The argument from selfishness for secular morality (or A.F.S.F.S.M.) goes as follows.
IF you are alive and IF you care to continue doing so THEN you ought to engage in self care.
IF self care is worthwhile and IF some other organism contributes to caring for you THEN you ought to care for them right back as part of that self care in as much as no man (ant/zebra/wild dog/bee) is an island.
IF whether or not some person(s) contribute to your care is an unknown quantity (such as all humans who engage in a modern global economy) THEN all things being equal you should care for and about them to insure that care in every possible case.