Adding to the consensus of contemporary textbooks, is the testimony of older medical texts as well:

• Human Embryology, 3rd ed.
  Bradley M. Patten, (New York: McGraw Hill, 1968), 43.
  
  "It is the penetration of the ovum by a spermatozoan and resultant mingling of the nuclear material each brings to the union that constitues the culmination of the process of fertilization and marks the initiation of the life of a new individual."
  
  
• Biological Principles and Modern Practice of Obstetrics
  J.P. Greenhill and E.A. Friedman, (Philadelphia: W.B. Sanders, 1974), 17.
  
  "The zygote thus formed represents the beginning of a new life."
  
  
• Pathology of the Fetus and the Infant, 3d ed.
  E.L. Potter and J.M. Craig, (Chicago: Year Book Medical Publishers, 1975), vii.
  
  "Every time a sperm cell and ovum unite a new being is created which is alive and will continue to live unless its death is brought about by some specific condition."

In addition to the consistent testimony found in medical textbooks, there is some equally conclusive evidence that exists on the public record. In 1981, a United States Senate judiciary subcommittee received the following testimony from a collection of medical experts (Subcommittee on Separation of Powers to Senate Judiciary Committee S-158, Report, 97th Congress, 1st Session, 1981):

Professor Micheline Matthews-Roth
Harvard University Medical School

"It is incorrect to say that biological data cannot be decisive...It is scientifically correct to say that an individual human life begins at conception."

Dr. Alfred M. Bongioanni
Professor of Pediatrics and Obstetrics, University of Pennsylvania

"I have learned from my earliest medical education that human life begins at the time of conception."

Dr. Jerome LeJeune
Professor of Genetics, University of Descartes

"After fertilization has taken place a new human being has come into being. [It] is no longer a matter of taste or opinion...it is plain experimental evidence. Each individual has a very neat beginning, at conception."

Professor Hymie Gordon
Mayo Clinic

"By all the criteria of modern molecular biology, life is present from the moment of conception."

Dr. Watson A. Bowes
University of Colorado Medical School

"The beginning of a single human life is from a biological point of view a simple and straightforward matter – the beginning is conception."

The official Senate report reached this conclusion:

Physicians, biologists, and other scientists agree that conception marks the beginning of the life of a human being - a being that is alive and is a member of the human species. There is overwhelming agreement on this point in countless medical, biological, and scientific writings.