ILTIS, HUGH H. Department of Botany, University of Wisconsin, 430 Lincoln Drive, Madison, WI 53706. - Domestication of Zea: first for sugar, only then for grain? A novel idea with vast implications.
Logical assumptions that the maize ancestor, Balsas Teosinte Zea
mays ssp. parviglumis, was first domesticated for grain
need re-examination, for teosinte grains, each permanently imprisoned
in a hard CUPULATE FRUIT CASE (CFC), are not accessible for palatable
food. Though CFC's are abundant, easy to harvest, store and
indestructible, why are they unknown from the older archeology? And
how could the key teosinte mutation (Tga 1), opening the CFC's and
making grains accessible for use, ever been discovered in the wild --
one so astronomically rare that George Beadle (1971-1973), by
visually inspecting some 4 million CFC's in over 40 days, could not
find a single one? Must we not assume then a fortuitous, face-to-face
discovery by some sharp-eyed horticulturist among plants already
semi-domesticated: for sugary pith (alcohol?), green crisp ears,
roasted ear clusters, trellises for beans. Must we then not also
assume only one mutant, a maizoid "Eve", its naked grains
soon protected from predation and, by backcrossing to its semi-wild
neighbors, escaping this narrowest of narrow "domestication
bottleneck" some 7,000 years ago? Lastly, "unbranched"
maizoid phenotypes are automatic density-dependent responses to
competition, with primary branches telescoped into subtending
leafsheaths, leading to larger ear clusters and ready-made husk
systems. With mutated CFC's now "open", human selection of
grains commenced, loss of abscission layers and reactivation of
suppressed spikelets soon followed, and the sequential maturation
arrangement of the ears and competition between ear clusters made the
cascade of ever-increasing apical dominance by ever-fewer ears
virtually inevitable. As for theories to sexually transmute teosinte
tassel spikes into their maize ear homeologs, they are unnecessary
explanations of common phenotypic variability, this was well
understood but its implications totally missed by this author (See
Iltis, in Soderstrom et al. 1987: fig. 1). To quote Mark Twain,
"The eye cannot comprehend when the imagination is out of
focus."
Key words: corn evolution, Economic Botany luncheon talk, maize domestication