Most of the great and significant philosophers since Descartes were childless - if not genetically, then practically, they played no role in raising their children. Descartes himself had an illegitimate daughter - besides that, the list of childless encompasses almost all of the modern philosophical greats. Spinoza, Leibniz, Locke, Hume, Kant, Schopenhauer, Nietzsche, Wittgenstein. Against that you can balance Hegel, Marx, Russell and Heidegger, and there are probably more arguments over whether to include any of the second list (excepting maybe Hegel) in “philosophical greats” than the first list.
I’m not arguing for any causal link besides the pressure of time (kids take a lot of it, as does being a leading figure in almost anything) and the sort of personality that gets a long way in philosophy perhaps not being amenable to standard family life. While Hume would by all accounts have probably made a good husband, Nietzsche would almost certainly have been insufferable, and Wittgenstein, ah, wasn’t the marrying kind.
Speaking from my exerience, having children affected my outlook on life, convictions and expectations of how humans think and feel about other beings, of the hardness of the boundary between Self and Other. A seemingly facile statement about self-interest being paramount in all living beings takes on a different aspect, and it’s only by contortions of genetic reductionism that people can explain why it is hardwired to be in one’s self-interest to promote one’s children - but that isn’t what is meant by the atomism of many philosophers on the subject. There is an aspect of interpretation that is fundamentally different; maybe veering dangerously close to phenomenology, there is an experiential change. At least, many people I’ve spoken to and read have described how having children forced them to pull their head out of their arse and get on with real life.
I’m not arguing that everyone should breed, or that it’s a definitive act or in some way imparts additional value to ones thoughts and desires. But given that it’s such a large part of human experience, a necessary one for its continued existence, is it not strange that so much of what we think and so many of the terms in which we define and conduct our discussions were created and formulated by people who never experienced it? Is it maybe a variable that should be considered in the study of a body of philosophical work - just as we often consider the age, social background and historical/philosophical milieu of a thinker to place his ideas in context*?
[size=66]* I left out “sex”, and used “his” consciously, in acknowledgement of another underrepresented majority… [/size]