From the Ancestry.com database description:
"The Family Data Collection - Births database was created while gathering genealogical data for use in the study of human genetics and disease. Compiling data for genetic research does not require the same type of documentation as traditional genealogical research. The genes themselves verify relationships and qualify or disqualify a person from a particular study. Citing the source of every genealogical fact in the electronic gene pool was deemed unnecessary and cost prohibitive by medical researchers. Millions of individual records were created from birth, marriage and death records; obituaries; probate records; books of remembrance; family histories; genealogies; family group sheets; pedigree charts; and other sources. The records collected that did not fit a specific study became the project's by-products and were schedule to be discarded. After viewing the quality of the source material used to create the gene pool and despite the absence of cited documentation, the electronic rights to the data were purchased, rather than see it destroyed.
After initially posting the Family Data Collection database in July of 2000, it was decided to divide the database into three separate collections of Births, Marriages and Deaths. By so doing it was possible to standardize place names and delete duplicates. This process also allowed us to add some additional records that were not included in the first launch of the database. This data covers the entire U.S. for a wide expanse of years. At a minimum, each record contains an individual's name, date and place of event, and the name of related parties."