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Children of the Corn: A Reader Objects


A correspondent notes Jay Richards’s observation the other day here at ENV:

In fact, based on the empirical evidence, I’m deeply skeptical that any series of genetic mutations alone, even if they are guided, can produce anything profoundly new (such as a new animal form or body plan).

Our attentive reader poses a challenge from corn:

Check on the evolution of teosinte into modern corn (maize). Since humans speeded things up by planting only the best kernels, it happened in a short time AND it happened recently enough so that we have sample kernels from the intermediate stages, complete with intact DNA. Teosinte still grows wild, so we have that too.
It appears to have taken only a dozen or so mutations to convert what looks for all the world like grass with tiny tooth shatteringly hard seeds into modern corn plants with their enormous cobbs loaded with large, soft kernels.
Here’s a good article on the transitions. Look at the second picture there to see a teosinte seed compared to a corn cob. A BIG difference in form and body plan! Here’s a picture of teosinte.

Good query — glad you asked. So what’s up with that, anyway?
Obviously we’re dealing with “guided evolution” here, as the reader recognizes. The evidence for the domestication of corn from teosinte is pretty good; much of the relevant work has been done by the Doebley lab at the University of Wisconsin. Pioneering work was done by the geneticist Hugh Iltis, also at Wisconsin. The Doebley group is particularly interested in changes in plant morphology (we don’t recall ever seeing the term “body plan” used for plants).
We would not consider this to be an example of the origin of a new body plan, however. Not even close. Teosinte and maize (domesticated corn) cross normally within the genus Zea, producing fertile hybrids (cf. dogs, wolves, and coyotes, inter-fertile within the genus Canis).
More to the point, the evolutionary biologists who work on animal body plan origin and evolution do not consider teosinte-to-maize a useful model for their unsolved problem, mainly because teosinte — if we take it as the ancestral group out of which corn was domesticated — already possessed the genetic “raw materials” that would later enable humans to domesticate the wild plant into a useful crop. As John Doebley put the point in 2004, “The critical genetic variants involved in maize evolution were pre-existing in teosinte populations” (p. 46).
“Grant me Zea, and I’ll evolve you corn” is a whole lot like Darwin saying, “Grant me a mudfish…” for the origin of Vertebrata. Yes, he actually did say that.
Photo credit: Japonica Striped Maize, Wikicommons.

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