I think this is an important and complex issue.
It would be helpful to discuss the vinaya and sutta references in Ajahn Brahm's article that I referenced here:
http://www.dhammawheel.com/viewtopic.ph ... ead#unread
mikenz66 wrote: http://www.dhammatalks.net/
When Does Human Life Begin?
http://www.dhammatalks.net/Books7/Ajahn ... _Begin.pdf
1. What Did the Buddha Say?
1a. “(Human life begins) when in the mother’s womb, the first citta
(‘mind’ or ‘thought’) arises, when the first consciousness
manifests”.1
1b. “Bhikkhus, the descent of the gabbha (misleadingly translated
as embryo by Bhikkhu Bodhi) takes place through the union of
3 things – the union of mother and father, the mother is in
season, and the gandhabba (stream of consciousness) is
present.”2
1c. “If viññāṇa (consciousness) were not to descend into the
mother’s womb, would nāma-rūpa take shape in the womb?
Certainly not, Venerable Sir.”3
Nāma-rūpa = feeling (vedana) perception (saññā) contact
(phasso) will (cetanā) attention (manasikāro) and material
form (rūpa ).
1d. Nāma-rūpa and consciousness are like two sheaves of reeds
standing leaning against each other. If one were to remove one
of those sheaves of reeds, the other would fall. So, with the
cessation of nāma-rūpa comes cessation of consciousness, and
with the cessation of consciousness comes the cessation of
nāma-rūpa. 4
Notes
1 From Pārājika 3, the rule about deliberately killing a human being, repeated at Vinaya Mahāvagga 1.75.
2 From Ven. Bhikkhu Bodhi’s translation of Sutta #38 of the Majjhima Nikāya..
3 Mahānidāna Sutta, DN15.
4 Abridged from Nidana Saṃyutta No. 67.
There are another three sections...2. What Did the Buddha Mean?
2a. Human life begins when the stream of consciousness (s.o.c.)
enters the embryo-fetus and the first consciousness manifests
therein.
2b. Such an arising of consciousness is caused by the combination
of 3 conditions: parental union, fertility and an s.o.c. being
available.
2c. The above causal link is not necessarily instantaneous.
Buddhist causality includes results that appear a long time
after their cause. A prime example is “when there is birth,
there is old age, sickness and death.” It is a mistake to assume
that the s.o.c. descends into the mother’s womb at the very
moment of parental union. Such a belief would beg the
question into what does the s.o.c. descend? Into the lucky one
of the millions of sperm, or into an egg that might well remain
unfertilized? The Buddha meant that some time after
parental union, with the other two factors also being fulfilled,
there is descent of the s.o.c. into the mother’s womb.
2d. Point 1d, above, shows that there cannot be consciousness
without feeling + perception + contact + will + attention +
material form (nāma-rūpa). When one manifests, so does the
other, immediately.
Mike