Abortion is a controversial subject. The key question in the abortion debate for a libertarian is the following: When does a rights-bearing human emerge? The answer to this question is crucial because a non-rights-bearing human, by definition, has no rights and, therefore, can be justifiably killed. However, a rights-bearing human, by definition, has rights and, therefore, cannot be justifiably killed (except in self-defense); in fact, an unjustified killer of a rights-bearing human is, as logically explained by the interrogator Ivanov in Arthur Koestler’s Darkness at Noon,

“a slaughterer”.

What are the possible moments in time when a rights-bearing human emerges (i.e. when personhood begins)? A plethora of points in time have been adopted by various societies. The most common selections have been the following:

1. Pre-fertilization views assert personhood exists in human eggs, human sperm, or human embryonic and induced pluripotent stem cells.
2. Fertilization views assert that personhood emerges at ejaculation, fertilization (sperm entering egg), or fusion of genetic material into a new set of chromosomes.
3. An embryological view asserts that personhood emerges after gastrulation (approximately 12 days post-fertilization when monozygotic twinning is no longer possible).
4. Neurologic views assert that personhood emerges at 8 weeks post-fertilization when organogenesis has been completed and a rudimentary nervous system exists, at 20 weeks post-fertilization when thalamus (a brain structure crucial for nervous system integration) development has been completed, at 24-25 weeks post-fertilization when a functionally mature brain (evidenced via bilaterally synchronous brain EEG activity as reported per K.J.S. Anand and P.R. Hickey in their frequently-cited November 1987 New England Journal of Medicine paper entitled “Pain and its Effects in the Human Neonate and Fetus”) develops, or when the human child first employs reason (at some time in childhood).
5. An ecological view asserts that personhood emerges when a fetus can exist separately (fetal viability) from the uterus (approximately 22 weeks post-fertilization).

I claim that the optimal choice for libertarians (based on the current state of medical science) is the third version of the neurologic view (a rights-bearing human emerges at 24-25 weeks post-fertilization when a functionally mature brain develops, otherwise referred to hereafter as “brain birth”). Why? I assert the following three reasons:

1. A coherence/symmetry argument: Because death of a rights-bearing human is scientifically defined at brain death, birth of a rights-bearing human should be scientifically defined at “brain birth”.
2. A praxeological argument: Because the fundamental difference between a rights-bearing being and a non-rights bearing being is the capacity to reason (required for human action), the emergence of a rights-bearing human should be defined as no earlier than the moment in time when a human develops the minimum mental equipment necessary to exhibit reason, which occurs at “brain birth”.
3. An ethical argument: Because humans do not specifically employ reason at “brain birth” or continuously throughout life (which if required for rights-bearing humans would justify the killing of all humans at various times throughout life), the emergence of a rights-bearing human should be defined as no later than the moment in time when a human develops the minimum mental equipment necessary to exhibit reason, which occurs at “brain birth”.

Ultimately, what are the implications for abortion if libertarians adopt the “brain birth” version of the neurologic view? First, abortion would be justified (not an act of aggression and, therefore, not a crime) from fertilization until the end of the 23rd week of fetal life. Second, abortion would be unjustified (an act of aggression and, therefore, a crime) from the beginning of the 24th week of fetal life through birth. Third, if an unsuspecting female unwilling to be a child’s guardian discovered she was pregnant OR significant medical complications occurred 24-weeks post-fertilization or later, she could justifiably “evict” (a modified version of Professor Walter Block’s evictionism theory) the fetus via surgical delivery by relevant medical professionals, at which time the fetus would be treated in a neonatal ICU and guardianship would be transferred, as needed, to willing guardian(s). Finally, in the rare, horrific scenario of a life-threatening pregnancy complication 24 weeks post-fertilization or later, if the fetus cannot be surgically “evicted” without death of the mother, the mother could justifiably proceed with an abortion as a matter of self-defense.