Current evidence for the domestication of soybeans puts this event in China about 5,000 years ago. Domestication is a process of selective breeding initiated by humans to "improve" wild plants and animals so they have more desirable characteristics. While this process may make a plant or animal more useful to humans, farmers and biologists worry about inadvertently ending up with a plant or animal that we depend on that can't respond to new disease organisms, climate change or to the old disease organisms when we raise plants and animals in new places.
Populations of plants and animals depend on genetic diversity as a method of responding to unusual events, and for self-improvement. If all of the plants in one field are genetic clones of each other and they encounter a new destructive pest, the entire field of plants may be lost. This is bad for farmers and bad for the plants (and animals). Genetic variation is nature's way to trying out new combinations of genes, some of which may be harmful and quickly disappear after several generations while others provide benefits to the organism and may increase in frequency over many generations (and some may be a bit more helpful than harmful). Rare alleles in a population may confer characteristics that allow a few percent of the population to survive an adverse event.
To determine just how diverse domesticated soybeans are in the USA (47% of world production), and perhaps assess the risk of our current plants being unable to respond to new challenges, the authors of this paper sequenced 111 DNA fragments from 102 soybean genes. They examined 25 diverse cultivars developed in the 1980's, 17 Asian cultivars that were the stock for soybean introduction in the USA last century, 52 diverse Asian descended lines and 26 diverse G. soja lines.
Bucking the common wisdom of the day, they found modern soybean cultivars grown in the USA have retained 72% of the sequence diversity that is found in related stocks of this plant in Asia, but, as might be expected from selective breeding, the American lines have also lost 79% of the rare alleles.
The authors offer the explanation: ancestral G. soja from which modern lines of plants in the USA descend was itself unusual and had very low diversity to begin with. The authors suggest that high priority be given to searching out lines that have the rare alleles, as these may be a genetic source for future "improvement" of the specie.
Reference: Impacts of genetic bottlenecks on soybean genome diversity, Hyten et al., Proceedings of the National Academy of Sciences, USA 103(45): 16666 - 16671; published on line 26 Oct 2006 (open access)
Tom D. Dillehay et al. report new analyzes of ancient hearth remains from the Monte Verde site in modern-day Chile, which indicate human presence at that site as early as 14,220 years B.P. The analysis indicates the people of the area exploited several different ecosystems: ocean-beach, river delta and inland locations. In the same issue of Science is a paper by M. Thomas P. Gilbert et al. that reports on the recovery and sequencing of ancient human mtDNA from coprolites (feces) in Oregon in the Northwest of the United States. They found mtDNA haplogroups A2 and B2. Their dating of the human samples is at least 1,000 years older than the Clovis toolkit dates.
