If humans did not know how babies were made, it would certainly have a significant impact on our ability to reproduce, but it wouldn't necessarily mean that humans would cease to exist on Earth.
Before the development of scientific knowledge about reproduction, humans, like other animals, would still engage in sexual activity and conceive children, even if they did not fully understand the biological mechanisms behind it. Throughout history, various cultures and societies have had different beliefs and myths about the origins of life, often attributing it to divine or mystical forces.
Without the knowledge of how reproduction works, there might be challenges in understanding fertility, controlling family size, or addressing certain medical issues related to pregnancy and childbirth. There could be higher rates of maternal and infant mortality due to a lack of proper medical care and understanding of prenatal and postnatal care.
However, humans are intelligent beings, and our survival instincts would likely drive us to observe and adapt to natural patterns in procreation, leading to the continued propagation of our species. Over time, trial and error, observations of animals, and other factors could lead to the discovery of methods that support reproduction, even if the actual biological processes were not well understood.
It's important to note that throughout history, knowledge has been accumulated, shared, and passed down through generations, enabling us to better understand our biology, improve healthcare, and control reproduction. So, in the absence of this knowledge, our progress as a species might have been slower, and the path to modern human existence could have been quite different, but it is likely that we would still find ways to survive and continue our lineage on Earth.