and that's not even counting the several pounds of them in your body.


This comic shows the total weight of mankind and all other land mammals. Only a few centuries ago, humans, their pets and livestock came to make up a great proportion of the earth's land mammal biomass. Note that only land-dwelling mammals are taken into account, so for instance whales and sea cows will not be included. (Whether this only covers animals that cannot live on land or any marine mammals like for instance seals and walrus, is not clear).

The design of the blocks loosely resembles a cell. This could be a reference to how these animals support humans, analogous to a cell supporting a central nucleus. If so, it seems that all the animals in this diagram, wild or domestic, in some way support human activity.

The title text states that bacteria outweigh us thousands to one, without counting the several pounds of bacteria in our body that are considered part of our own weight (like Gut flora). The aforementioned cell could also be a bacterium, making it a possible reference to the title text, since 1256 blocks have been used to sketch the "cell", and bacteria outweigh us by about this factor.

This comic may be a nerd snipe from Randall, challenging his readers to figure out the missing parts.

Randall also discusses animal biomass in Fairy Demographics in which he compares the biomass of "fairies" to humans, horses, and humpback whales.


According to the diagram, there are 358 million tons of humans, 864 million tons of pets and livestock, of which 520 million tons comes from cattle, and 34 million tons of wild animals; for a total of 1.256 billion tons. The number of blocks represents the weight of the group in millions of tons = billions of kg. Note that some entries have the same number of blocks, and thus have the same rank.


Cattle, in aggregate, are much heavier than the human population. Humans outweigh both sheep and pigs put together. This may be a surprise for people in the countries that produce the majority of meat from such animals, because here these animals outweigh the population. But there are many parts of the world where especially pigs are not eaten, and it is not every where that sheep is in great demand. And especially in the some of the most populations dense regions in the Third World meat is not something you can afford to eat on a regular basis.

Our pets and livestock[edit]

There are 13 distinct blocks of pets and live stock; only the top 5 are labeled - in order of weight they are: Cattle, Sheep, Pigs, Goats and Horses. Cattle, in aggregate, are much heavier than the human population, which has been inserted in the table for comparison:

Total Rank Weight  (Millions of tons) Name
1 520 Cattle
2 358 (Humans)
3 135 Sheep
4 90 Pigs
5 39 Goats
6 29 Horses
7 13 Unlabeled
9 8 Unlabeled
10 7 Unlabeled
10 7 Unlabeled
13 6 Unlabeled
14 5 Unlabeled
17 3 Unlabeled
19 2 Unlabeled

Wild Animals[edit]

There are 8 distinct blocks of wild animal (elephants and 7 others). The elephant is the only type of wild animal to be singled out in the comic. This may possibly be due to elephants being the largest land mammal. And yes, the world's heaviest land animal only takes up one square. Also interesting is that the largest group of wild animals only comes in on a tied 8 place in the ranking (which is shared between the two tables).

Rank Weight  (Millions of tons) Name
8 10 Unlabeled
10 7 Unlabeled
14 5 Unlabeled
16 4 Unlabeled
17 3 Unlabeled
19 2 Unlabeled
19 2 Unlabeled
22 1 Elephants


The comic references the book The Earth's Biosphere: Evolution, Dynamics, and Change by Vaclav Smil as the source for most of the data. A few other sources have also been used, but were not referenced. On page 186 of Smil's book, there is a bar chart with the following values:

(Millions of tons) Name
0.8 Elephants
40 Horses
100 Pigs
450 Cattle
280 People
80 Whales
30 all wild vertebrates
650 all domesticated vertebrates

Note that all labelled non-human animals are in this table. It seems that this table was the source of most of the data in the comic. Only land dwelling mammals are taken into account. Whales, wild vertebrates, and domesticated vertebrates are not included in the comic.

Unlabeled Animals[edit]

These are guesses about the identity of the unlabeled animals

Rank Comic weight (Millions of tons) Type Guess Actual Population (Millions) Average Weight (kg) Total weight (Millions of kg) Explanation
7 13 Pets/Livestock
8 10 Wild animals
9 8 Pets/Livestock
10 7 Pets/Livestock Camel 17 412 7004 Wikipedia lists the number of camels as 17 million. An average weight, based on Wikipedia's numbers for male and female, is about 500 kg. So, including the non-adult camels, an average around 400 kg seems to be a realistic estimate.
10 7 Pets/Livestock
10 7 Wild animals
13 6 Pets/Livestock Dogs 400 15 6000 According to Wikipedia, there are 400 million dogs worldwide. If the average weight is 15 kg, there would be 6 blocks.
14 5 Pets/Livestock Donkeys 41 122 5002 There are roughly 41 million donkeys on Earth, with an average weight of about 125 kg.
14 5 Wild animals
16 4 Wild animals
17 3 Pets/Livestock
17 3 Wild animals
19 2 Pets/Livestock Cats 500 4 2000 There are 500 million domestic cats worldwide. The average weight of an adult cats is 4.5 kg. Factoring in the lighter weight of immature cats, 4 kg as an average for all cats, (adult and immature) is within the range of possibility. (According to 526: Converting to Metric cats do weigh 4 kg, only with caption do they reach 4.1 kg).
19 2 Wild animals
19 2 Wild animals Rat 4000 0.5 2000 The World Health Organization estimates 4 billion rats[citation needed] worldwide. The average weight of an adult rat is under 500 g.


[Caption at the top of this chart:]
Earth's Land Mammals by Weight
[Below the caption is a light gray block with a label (in light gray as well) to indicating the value of each block:]
= 1,000,000 tons
[Below this there is a row with three blocks each in a different color, dark and light gray and green, each block is labeled to the right:]
Our pets and livestock
Wild animals
[The rest of the comic consist of a chart with different groups made up of these individually and differently colored blocks, each grouping representing the weight of a different mammals, except the center part, the only one with dark gray block, which represent humans. The largest group to the left is the only one larger than the humans group in the center. There are 22 groups in total, 1 human group with 358 dark gray block, 13 groups of light gray with a total of 864 blocks and 8 green groups with a total of 34 blocks for a total of 256 blocks. Both the light gray and the green groups are spread out on all sides of the human center group. Only difference is that all the green are on the very outside, whereas some of the smaller light gray groups are close to the core, far from the outside. The five largest groups of light gray blocks are labeled, as well as the smallest group consisting only of a single green block. All the labels has a line pointing to the relevant group and all of them are on the outside of the entire block. Going clockwise from the top left the labels are:]
[At the bottom right of the comic is the following gray text with a reference:]
Data from Vaclav Smil's The Earth's Biosphere: Evolution, Dynamics, and Change, plus a few other sources.

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Is it mass or weight? -- 06:38, 5 March 2014 (UTC)

It says weight. Since most land animals live on the... land, there is not much difference. I suppose if a lot of aninimals lived near a prime pole vaulting location it could skew the results. 06:40, 5 March 2014 (UTC)
Ton is a unit of the quantity mass, not weight. Weight is a force and forces would be measured in newtons. Hence the comic is making a mistake. One that 99% of the people do. Mass would be correct since it is a more fundamental quantity and is usually what is meant when people talk about weight. 18:29, 9 March 2014 (UTC)
Ton is actually a unit of weight, at least assuming the comic is using the short ton (widely used in the US). 1 ton = 2000 pounds, and pounds are a unit of weight. A metric ton, tonne, and long ton are units of mass, defined as a quantity of kilograms. 18:32, 26 September 2014 (UTC)
No, pound is a unit of mass as well. The pound-force is a unit of force. One pound-force is the amount of force exerted by Earth's gravity (under certain conditions, I have no idea which) on a pound of mass.Tharkon (talk) 20:37, 4 October 2014 (UTC)
Because of the "historical conflation of mass and weight", it's now more precise to use the term "pound-mass" for the unit of mass. ArtDuck (talk) 22:52, 24 October 2014 (UTC)
No, you're all wrong. Pound is a currency. 15:40, 7 October 2014 (UTC)
Based on his comments on the subject in a What If comic, I strongly suspect that he doesn't care about the distinction in cases where: a) the values of the measurements are equal, and b) it's just a comic, not a research paper. Marcus Erronius (talk) 17:42, 20 September 2014 (UTC)

Weight and mass are synonyms for most people. For example Random House Dictionary says about weight:

1. the amount or quantity of heaviness or mass; amount a thing weighs.
2. Physics. the force that gravitation exerts upon a body, equal to the mass of the body times the local acceleration of gravity: commonly taken, in a region of constant gravitational acceleration, as a measure of mass.

Xhfz (talk) 23:54, 30 August 2015 (UTC)

I'm really curious, what are the other, unlabeled groupings? Author's website (talk) (please sign your comments with ~~~~)

Velociraptors, I'd assume. 09:50, 13 October 2014 (UTC)

On page 186 of Smil's referenced book, there is a bar chart with the following values in millions of tons (*=not used in Randall's graphic):

elephants 0.8
horses 40
pigs 100
cattle 450
people 280
*whales 80
*all wild vertebrates 30
*all domesticated vertebrates 650 (talk) (please sign your comments with ~~~~)

I think that this graph is actually more illustrative of how much support humans need to maintain themselves (the amount of cattle is astonishing). lcarsos_a (talk) 07:58, 5 March 2014 (UTC)

need? I don't think we need so much cattle. It's just that most people prefer hamburgers and steaks to beans. So, how much we use to maintain ourselves would be better. (BTW, you don't count yourself as human?) -- Hkmaly (talk) 10:39, 5 March 2014 (UTC)
According to [1] there are 525 million dogs, assuming 20 kg as average weight, this should give 10 squares in the diagram. I can't find reliable numbers for cats, but there are more cats than dogs, but they don't weigh as much, so their total weight could be similar to that of the dogs. -- 08:42, 5 March 2014 (UTC)

The blob of 13 under the word Livestock may very well represent both dogs and cats. (talk) (please sign your comments with ~~~~)

Layout of the blocks

Does anybody see a reason for the particular layout of the blocks? My first impression was a globe but obviously it doesn't correspond to any continents, etc. 08:44, 5 March 2014 (UTC)

I've been wondering myself... I do think it is a picture of something. My ideas so far: an eye, a fried egg, a cell. --Divad27182 (talk) 09:29, 5 March 2014 (UTC)
It may simply be something-like-a-circle of humans with the rest surrounding it. But it DOES look like a cell. -- Hkmaly (talk) 10:39, 5 March 2014 (UTC)
Could it be a sort of relationship diagram? It looks like we're in the centre, with the animals we have the closest relationships with — our pets and our food — nearest, and those we're less concerned with further away. Gidds (talk) 11:34, 5 March 2014 (UTC)
Yes, the overall layout is human-centric, but that doesn't explain the intentionally lumpy and asymmetric regions. It would have been easier to place the blocks in regular shapes (circular, rectangular or otherwise) but Randall chose to do it this way. Cell with a nucleus is a reasonable guess. - Frankie (talk) 14:00, 5 March 2014 (UTC)
I think it resembles a (low resolution) globe, with humanity representing the major continent Boxy (talk) 14:19, 5 March 2014 (UTC)
I think it shows the relationship of the title text (assuming we are part of land mammals): there are about 1.2K squares in total representing a factor of 1K:1 overall. Thus the shape (resembling bacterium) is explained, the incorporation of all mammals into the shape, and the potential central location of humans (assuming most bacteria lives in our gut). 16:09, 5 March 2014 (UTC)
I'm thinking the data points are placed using a polar coordinate system (although what the axis are I don't know, other than that being human gets you close to the center) combined with a mapping onto an x-y grid. Does that make any sense? --RenniePet (talk) 20:56, 5 March 2014 (UTC)
I think the layout is intended to show two legged mammals in the middle and four legged surrounding it. There are not sufficient six legged mammals to make yet another circle outside the four legged circle. Spongebog (talk) 16:47, 6 March 2014 (UTC)
You know of ANY six legged mammal? Any six-appendages vertebrate I know of is mythological creature (like pegasus or some dragons) or non-earth origin (like tree cats or Pandora-native). -- Hkmaly (talk) 10:58, 7 March 2014 (UTC)
I think we humans are afraid of the wild animals, and are huddling in the center and have either gathered the domesticated animals around us to protect us, or they have surrounded us on their own to protect us. Chrullrich (talk) 07:51, 20 September 2014 (UTC)
Is it just me or is that a tip view of the human skull with eyes pointing left? Perhaps something about the placement indicates where we place the importance of these species in our minds? Wild guess and all that? -- Sean timmons (talk) (please sign your comments with ~~~~)

Don't think there is anything to the layout, other than making it fit as a evenly distributed in a circle, placing the wild species near the domesticated relatives -- my vote is to remove the layout from the incomplete tag Spongebog (talk) 21:48, 21 September 2014 (UTC)

Identifying the groups

I would love to identify specific groups. The unlabelled animals come in groups, even the wild animals, even though only *one* of those groups (elephants for some reason) has been labelled. —TobyBartels (talk) 13:05, 5 March 2014 (UTC)

Reason for elephant label == "This is how much/little the whole population of the largest land mammals amass to."? (Actually, given the scarcity of elephants, I'm surprised it's a full block. I suspect something else that could have been labelledsuch as "rats" would be far more.) 14:07, 5 March 2014 (UTC)

Per the wikipeda page[2] on camels I expect that they are the blob of 3 gray squares. Mwiser (talk) Update: I hadn't seen the 1 billion kg == 1 million tons notation which has since appeared. I therefore added camels (and also donkeys) to the table below. Mwiser (talk)

Non SI units should just die already. 20:39, 5 March 2014 (UTC)

Is Randall's ton the metric tonne or the US short ton? -- 22:06, 5 March 2014 (UTC)
Considering that Randall is very aware of the SI confusion, I'm sure he would have made it clear if he where NOT using metric tonne - so I would say his tonne is 1,000 kg! Kynde (talk) 08:53, 6 March 2014 (UTC)
Considering that he's in the U.S. & he didn't specify "metric ton" or spell it "tonne" I'd assume the 2K lbs. American ton -- so maybe it's hard to say for sure! ¯\_(ツ)_/¯ But are the data even precise enough to draw this distinction at all, or is it drowned out by yearly fluctuations & sampling errors anyway? -- 03:35, 12 October 2018 (UTC)
Stab at the numbers
Land Mammal population in Billions Average Kilograms Total Kilograms in Billions xkcd value Notes
Humans 7.2 70 504 358 as of 2013
Cattle 1 1740 1740 520 as of 2012
Pigs 1 350 350 90
Chickens 19 1 19 not mammals
Goats 0.865 46 39.7 39 as of 2008... src
Sheep 1 80 80 135
Elephants 0.000105670 5000 0.5 1 as of 2012 src
Horses 0.058372106 500 29 29 as of 2006 src
Rats 10 0.35 3.5 2 10B is a guess
Cats 0.6 5 3 2
Dogs 0.4 40 16 6
Seal 0.022 200 4.4 not a land mammal
Mole 0.075 Numbers are slightly exaggerated, but it would be nice to have those quantities
Krill  ?  ? 175-725 Wild species with largest biomass (not a land mammal)src
Camel 0.014 465 6.51 As of 2010 src
Donkey 0.04 160 6.4 As of 206 src mass src 16:19, 5 March 2014 (UTC)

Talk about the table
uhh.... chickens aren't... mammals? (?) Brettpeirce (talk) 17:22, 5 March 2014 (UTC)
Apparently not. http://www.ask.com/question/are-chickens-mammals --RenniePet (talk) 03:23, 6 March 2014 (UTC)
fixed 19:39, 11 March 2014 (UTC)
Where does these XKCD numbers come from? Cattle 1740? Humans 556? According to the comic there are 520 Cattle and 358 Humans (million ton). This table makes no sence in the XKCD number department. Appart from that it would be a great table to include in the comic... Kynde (talk) 08:52, 6 March 2014 (UTC)
fixed 19:39, 11 March 2014 (UTC)
Where does the average weight come from? As the human race is very young (26% below 15 years) and the cattle population has is changed very rapidly - thus there will also be many calves all the time - reducing the average weight far below that of an average adult animal ready to made in to beef... Kynde (talk) 09:55, 6 March 2014 (UTC)
Click on the wiki links below the table and a few more clicks you will find the numbers... add direct source links if you like 19:39, 11 March 2014 (UTC)
Maybe the seal is considered a land mammal by Randal? Only wales are really not land mamals. The link to elephant population seems only to cover African elephants not Asian... Kynde (talk) 11:01, 6 March 2014 (UTC)
Does Randall consider cattle to be all the genus Bos? Waterbuffalo for example weigh about 400kg and wikipedia claims a world population of 130M. That would be 52 blocks. So, I'd assume that since there aren't any free blocks that large, that they are considered cattle. So, then Yaks and Wildebeests should be considered cattle as well, no? 22:06, 7 March 2014 (UTC)rbnm
Sorry I meant Tribe Bovini not genus Bos
Rodentia? If the average rodent weighs something like 0.67kg, then 15B rodents would make up 13 squares. 0.67kg comes from the log average of the smallest and largest. If this includes rats (4B per the WHO) - is it reasonable that the rest of Rodentia includes 11B, 1-2 rodents per person on the Earth? That would include: squirrels, porcupines, beavers, guinea pigs, and hamsters; although guinea pigs might be considered pet/livestock (mmm... cuye!). 23:56, 7 March 2014 (UTC)rbnm
Title Text

The title text mentions that bacteria outweigh humans by thousands (plural) to one. The notation 1000:1 used in the explanation is therefore not correct.

True - I did not spot that. I have corrected it to the same version as the title textKynde (talk) 19:15, 6 March 2014 (UTC)

This mammals belong to "Pets/Livestock" and "Wild animals". Any ideas where this does fit in here? --Dgbrt (talk) 23:47, 9 March 2014 (UTC)

There are several other animals where there could be both a wild and a domesticated (or pet) version. Foes Zoo animals count as pets? Elephant is a good example as they are domesticated in India. Is domesticated only animals where we have changed them - like cows and pigs? In that case the elephant is not domesticated - as it has not been breed into a different race... -- Kynde (talk) (please sign your comments with ~~~~)

This belongs to "Wild animals". Any ideas where this does fit in here? --Dgbrt (talk) 23:52, 9 March 2014 (UTC)

Smil table

he singles out elephants in the table, and uses Mt of Carbon as a unit. The % of carbon is ~18,5% in humans (I guess this is pretty average for mnammals too, so checking the numbers should take this in to account.

Guessing the unlabeled groups is a pretty futile exercise, are yaks cattle or not, what of reindeers, are both camels and llama and alpacas marked separately. largest wild is likely though rodents, and the smallest likely all wild carnivora. odd-toeds, even-toeds, marsupials, all other mammals are some other likely groups in the 'wilds' section. 04:40, 26 March 2014 (UTC)

Anyone in the US want to spend a few dollars to try and clear up these unlabelled groups? The book used by Randall in creation of this comic is available on amazon. --Pudder (talk) 15:55, 1 October 2014 (UTC)

Revised Article Requirements

Many people have taken a significant amount of time to figure out what animals are part of what group. Clearly this is not possible without a significant amount of interpretation. I am removing this "need" so that this article can be marked completed at some point in time, preferably before the Sun burns out. 20:27, 20 October 2014 (UTC)