A handful of lending start-ups are making near-instant underwriting decisions using sophisticated software that can learn to make "better" loans based on thousands of pieces of borrowers’ information. The start-ups, including personal lender Earnest and payday lender ZestFinance, hope to transform the economics of underwriting, making more loans available at lower cost. By law, lenders cannot discriminate against loan applicants on the basis of race, religion, national origin, sex, marital status, age or the receipt of public assistance. But as startups rely increasingly on complex software algorithms that work autonomously and learn as they go, some worry that the machines could end up discriminating against certain groups without being explicitly programmed to do so.