ECOL3453 - Crop Ecology

Semester 2  2004-20005

Lecture 4 - Origins of Agriculture and Crop Plants 3

Selection, natural and human

In the evolution of crop plants we can usefully distinguish, in principle though not always in practice, between natural and human selection. The former is selection (i.e. differential reproduction that may, but will commonly not, be expressed as zygote mortality) inherent in the cultivation of a genetically heterogeneous population at a particular place and time. The latter is the result of conscious decision by the farmer, or plant breeder, to keep the progeny of a parent in preference to others. In either case, there will tend to be evolutionary change in the form of improved adaptation, that is enhanced reproductive fitness. The relative importance of natural and human selection has changed over time in favour of the latter. That there was some conscious selection in the earliest stages and that natural selection in the modern plant breeder's plots is still significant seems equally certain.

Some characteristics are obviously the result of human selection:

• Reduced spininess
• Reduction of toxic constituents
• Development of attractive colours and colour patterns
• Multiple uses of the same species

Others the result of natural selection:

• Pest and disease resistance
• Altered photoperiod and vernalization requirements associated with latitudinal and climatic adaptation
• Non-shattering infructescences and fruits
• Reduced seed or tuber dormancy

Others the result of a combination of human and natural selection:

• Reduced plant size
• Determinate gowth
• Shorter life cycle

Compile a table of examples of crops grown in the Caribbean that exhibit the above traits.