I don’t think “it can’t continue living on its own” is a good measure of whether or not something is alive or a separate organism. Even after birth a baby human can’t “continue living on its own” without being provided for. A parasitic creature can’t “continue living on its own” without a host. A severely injured person can’t “continue living on its own” without life support. Pretty easy argument for even a stupid forced-birther to deconstruct.