Hogs may shed light on human growth.

It is common wisdom and accepted scientific thinking that today's generation of people is taller because of improved nutrition the 20th century. However, it may be that, by lessening the effects of chronic disease, vaccines play as important a part as nutrients, hypothesizes Allan Schinckel, an animal scientist at Purdue University, West Lafayette, Ind.

Research conducted on hog growth has found that chronic disease can slow the rate of growth by as much as 40 to 60%. Schinckel theorizes that it causes a genetic shift, which makes the animals divert resources from growth to fighting disease.

"This genetic shift may be due to changes in gene transcription and gene expression." he suggests."It may be that if the body is chronically fighting disease. that at some point it doesn't make RNA for a certain gene; that it activates a genetic switch and goes into a survival mode where it puts energy into fighting disease instead of into growth." RNA is the biochemical messenger that tells cells to produce new...