* How easy? Large mammals like horses are so great at moving both humans and goods over terrain that they’ll remain the gold standard option for land transport all the way until the invention of railroads, and the gold standard option for military transport right up until the invention of trucks and/or tanks. Plus, many large mammals can transform vegetables you can’t digest (like grasses) into delicious milk that you can (assuming you have the right enzymes; see Section 8.5). The recurring calories these animals provide from milk alone greatly outweigh the one-time calories you get by eating their meat.