New research has shown that since humans evolved from the species Homo erectus to today, the size of mammals all over the planet has been getting smaller. This is the direct effect of human expansion, from which big mammals have been suffering more.
Jacob Dembitzer, Ran Barkai, Miki Ben-Dor, and Shai Meiri, all from Tel Aviv University in Israel, have published an article in the Quaternary Science Reviews titled “Levantine overkill: 1.5 million years of hunting down the body size distribution.” In it, they show lots of evidence for this decline in mammal size in the Eastern Mediterranean, which matches results across the world. They found that over the last 1.5 million years, since our ancestors Homo erectus began to expand beyond Africa, the mean mass of hunted mammals decreased by more than 98%. This is because humans hunted the biggest mammals to extinction.
Until around 20,000 years ago, most mammals were bigger than humans, but since then most have been smaller. When farming began around 12,000 years ago the average mass of mammals was around 30 kilograms (about half a human). This destructive effect of human presence can be used to estimate the dates humans first arrived on different continents, as it matches the timings of big mammal extinctions. The average size has been declining because most of the large mammals went extinct, especially across America and Australia. Humans evolved in Africa, so the large mammals in our home continent had learnt to protect themselves from humans or had already gone extinct earlier, but the big mammals of other continents had no time to adapt to humanity’s destruction tsunami.
Today, little has changed. Many large mammals are among the most endangered vertebrates on Earth, especially due to advances in technology that allow trophy hunters to travel from all over the world, and from the safety of a vehicle, mercilessly kill the big African mammals who no longer have effective ways to avoid humans. This extinction risk for the largest mammals gets worse by the fact that they have much slower reproduction times than smaller animals, so nature cannot cope with such hunting pressure. If we fail to ban trophy hunting, bushmeat, and wildlife trade, and we do not stop — and reverse via rewilding — wild habitat loss, we are likely to continue the pattern of the past, and the elephants, rhinos, giraffes, polar bears and gorillas will be the ones to go first. It’s time to take the next evolutionary step into a vegan humanity as, otherwise, the Earth would become a very lonely place.