The article explores how many different species of animals there are on Earth and how new species are formed. By combining two different theories, the researchers estimated the number of species based on body size and diet. They found that larger animals have lower speciation rates, and carnivores create new species faster than herbivores or omnivores of the same size. The total number of terrestrial animal species is estimated to be between 1.03 and 2.92 million. This new approach could help us better understand and predict changes in global biodiversity as the world faces significant environmental challenges.