Maize: Origin, Domestication, and its Role in the Development of Culture

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Maize: Origin, Domestication, and Its Role in the Development of Culture
perennial teosinte is the key missing link in the genealogy of both maize (Z.
mays) and annual teosinte (Z. mexicana). Modern maize and annual teosinte
both descend from the hybridization of perennial teosinte with a pod-popcorn.
Galinat (1985b: 247) believes that the condensed forms of teosinte, with
their triangular fruitcases and spikes borne in fascicles, may be an indirect product
of human selection. Starting with such a condensed teosinte, the transformation
into a botanically correct maize ear may have been simultaneously
attained in several places, and it began to spread in relatively rapid fashion, perhaps
in one hundred years.
There is no agreement as regards its genealogy. Doebley (1990: 13) believes
that the fact that teosinte is wild, and maize fully domesticated, leads to the conclusion
that the common ancestor also was a teosinte. Yet Grobman (2004: 436)
believes that Z. diploperennis could have crossed with wild maize (an annual diploid
plant) and thus given rise to a primitive annual teosinte, which would have
then acquired more maize-like characteristics after an introgression with maize.
Mangelsdorf (1974: 17ff., inter alia) suggests that teosinte is more specialized
than maize, at least as concerns four characteristics: adaptation to a limited
range of environments; the decrease in size from a polystichous cob (i.e., one
with many rows) to a dystichous one (i.e., a two-row cob); the decrease from
paired kernels to just one; and the hardening of the glumes and the rachis. 4 It
was for this reason that Mangelsdorf posited that maize is an ancestor and not
a descendant.
Goodman (1988: 208) points out that one can object that the genera related
with teosinte and maize are usually considered to be more similar to the former
than to the latter. This also does not take into account the great diversity in
chromosome knobs and isozyme alleles in teosinte, in comparison with Mexican
maize (Doebley et al., 1984, 1987; Kato-Yamakake, 1976; J. S. C. Smith et
al., 1982, 1984, 1985). Not only does teosinte have all of the knob positions
known in maize; it also has an additional number of them (mostly terminal
ones). Yet the origin and distribution of the chromosome knobs among maize,
teosinte, and Tripsacum, as well as their possible relatives, cannot be explained
satisfactorily except with the differentiation of populations instead of a single
originator plant that acted as a progenitor. Teosinte likewise seems to have had
isozymes from Mexican maize alleles, plus a few rare alleles that are restricted to
the vestigial populations of teosinte. Even so, there are numerous rare isozyme
alleles that appear in maize but not in teosinte (Doebley et al., 1984; J. S. C.
Smith et al., 1984, 1985).
Not all scholars have the same opinion as regards the morphological differences
or resemblances between maize and teosinte. Galinat (1977: 5) claims
that if one observes the floral characteristics that distinguish the maize cob
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De Wet and Harlan (1976) instead suggest that these characteristics indicate that maize is
quite specialized in both taxa.