Weigh every wild mammal on Earth
Put every wild mammal on Earth on one side of a scale — every elephant, whale, deer, mouse, bat, lion, otter, kangaroo, rat, wolf, bear, and wildebeest alive today. Put humans and our livestock on the other. The wild side holds just 4% of the weight1.
The other 96% is us and the animals we breed to eat. That’s the headline of the first comprehensive census of life on Earth, completed in 2018 by researchers at the Weizmann Institute and Caltech.
of Earth's mammal biomass is wild. The other 96% is humans and our livestock.
Why this number sits still
This is one of the few counters on the site that shows a flat number — the same at every visit. The Bar-On census is a one-time snapshot, and no comparable measurement has been repeated. Extrapolating from related indices (like the Living Planet Index’s 73% population decline) to a projected biomass share would be guesswork dressed as data. So we show the measured 4% plainly and leave projection out. When the census is repeated, we’ll update both the number and this note.
The weigh-in
The Bar-On census reported global mammal biomass as:
- Livestock: 0.10 gigatonnes of carbon (Gt C) — dominated by cattle and pigs
- Humans: 0.06 Gt C
- All wild mammals combined: 0.007 Gt C
That’s all wild mammals — every elephant, whale, deer, mouse, bat, lion, otter, kangaroo, rat, badger, fox, bear, wildebeest, and primate on Earth, summed by their living biomass. Together they weigh less than one-tenth of the world’s livestock.
The picture for birds is similar: domestic poultry (mostly chickens) make up roughly 2.5 times the biomass of all wild birds on Earth combined.
Why weight, not headcount
Biomass — the total living weight of a group — captures ecological footprint better than species count. There are about 5,400 mammal species; only a handful are domesticated. But those few species, multiplied by the billions, dominate the planet’s ecology by sheer mass. A measurement based on species would say “humans have domesticated 0.1% of mammal species.” A measurement based on biomass says “humans and their domesticates are the planet’s mammal life now.”
This is what the Anthropocene looks like at the scale of weight on the ground.
From majority to remnant
Nobody was weighing cattle against tigers in 1750, so precise figures for earlier centuries don’t exist. But the shape of the trajectory is clear enough. Fifty thousand years ago, in the late Pleistocene, wild giants ruled — mammoths, mastodons, giant ground sloths, woolly rhinos made up the bulk of mammal weight on the planet. By the eve of industrial agriculture around 1750, domesticated animals were already significant across Europe, the Americas, and Asia, yet wild mammals were probably still the majority — rough estimates put their share near 30%. Then, in 2018: 4%.
Almost all of that collapse — from roughly a third to a twenty-fifth — is a 20th-century story, written by the industrial expansion of livestock. The 30% starting point is an order-of-magnitude estimate drawn from FAO historical livestock records, not a survey, and we treat it as such. The 4% endpoint is the measured one.
Same land, different use
The Living Planet Report 2024 puts the proximate cause concisely: habitat loss and degradation driven by agriculture and food systems is the single largest driver of monitored wildlife population decline3. The same agriculture that produces the livestock is what’s converting the habitats that wild mammals used to live in. The two trends are not independent — they are the same trend, viewed from two sides.
The LPI tracks the population side of this collapse — average wildlife populations have shrunk 73% in 50 years.
What 4% leaves out
Biomass is not the same as ecological function. Wild mammals weigh less, but they still pollinate, disperse seeds, fertilise soils, prune vegetation, and structure food webs in ways that livestock — penned, fed, slaughtered young — do not. The 4% figure is alarming but it understates the ecological collapse: a kilogram of wild boar in a forest does work that a kilogram of domestic pig in a feedlot does not.
The number also doesn’t capture trajectory. The Bar-On census is a snapshot in time. The Living Planet Index measures the trend in population sizes — separate methodology, same direction.
The number under all the others
The site’s other wildlife counters — birds in decline, insects collapsed, species at extinction risk — describe the trend. This one describes the state. As of 2018, the wild mammal share of mammal biomass on Earth sat at 4%, and the broader indicators since suggest the share has only continued to fall.