For the acquired response to "remember" and eliminate a large number of pathogens the immune system must be able to distinguish between many different antigens, and the receptors that recognize antigens must be produced in a huge variety of configurations, in essence one receptor (at least) for each different pathogen that might ever be encountered. Even in the absence of antigen stimulation, a human can produce more than 1 trillion different antibody molecules. Millions of genes would be required to store the genetic information that produces these receptors, but, the entire human genome contains fewer than 25,000 genes.