An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Haig D.Haig D.Proc Natl Acad Sci U S A. 1996 Jun 25;93(13):6547-51. doi: 10.1073/pnas.93.13.6547.Proc Natl Acad Sci U S A. 1996.PMID: 8692853Free PMC article.
Haig D.Haig D.Philos Trans R Soc Lond B Biol Sci. 2015 Jul 19;370(1673):20140178. doi: 10.1098/rstb.2014.0178.Philos Trans R Soc Lond B Biol Sci. 2015.PMID: 26056362Free PMC article.Review.