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Prior to the arrival of humans in the Americas, wild ancestors of avocado were consumed and dispersed by Pleistocene megafauna (0.01–1.6 million years ago) such as the giant ground sloths (Megatheridae, Mylodontidae and Megalonychidae) and mastodonlike ancestors (gomphotheres) which roamed western North America and Mesoamerica (Janzen and Martin, 1982; Barlow, 2000; Bost et al., Chapter 2, this volume). It is proposed that these megafauna were attracted to the anise aroma of these fruit that had a high oil content. With the cooling climactic changes in North America at the close of the Pleistocene era, and the loss of most of the potential megafauna involved in seed dispersal of Persea species, the arrival of humans to the Americas (about 13,000 years ago) became an important mechanism for the dispersal of avocado to diverse environments (Barlow, 2000; GalindoTovar et al., 2008). Archaeological evidence suggests that avocado (Persea americana Mill.) was one of the first domesticated tree species in the Neotropics (Smith, 1966, 1969; GalindoTovar et al., 2008). Avocado seeds unearthed and analysed from the Coxcatlán Cave in the Tehuacán Valley, Puebla, Mexico ranged in time period from 7000 to 900 bc (Smith, 1966). Over this period of time, there was an increase in seed size (and by implication fruit size) and a change from seeds with concave to seeds with convex bases (and by implication fruit shape from round to more ovoid or ellipsoid), clearly demonstrating human selection for larger fruit size over time. Furthermore, the archaeological evidence of indigenous tree species throughout the valley indicates that the …