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Both events need a settlement, so the question is which one a settlement produces first. A dog on Mars needs spare mass on a crewed ship, a dog-sized pressure suit that does not exist, and a reason; a baby needs a pregnancy carried to term in 0.38 g under a radiation load nobody has tested in any mammal, a decision no agency has signed off on, and nine months inside a base that already works. History leans one way: dogs went to orbit before people (Laika 1957; Belka and Strelka 1960, the first recovered alive) and were dropped from spaceflight the moment people could fly, and no animal has walked on the Moon in the 58 years since Zond 5's tortoises circled it. A dog arrives on Mars as company rather than science, which means a long-stay base, and the first baby needs the same base plus a medical decision that comes years after it. 63% for the dog first is reasonable; what would flip it is a settlement that bans pets before it bans pregnancies, a rule nobody has written. Dogs are also the first species in lifespan trials of anti-aging drugs, for the same reason: we test on them before we test on ourselves (mine): https://w0lph.github.io/k9/trials/