It has been proposed that ASR using maximum likelihood methods is biased towards predicting ancestors with enhanced thermostability . However, the trends seen here in lineages leading to thermophiles suggest instead that any such bias is likely to be small relative to the trends related to evolution of biological niche (i.e., meso-to thermophile). This implies that it is not necessarily feasible to obtain a more thermostable enzyme simply by inferring and resurrecting ancestors of a group of extant sequences without considering the possible evolutionary pathway in the context of the biological niche of the extant enzymes. Rather, as shown by comparison with other studies , candidate families for which this strategy is most likely to succeed are those where there has been broad diversification of enzymes in a protein family from a common ancestor in mesophiles, leading to large extant families with diversified functions.