Although significant debate exists as to how much human predation and indirect effects contributed to prehistoric extinctions, certain population crashes have been directly correlated with human arrival.
[17][23][33] A 2018 study published in
PNAS found that since the dawn of human civilization, 83% of wild mammals, 80% of marine mammals, 50% of plants and 15% of fish have vanished. Currently, livestock make up 60% of the
biomass of all mammals on earth, followed by humans (36%) and wild mammals (4%). As for birds, 70% are domesticated, such as poultry, whereas only 30% are wild.
[49][50]