When does life begin?

Answer 1

The beginning of "a life" is a matter of moral, biological and legal interpretation.

The range of moral views on when a life begins is far to broad to adequately address here.

Biologically an entity has a number of qualities identified with life. Though no fixed rule exists, it is not controversial to include,
1) respiration, i.e. energy intake and metabolism and
2) reproduction and some form of replication.

If one takes the biological is the definition of Life, then all cells of all plants and animals and bacteria and fungi are alive. If a living entity is further identifiable as a separate entity biologically able to mature into a separate life form, then biologically one may say it is "a life."

For humans, the starting point for discussion of "life" is then typically taken as the time of inception. The point of inception is the point that the sperm and egg combine and DNA material from the two coincide in one cell.

If DNA is combined through the natural process of reproduction, the point of inception is well defined, whether it is interpreted as "a life" or not. With artificial technology able to create a full compliment of DNA in a cell, the definition of inception becomes problematic.

The religious view of the beginning of "a life" is often at the point of conception, though there are issues in some religions connected with earlier stages and the religious implications of artificially preventing conception, i.e. Birth Control.

An alternative starting point can be that life does not begin until later stages of the human life cycle. Medically, the point of implantation is the point it is termed a pregnancy. This distinction recognizes that fertilization regularly occurs without implantation and for an entirely natural reproductive process, successful implantation must occur to be successful.

A later stage of development that, for some people, finds alignment with the idea of "a life" is the earliest point that a heartbeat can be detected.

Another stage of development that has been discussed is the point at which a fetus is sufficiently advanced that it is capable of surviving outside of the womb. This discussion does not address issues related to the quality of life and the possibility of compromised mental and physical development due to premature separation of fetus and mother.

The legal definition of the beginning of human life is primarily raised in connection with the legality of abortion or the termination of a human pregnancy.
A few decades ago, the legal system in some States in the US chose 25 weeks the point that "life begins.". However that is constantly changing.
Some countries have laws which make abortion illegal at any time and some countries permit abortion without regulation.

Answer 2

When life first originated is still a debated topic among scientists. Originally life was thought to have begun around 3.5 billion years ago, based on ancient microfossils that were thought to be early examples of life. As it turned out, these microfossils may actually have been of non-living structures, so the time when true life first arose will have to shift somehow.

We may never know exactly when life began because Precambrian fossils are rare and microscopic life rarely leave behind fossils.

Answer 3

It seems that life on planet Earth began some billions of years ago; fairly soon after the formation of the Solar System.

This question may be about human Biology, etc.

For humans, life begins at the moment of conception, when pregnancy begins.

That is, when the egg is fertilized.

There is the related question about when an embryo is "really" human.

That's connected with debates about abortion, of course, and is still controversial.