The history of Maize domestication

A Brief Prehistory of MexicoTime before the present b.p.

Mirambell (2000)

Zeitlin y Zeitlin (2000)

4,000 - Neolítico Formative

5,000 - 4,000 Protoneolítico Late Archaic

7,000 - 5,000 Protoneolítico Middle Archaic

12,000 - 7,000 Cenolítico superior

Early Archaic

35,000-12,000 Cenolítico inferior Late Paleo-Indian

? to 35,000 Arqueolítico Early Paleo-Indian

2,000

Early microfossil evidence for

maize in archaeological

contexts.

Sites of the Protoneolithic period

Archaeological context of the Protoneolithic

Period(1)

Archaeological context of the Protoneolithic

Period(2)

Figures from Ranere et al, 2009

Morphological Characters studied on archaeological maize

1. Specimen Condition

2. Specimen Length

3. Cob Diameter

4. Rachis Diameter*

5. Pith Diameter*

6. Row Number*

7. Cupule Width*

8. Cupule Depth

9. Rachid Length** Show significant variation over

time

San MarcosCoxcatlanEl Riego

Calculating evolutionary rates

• Calculation of rates of change follows Haldane (1949):

Darwin = ln(x2) - ln(x1) / t

Where ln is the logarithm base e, x1 and x2 are the later and earlier average specimen dimension and t is the length of time separating the two specimens.

San Marcos Coxcatlan El Riego

Evolutionary rates in Wheat (after Tano and Willcox 2006)

Postulated allele frequencies of indehiscent (d) and dehiscent (D) over 10000 + radiocarbon years of Middle Eastern prehistory (left) and relative fitness of geno-types of wild wheat. While selection for indehiscent phenotypes appears to haveOccurred gradually, selection is not continuously increasing. This is similar tothe puntuated pace of evolutionary change in maize in Mesoamerica

Conclusions• The antiquity of human manipulation of maize is suggested

by maize and teosinte microfossils in some areas of the Americas, this evidence does not yet indicate the impact of human selection on maize.

• Contemporaneous Protoneolithic sites in Mesoamerica are discordant about time and place of domestication.

• Study of inflorescence morphology shows the intensity of human selection on maize is greatest around the 5 th millenium BP cal.

• Human selection intensity on maize is not continuous, in a similar way to that of the Middle East where local effects – environmental variation between and within sites over time – affect the cultivator’s ability to monitor and act on the effects of selection.