theory-2
Explanation
This comic parodies cosmological debates — specifically the Steady State theory versus the Big Bang theory — by mapping them onto a child's question about where babies come from.
In the panel, a child proposes what sounds like a reasonable idea (presumably that parents were once children themselves), but another child objects: "The problem with your idea is it puts us in a privileged position with respect to time. Why should we assume parents were kids in the past, rather than eternal and unchanging?"
This is a direct parody of the Steady State model of the universe, which was championed by Fred Hoyle and others in the mid-20th century as an alternative to the Big Bang. The Steady State model held that the universe has no beginning or end — it has always existed in roughly the same form, with new matter continuously created to maintain a constant density as the universe expands. One of its philosophical motivations was to avoid placing any particular moment in time (like a "beginning") in a special or "privileged" position.
The caption drives the joke home: "Among researchers, this is known as the Steady State Model of Where Do Babies Come From." The humor lies in applying a sophisticated cosmological argument to an absurdly mundane question. The child's insistence that parents are "eternal and unchanging" rather than former children is logically structured the same way as arguing the universe had no beginning — and sounds equally silly when applied to something we can directly observe.