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.

[edit] Explanation

Ambox notice.png This explanation may be incomplete or incorrect: The division of animal blocks are clear but only 6 are labeled. Some qualified guesses as to how the other (at least the largest) blocks are divided should be possible... What about the layout of the blocks?
If you can address this issue, please edit the page! Thanks.

This comic is a Nerd Sniping by Randall to his viewers. This explain tries to figure out the missing parts.

The comic shows the total weight of mankind and all other land mammals. Only a few centuries ago humans, and their pets and livestock, come to occupy such a great proportion of the earth's land mammal mass.

Per 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 1.3 billion tons.

As of March 2014, the world population was about 7.16 billion people1 and so the comic assumes an average human weighs 50 kg: 7.16 billion people × 50 kg = 358 billion kg = 358 million tons. The BMC Public Health 2012 (12:439) article "The weight of nations: an estimation of adult human biomass" estimated the average adult weighed 62.0 kg (Table 3), but the authors noted that their work "did not estimate the bio-mass in children who comprise a significant proportion of the population in many countries". The 50 kg estimate in this comic includes the 25% or more of the worlds population below 15 years of age making the 12 kg reduction a credible adjustment.

Cattle, in aggregate, are much heavier than the human population, but we do manage to outweigh both sheep and pigs - which may come as a surprise - as these animals probably by far outweigh the population in the countries that produce the main part of the worlds meat from such animals.

It is interesting to note that the world's heaviest land dwelling animal - the elephant - only takes up one square! It is the only type of wild animal to be singled out in the comic.

There are 8 distinct blocks of wild animal (elephants and 7 others). 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). Dogs would properly also take up a large part - but how detailed are the division of species...?

Water buffalos seem to be missing completely. According to Wikipedia, there are 172 million of them with a weight of 300–550 kg each. With an average between 300–400 kg (depending on the number of calves) there is 50-70 million tons of them - giving them a much larger weight than goats, which would put them in fifth place in the table below.

The comic references the book The Earth's Biosphere: Evolution, Dynamics, and Change by Vaclav Smil as the source for most of the data - although a few other sources has also been used. These other sources are not referenced.

Note that only land dwelling mammals are taken into account - thus no whales. It is not clear as to where, for instance, seals, sea lions and walruses belong - although they could belong to land mammals as they spend a lot of time on land - as opposed to whales.

All other types of animals are not included. For instance, the weight of insects would outweigh us by far. Although not as much as the bacteria mentioned in the title text - they outweigh us thousands to one.

And that is without counting the part of our body weight that consist of bacteria: Several pounds. A fact that most people would properly like to ignore - which is a good reason to mention it here. These pounds are already counted as part of the total human weight.

There has been some speculation about the design of the blocks. They could be seen as resembling a cell (a bacterium). An extra joke in this could be that a little more than thousand blocks representing mammal weight has been used to sketch this bacterium and bacteria outweighs the mammals on this order.

[edit] Table of the block sizes

  • The table below ranks each group of blocks from 1 to 22 according to the size of the group = the number of blocks. The number of blocks represents the weight of the group in millions of tons = billions of kg.
  • The comic contains a total of 1256 blocks in three colors representing the 1.256 billion tons of land dwelling mammals.
    • 358 million tons from humans - dark grey color
    • 864 million tons from mammalian pets and livestock - light grey color
    • 34 million tons of wild land dwelling mammals - green color
Feel free to enter a comment on the groups especially those that are not already identified.
The population should only be be stated (in millions) if it can found through references - the XKCD average weight (in kg) is then given from the number of blocks in the group.
Rank # Blocks Type Text Population (millions) Weight (kg) Notes/comments
1 520 Pets/Livestock Cattle 1000 520 They only outweighs us by weight - not by numbers - there has been a stable population of about 1 billion cattle since 2007.
2 358 Humans 7152 50.1 According to the U.S. Census Bureau's population counter, there were 7.1516 billion people in the world as of March 4, 2014.
3 135 Pets/Livestock Sheep 1000 135 There are about 1 billion sheep according to Wikipedia. The average sheep weight of 135 kg seems highly exaggerated as only the rams can weigh more than that.
4 90 Pets/Livestock Pigs 1000/2100? 43/90? According to Wikipedia, the population of pigs is about 1 billion. According to the 2nd reference given for this in the wiki article, there is, however, 1.3 billions, and then 0.8 billion more (probably piglets) for a total of 2.1 billion? The piglets will not weigh much though.
5 39 Pets/Livestock Goats 864 45 The goat population can be summed to 864 million from Wikipedia's goat article. According to this list there are 850 million goats.
6 29 Pets/Livestock Horses 58 500 According to Wikipedia there is a population of 58 million horses. Horses can weigh from 400-1000 kg. There are probably not that many foals compared to adults, as for instance for cattle and pigs.
7 13 Pets/Livestock
8 10 Wild animals The largest grouping of wild animals, less than 1/50 of the weight of cattle - although representing almost a third of all the wild land mammals.
9 8 Pets/Livestock
T10 7 Pets/Livestock Camel? 17 412 Wikipedia lists 17M as the number of camels. An average based on Wikipedia numbers for male and female is about 500 kg. So including the non-adult camels an average around 400 kg seems as a realistic estimate.
T10 7 Pets/Livestock
T10 7 Wild animals
13 6 Pets/Livestock Dogs? 400 15 According to Wikipedia, there are 400M dogs worldwide. Assuming an average size at 15 kg, gives 6 blocks. Small dog=2 kg large dog = 100 kg the log average is about 15 kg.
T14 5 Pets/Livestock Donkeys? 41 122 There are roughly 41 Million donkeys on earth and the average weight is about 125 kg
T14 5 Wild animals
16 4 Wild animals
T17 3 Pets/Livestock
T17 3 Wild animals
T19 2 Pets/Livestock Cats? 500 4 Wikipedia quotes 500M domestic cats worldwide, with an average weight of 4.5 kg. So with kittens 4 kg may seem very realistic.
T19 2 Wild animals
T19 2 Wild animals Rats 4000 0.5 A rat in the wild seldom weigh over 500 g. WHO estimate of 4 Billion rats (citation needed) and a comparable number of mice (The House mouse weighs only about 20 g and mice would thus only fill 0.08 block).
22 1 Wild animals Elephants 0.75 1300 The only wild animal to be singled out with text - also the heaviest land dwelling animal - but still only take up one block. According to Wikipedia the wild poulation of the African elephant is around 700,000 (decreased from 1.3 mill in the 90s). For the Asian elephant it is as low as 40-50,000. For a total of 750,000 individuals. Any animals in the zoo or domesticated Asian elephants should not be counted. As adult African female elephants (who is probably the most abundant) weigh 2-3 ton, 1.3 ton seems a little low, especially since there is not a lot of calves as the elephants have a long lifespan. However, even with an average weight of 2 ton, the total weight would only be 1.5 million ton, and could be rounded down to 1 block...

[edit] Transcript

Earth's LAND MAMMALS by weight
[A block indicating the value of each block:] = 1,000,000 tons
[Dark gray block:] Humans
[Light gray block:] Our pets and livestock
[Green block:] Wild animals
[The rest of the comic consist of blocks representing the weight of mammals. Some of the blocks are labeled:]
  • Cattle
  • Pigs
  • Goats
  • Sheep
  • Elephants
  • Horses
Data from Vaclav Smil's The Earth's Biosphere: Evolution, Dynamics, and Change, plus a few other sources.
comment.png add a comment!


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)

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

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 ~~~~)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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

[edit] 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)

[edit] Rabbit

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 ~~~~)

[edit] Deer

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

[edit] 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)
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