An old joke says "when the kids go to college and the dog dies."
Historically, most societies did not consider very young children to be fully human.
Their deaths were not mourned in the same way as deaths of older people and they were given little if any funerary treatment.
When human life begins is a social, not a biological fact.
Strangely (for us) in the history of humanity until recently, young people died more frequently than old people.
Next: On to swidden gardening
The idea that death is more associated with the young than with the old seems very odd to us, but it was a common fact until relatively recently. In most if not all societies before the last third of the 19th century, the mortality rate for people under 20 was between 40 and 50 percent. That is, between 40 and 50 percent of all children born alive would die before their 20th birthday. On the other hand, if you made it to your 30s, the odds that you would live to be 60 or 70 were pretty good. The implication of this is that in these societies, the odds that a 50 year old would be alive in a year were much greater than the odds that a 10 year old would be.
One more comment on when life begins: Scientists don't really agree on exactly what life is let alone when it begins. We often (but not always) know when an individual organism is born or dies. But the quality " life" itself? That seems more like a continuous biochemical process that flows through the world.
Taking the question "When does Life Begin?" literally leads to a clear but challenging answer: Life begins more than 3.8 billion years ago. The "life" that is in you (and is in the tree outside your door, and is in your pets, and is in everything we think of as alive) has existed in an unbroken chain since that time. There has never been a point in the last 3.8 billion years when the life that is in you today was unambiguously not life. Consider egg and sperm for a second. Egg and sperm are, in and of themselves not an animal. They are not alive in the same way an animal is alive. However, they do clearly contain the quality of life, whatever that is. Consider a seed. A seed is obviously not a plant. However, it, somehow, contains the quality of life. A seed or egg and sperm are fundamentally different from things that are not alive, like a rock or a pencil. The quality of life in plants flows through the seed.* The quality of life in mammals flows through egg and sperm. To reiterate, the life of a human beings (or any other living thing) has no "life begins." Life is always present, though we're not entirely clear on what it is. Thus far, although we've come tatalizingly close, we've never been able to create life from not-life.
The thing is, that in political and moral debates, people ask when life begins when they need to be asking when life is human. And, of course the problem is that the question "when does life begins" sounds (falsely) like it could has a scientific answer other than about 3.8 billion years ago. The question "when is life human" is clearly NOT a scientific question, but rather a moral and philosophical one. Different societies and different historical eras have given different answers to the question ranging from sperm and egg are morally human to (as the slide says) human life begins when the kids go to college and the dog dies. Maybe more troubling, different philosophical approaches to ethics give can give different answers as well. Broadly speaking there are three competing ethical schools: deontology (rule based ethics), consequentialism (ethics driven by attempts the results of decisions, often linked to utilitarianism), and virtue ethics (what would the virtuous person do). Following these lines of thought people can come to diametrically opposed conclusions about when life is human and there is no (non political) was of deciding between them.
If you would like to read a fascinating scientific treatment of the question, read Carl Zimmer's 2021 book Life's Edge: The Search for What It means to Be Alive.
*Of course, we are aware that plants and many (perhaps most) living creatures reproduce in non-sexual ways as well but for our argument here, we are focusing on sexual reproduction.