DISCLAIMER: This blog post is meant
for biological definition purposes. It is not meant to establish or argue any
moral or philosophical points.
Fertilization – the fusion of gametes to produce a new organism – is the culmination of a multitude of intricately regulated cellular processes. [Marcello et al., Fertilization,
ADV. EXP. BIOL. 757:321 (2013)]
organism for decades:
organisms.”[Keith L. Moore & T.V.N. Persaud Before We Are Born –
Essentials of Embryology and Birth Defects (W.B. Saunders Company, 1998. Fifth
edition.) Page 500]
the developing organism from the time of fertilization until
significant differentiation has occurred, when the organism becomes
known as a fetus.“[Cloning Human Beings. Report and
Recommendations of the National Bioethics Advisory Commission. Rockville, MD:
GPO, 1997, Appendix-2.]
critical landmark because, under ordinary circumstances, a new,
genetically distinct human organism is thereby formed.“[O’Rahilly, Ronan and Muller,
Fabiola. Human Embryology & Teratology. 2nd edition. New York:
Wiley-Liss, 1996, pp. 8, 29.]
with fertilization, a process by which the spermatozoon from
the male and the oocyte from the female unite to give rise
to a new organism, the zygote.“[Sadler,
T.W. Langman’s Medical Embryology. 7th edition. Baltimore: Williams &
Wilkins 1995, p. 3]
zygote is in some nebulous “in between phase” – not a gamete but not a human
organism. But biologically, life cycles do not contain such a phase. In humans
(animals), our life
cycle goes from diploid organism, which produces haploid gametes,
which combine to form a new diploid organism. The zygote isn’t in an unknown
stage; it’s the same organism as the grown adult, but at an earlier stage of
some species, and the human ZEF is part of the human species (Homo sapiens) by
virtue of its human DNA.
(2) An individual belonging to a
group of organisms (or the entire group itself) having common characteristics
and (usually) are capable of mating with one another to produce fertile
mating” does not mean at any given instant. For example, newborns are not
capable of mating, but are still organisms of the human species. “Capable
of mating” refers to an organism who should be capable of mating in their
lifetime, barring sterility. And on that note, also keep in mind that there’s a
difference between an individual organism being sterile vs. an organism having
developed genetic changes which render reproduction with his origin species
species. There are no “non-species” organisms. The organism is part
of its parents’ species. For example, two honey-badgers cannot reproduce and
create a frog; their offspring would also be a honey-badger. Furthermore, an
organism can never change its species mid-development (in the middle of its
life). A honey-badger zygote develops into a honey-badger adult; a honey-badger
zygote can’t develop into a frog adult.
another species over many generations.
This is called speciation. Speciation most often occurs when one species is
split into two or more geographical groups (allopatric speciation). Genetic
changes accumulate over many generations, not within a single lifespan, such
that if the groups ever met again, they would not be able to produce viable
offspring. That’s when you can say “these are now two
offspring is an organism but has no species membership.”
because their parents are human and because they have human DNA. They are not
part of some other species, nor do they lack species membership.
of the species Homo sapiens is a human being.
definitions of human being, including “a person, especially as distinguished from
other animals or as representing the human species.” I am only referring to the
biological definition of human being when I
use the term:
1. any individual of the genus
Homo, especially a member of the species Homo sapiens.
the zygote is an organism and a member of the species Homo sapiens, it is a
human organism and therefore biologically a human being.
Below we present some topics that have been brought up as questions or
single organism composed of more than one unique DNA type (or antigenic marker
on red blood cells). In animals, this can result from the merging of 2+ zygotes into
one entity (tetragametic), or from twins sharing blood supply in gestation
(“blood chimeras” have more than one blood type). You can be a microchimera if
you received blood from mom early in gestation, if as a mother you received
fetal cells during pregnancy (as most do), or
just from a blood transfusion. You’re even considered a chimera if you received
an organ transplant. Chimerism is usually asymptomatic, but rarely it can
result in things like intersexuality if
it results from absorption of a twin.
a chimera is still one individual human organism. From the britannica article:
an organism or tissue that contains at least two
different sets of In dispermic
chimeras, two eggs that have been fertilized by two fuse together, producing a
so-called tetragametic individual—an
individual originating from four , or sex cells.When two zygotes do not undergo fusion but
exchange cells and genetic material during development, two
individuals, or twin chimeras, one or both of whom
contain two genetically distinct cell populations, are produced.
realize it. You may have multiple DNA types due to absorption of some cell
types or an entire other organism — and this doesn’t change the fact that you
are still an individual human organism.
objection is because people sometimes think of DNA as some sort of marker of
individuality, and therefore they may see multiple markers of DNA as a sign of
“multiple individuals.” DNA can function as an
individuality marker, but it doesn’t always as is evident in the case of
identical twins. DNA is simply a code of instructions for the body to function
effectively as an organism. That’s it. If it is unique to you, and you only
have one set of DNA — great! If you do not have unique DNA, or you have
multiple unique DNA sets — you’re still a singular human organism.
something like: A zygote can twin, therefore how can you say it’s an individual
human being before the potential twinning stage is over?
because by extension, none of us are individual human beings. Why? Well
twinning is essentially the same
thing as cloning. The main difference is that one happens
“naturally” and the other happens artificially. The point is, if your
DNA can be taken from an epithelial cell on your arm and made into a clone,
would spawning a clone mean you were not an individual human being to begin
with? With advanced technology, we could all conceivably be in the
“twinning” (cloning) phase indefinitely! Yet we’re all still singular
version of chimerism, by the way. Absorbing or spawning organisms
does not change the fact that a single organism is still a single
Read more: Monozygotic twinning, Weasley brothers, flatworms, and cow clones.
Q3. In Vitro Fertilization (IVF)
means “outside the body.” IVF is when we use sperm to fertilize an
egg in a laboratory dish instead of a uterine tube (in vivo). The
resulting embryo is then placed into the woman’s uterus to allow implantation
and thus a pregnancy, which is why IVF is considered a type of assisted
reproductive technology (ART).
that — due to time, cost, and failure rates — companies performing the
procedure will always fertilize more than one embryo at a time. Many will then select
the highest quality embryos
to increase chances of a successful pregnancy. This means either
cryopreservation (freezing) of the remaining embryos if the couple wants to pay
for it, or destroying them.
US, multiple embryos can be transferred to the woman’s uterus to increase
chances of a successful pregnancy. This can sometimes result in multiple
implantations (twins or more), but this isn’t usually the case, which means the
other embryo will have been miscarried.
survival rates for IVF are poor, nothing about IVF alters the basic biological
process outlined above: gametes join to form a new human organism. It is merely
accomplished in a laboratory rather than in the womb. People conceived through
IVF are as human as anyone else.
nothing inherently wrong with IVF if it were done on one embryo at a time,
which gives every embryo the best possible chance of life. But this is not standard practice.
Rather, IVF is used to make multiple embryos with the foreknowledge that not
all will be allowed to grow and live their life, and in most cases with the
foreknowledge that some will die.
conceptions die before ever implanting, or soon after. Why is that foreknowledge
ok in natural conception, but suddenly wrong if done in a petri dish?
trying their best to give every zygote a chance to live. If a zygote dies
naturally, that is not the preemptive work of the couple creating him/her as it
is in most cases of IVF.
men and women who have fertility problems but have a great desire to create
their own offspring, the solution is not to treat human organisms as disposable.
Q4. Random Mutations
replenishes cells via mitosis. Every time a cell is copied, the replication
machinery — while mostly very accurate — will make mistakes in copying the
template DNA. Not to worry, there is proofreading machinery too. However, even this can
make mistakes. So in the end, there is some non-zero
number of mutations that are
incorporated into the new cell which are propagated in that cell line (although
you still have your original batch of stem cells).
older, some portion of your cells will have a specific DNA sequence that is
different than the one you had when you were younger. Some people see DNA as a
unique identifier, like a name, and therefore a change in this identifier might
mean you are not the same individual.
the same person I was when I was 5; I have different memories, experiences,
mindsets, functionality, and slightly different DNA. But guess what? I’m
still the same organism.
While some people may ascribe to the belief that we are not the same
“person” we were yesterday, in a scientific sense we are still the
same organism. An organism goes through changes in its life, but it doesn’t end
its life and begin a new one in the same body.
Q5. Life as a Continuum vs Individual Life
We have written
about this topic before. The objection goes something like: “Human life doesn’t begin at fertilization; it began millions of years
The objection confuses the life of an individual human
organism with life arising from life (also known as the Law of
Biogenesis.) The Law of Biogenesis points out that living matter has to
come from other living matter. However you, as an organism, were not the
precursor molecules that eventually formed you, as an organism. For example you
were not sperm and egg. Or an early primate. The precursors that create an
organism are not equivalent to the organism itself.
preexisting life does not change the fact that an individual organism’s life
has a start and end point. And for human organisms, that starting point is
always as a zygote.
Q6. Hydatidiform Mole
pregnancies in the US) is an abnormal fertilized egg which implants in the
abnormality can occur when one (90%) or even two (10%) sperm combine with
an ovum that has no maternal
DNA; the sperm then replicates its DNA to create an artificially
“diploid” cell. This results in a mass of abnormal tissue which can
develop into cancer (15-20%) and/or invade the uterine wall (10-15% of all
molar pregnancies will invade if not removed). Complete moles have no embryonic growth; there is only abnormal placental tissue. Maureen Condic said it much better than I ever could (the bolded part is most important):
Despite an initial (superficial) similarity to embryos, hydatidiform moles do not start out as embryos and later transform into tumors, they are intrinsically tumors from their initiation. Moreover, they are not frustrated embryos that are “trying” (yet unable) to develop normally. Just as a CD recording of “Twinkle, twinkle little star” is not somehow thwarted in its attempt to play the “Alphabet song” by a deficiency of notes in the fourth measure …, hydatidiform moles are not “blocked” from proceeding along an embryonic path of development by a lack of maternally-imprinted DNA. Rather, hydatidiform moles are manifesting their own inherent properties—the properties of a tumor. Even in the optimal environment for embryonic development (the uterus), hydatidiform moles produce disordered growths, indicating they are not limited by environment, but rather by their own intrinsic nature; a nature that does not rise to the level of an organism…If the necessary structures (molecules, genes etc.) required for development (i.e., an organismal level of organization) do not exist in an entity from the beginning, the entity is intrinsically incapable of being an organism and is therefore not a human being. Such entities are undergoing a cellular process that is fundamentally different from human development and are not human embryos.
mole on the other hand is when a normal
ovum is fertilized by two
sperm or by one sperm that replicates itself, creating a triploidy or
tetraploidy cell. In this case, an embryo/fetus can develop. Rarely is this embryo viable; partial moles usually miscarry and even when they do not the embryo is often overtaken and destroyed by the abnormal placental tissue. However there have been extraordinarily rare cases of triploid human organisms surviving until infancy. These are human organisms with severe and fatal genetic abnormalities.
example to argue that fertilization is not necessarily the beginning of a human
being, or that because fertilization can result in these moles, then it’s wrong
to say a fertilized egg is a human being.
fertilizations result in human beings. Clearly, some result in complete moles.
Fertilization is a necessary
but not sufficient condition
for the formation of a human organism.
organism (human being). The exception really does prove the rule. As the
previous blog post pointed out, pro-lifers tend to take shortcuts here and say
that fertilization is the beginning of a new human life. Most of the time,
that’s true. Perhaps it would be better to just say “a zygote is a human
being,” or something similar.
Read more: Hydatidiform moles and molar pregnancies
of pregnancies (post-implantation) will miscarry.
may cite the high number of miscarriages to imply that abortion is not morally
problematic or the zygote is not a human being.
intentional killing. Every human being will die. Some die of cancer (natural
death) and some die of gunshot wound (intentional killing). If lots of people
die of cancer, would that make shooting them morally acceptable? No. Just
because people die naturally, whether in old age or pre-implantation, doesn’t
mean it’s acceptable to kill them, whether by gun or by chemical.
were not human beings to begin with? Clearly not. Likewise a high rate of
natural death in the preborn does not mean they were not human beings. As
stated above, a zygote is a human being, whether it dies
naturally in a day or in 100 years.
may also cite the high number of miscarriages to question why pro-lifers don’t
appear as concerned with the high number of deaths there.
Why do people speak out
more passionately and perhaps more frequently about shootings than they do
about cancer? Does it mean that people who die naturally, from cancer, don’t
matter? Does it imply that they don’t really care
about people dying in general? Of course not. It makes sense to be more upset
by a human being intentionally killing another human being than it does to be
upset by a natural cause of death. Furthermore, stopping this type of killing
is more likely within our grasp than finding a cure to cancer.
intentional killing of young human beings than we are equipped to stop natural
miscarriages. And it’s understandable that an egregious harm being perpetrated
by an intelligent human being (capable of moral contemplation) is more
upsetting than harm perpetrated by non-moral agents.
Read more: Nearly half of all fertilized eggs fail to implant.
my arm? Sperm are also human, is masturbation murder?
This objection conflates “human” the adjective and “human” the noun. Epithelial cells and sperm are human cells, but they are not human organisms. There is a
difference between components that make up an organism (epithelial,
endothelial, renal, pulmonary, hepatic cells, etc) and the organism itself.
Human organisms (human beings) are what pro-lifers are concerned with, which includes