A possible scenario for the origin of elementary hexoses (fructose, glucose, mannose, and galactose) has been presented (Hirabayashi 1996). The scenario suggests that the formose reaction, starting with formaldehyde (CH2O) forms the foundation of carbohydrate chemistry. The process includes key reactions, such as aldol condensation between two trioses, glyceraldehyde and dihydroxyacetone, which produces ketohexoses, including fructose. Once the fructose is produced, it undergoes the Lobry de Bruyn–Alberda van Ekenstein transformation to produce the corresponding aldohexoses, glucose and mannose, which emerged during chemical evolution. While it remains an open question how these elementary hexoses were accumulated on a prebiotic Earth, glucose is considered the most stable monosaccharide and is thus regarded as the primary substrate for “bricolage” in the subsequent biological evolution. Among these products is galactose, which results from the invention of a 4-keto-intermediate of UDP-Glc, facilitated by NADH (coenzyme). This mechanism enables both reduction and epimerization at the C3, C4, and C5 positions. From a biological recognition perspective, galactose is unique due to its axial configuration of the C4-OH group (referred to as 4-epi-Glc), which sharply distinguishes it from other major monosaccharides, such as glucose and mannose (2-epi-Glc). Moreover, as a “late-comer” saccharide in contrast to glucose and mannose, galactose is frequently positioned at the outermost regions of glycoconjugates. These characteristics likely offered multicellular organisms advantages in navigating complex cellular communities. The structural heterogeneity originating from the positioning of galactose in glycans might be further amplified by the diversification of galactose modifications, including sialylation and fucosylation—both of which are biosynthesized from mannose in modern biosystems. Glycosyltransferases for these late-comer saccharides (galactose, sialic acid, and fucose) are located downstream in the biosynthetic pathway, specifically in the Golgi apparatus. The hetero-geneity of galactose-containing epitopes likely co-evolved with the carbohydrate-recognition proteins that decode them. Among these, galectins are distinctive because, unlike most lectins, they are stored in the cytoplasm, typically isolating them from their target ligand under normal conditions. Furthermore, their sugar-binding specificity is largely restricted to β-galactosides, typically N-acetyllactosamine. However, galectins also exhibit a remarkable ability to decode the galactose-driven glycan heterogeneity for various biological functions. In this review, we explore the origin of galactose, the specificity and biological functions of these “avant-garde” lectins, and introduce galectin-driving liquid–liquid phase separation and its roles.