The sperm is a living thing. The egg is a living thing. When two living things come into contact, you guessed it, it forms a living thing. When the egg starts to divide, it starts to form a new life. A new HUMAN life. This is all at the point of conception. Therefore, human life begins at conception.
We recognize sperm and egg cells as LIVING things. Separate components, certainly, but living nonetheless. Each one contains approximately half of the DNA necessary to create a human being. Now, does the conjoining of the two cells change the nature of the life within them? I believe it would be ludicrous to such a thing. The fundamental difference is the complete set of DNA within the newly created zygote. Some people would argue that this is nothing but a mere clump of cells, to which I reply that essentially, that is what we ALL are. Obviously, we have different stages of development throughout our lives. At this particular stage in question we are unable to have any real thought or any real desire. Some would suggest that his means that person hood does not exist and therefore it is acceptable to disregard this life as non-human. By that definition however, any elderly person with severe Dementia or Alzheimer's would not be considered a person, and could technically be disposed of legally and with moral justification. Obviously, a reasonable mind would find such a thing abhorrent. To separate person hood from any point in our development is to call into question the worth of an individual who is less developed than another, no matter how slight that difference. If a pregnant woman is murdered, the murderer will be charged with TWO murders, regardless of the stage of pregnancy. This would suggest to me that more than just morally, but legally, an unborn human HAS human rights. I rest.
It is basic biology that a human life starts at conception. The zygote works like any other human cell, and the fetus is constantly dividing cells. Not to mention the fetus/zygote is composed of a different DNA set than the mother, and it has different blood. Life obviously begins at conception, and abortion is the killing of a human being!
As an embryo, we are basically a jumble of cells that are replicating until we are ready to be born. A cell is not only a building block in life, but a living thing. Fetuses have hearts and organs just like we do, they are just incapable of living on their own. They are attached to the mother in order to survive. Just because they are dependent on the mother doesn't mean that they aren't a human or just "a part of a female's body". These fetuses will grow into human beings and they already have the makings of one.
It's very simple, actually. If you have 46 chromosomes (or sometimes 45 or 47 due to genetic mutations) then you are a human being. If you had 48 chromosomes, you wouldn't be a human, you would be a chimp. Since having 46 chromosomes (or 45 or 47) begins at conception, human life begins at conception.
Why would you believe human life begins at conception?
As far as I know, life on earth began about roughly 4 billion years ago, then 2-3 million years ago the first humans evolved, "homo habilis" and "homo rudolfensis". The first "homo sapiens" evolved about 200.000 - 100.000 years ago. As you see, human life has began long ago, so I wouldn't say it begins with conception.
Also the egg cell and the sperm are both made out of living cells, so again, there is already life before the moment of conception. Now, is this life also human? Well, what is human, exactly? If we want do define something as human, we have to take a look at what separates it from all the non-human beings out there, right? So let's see. Humans can think complex thoughts, what other animals probably can not. We understand that other beings might have more knowledge and know things we might don't know. A concept, that, so far hasn't been observed in other animals ( at least as far as I know). Well that is all that comes to my mind so far, besides the small physiological and biological differences.
Now let's see, are these two qualities already present in a fetus shortly after conception? I think not. In fact test have shown, that kids under the age of three seem to "think" a lot like other animals. Now I don't know the exact age ( and I am too lazy to look it up) but I know that test also have shown, that small children don't understand the concept, that other beings might know things that they don't know. Now that raises the question, if they are still human? Well from a biological standpoint they are. But from a philosophical perspective they probably aren't. I am not saying, that I am seeing children as "lesser beings" or something.
But I definitely wouldn't say that human life begins at conception. That would be like saying, that a single apple seed is already an orchard.
This question is a poor attempt to imply that embryos are people with rights, when clearly biology shows that they have none of the signifiers of personhood. Embryos and fetuses of abortable gestation age (under viability, in the United States) do not have the ability for sentience, consciousness, or to feel pain- all of which are hallmarks of personhood.
Humans are living, breathing, non dependant, meaning they don't depend on another organism or human for vitals. Fetus's are simply groups of cells attached to another human. Since it's physically attached it can just be considered part of a female humans body. Also, notice how we refer to them as a fetus. NOT a human.
As stated by other posters, it is easy to get confused when using terms such as the beginning of human life. If we take this to mean the point at which the embryo gains sentience and thus becomes a conscious being, this does not happen at conception but rather at around 12 weeks into pregnancy, when brain activity begins. Before this point any semblance of what makes us human would be impossible in the embryo.
I'll assume that you're saying "human life" where you mean to say "personhood". And personhood definitely does not begin at conception. Personhood (minimally) requires a developed nervous system; an entity must have a degree of consciousness, the ability to perceive stimulus from the outside world, a demonstrable distinction between "self" and "other", the capacity to think and to feel, or it is not a person.
An embryo, at the moment of conception, possesses exactly none of those things, and is therefore not a person. There's room for debate (and more appropriately, scientific research) in terms of exactly when a developing fetus acquires these traits, but it is definitely not at the moment of conception.
There's little sense in debating when "human life" begins, because human life does not have any sort of protected legal status in and of itself. The law applies to persons, and thus personhood is the relevant subject to debate.
I can scrape some excess skin off of a callous, and for a time those skin cells will remain alive and are 100% human. They may even be counted as "human life" by some technical application of the term. But they certainly are not a person. So it goes with an embryo at the moment of conception. It's alive, it has human DNA, but it is not a person and is not entitled to the same legal consideration as a person. Let's not confuse the issue by conflating "human life" with "personhood".
A fetus is a parasite, and therefore alive in the same way that ticks and viruses are alive. When it is born, it is an independent human. To say that human life does begin at conception is to say that there are single-celled humans, and to say that people with dead brains are alive.