Definition of "introgression" [in•tro•gres•sion]

• Infiltration of the genes of one species into the gene pool of another through repeated backcrossing of an interspecific hybrid with one of its parents. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The result was an "introgression" of Neanderthal alleles into the human lineage."
• "Whatever that allele does, it must have conveyed a very strong evolutionary advantage, because from that single event of what geneticists politely call "introgression" it spread to 70 percent of the human population today."
• "So it's still "far out," Harpending admits, but civilization could have gotten its start in an act of "introgression" with another species."