Chapter 9 Family Matters

For humans the pinnacle of unconditional love may be that between a mother and her child. Still, even the most devoted nurturers among us must be impressed by the Australian social spider. Soon after giving birth to about a hundred hungry spiderlings, Mom’s body literally liquefies into a pile of mushy flesh. The babies then munch on the flesh so they can start their lives with full bellies.

All things being equal, the genes living in the mom would prefer to live for another day. All things are not equal, however. The death of the mom, although costly, is more than compensated for by the head start it gives the many babies, each carrying copies of Mom’s genes.

Genes have built parents that "selflessly" give everything for their offspring, but this isn’t the only way to show family devotion. Organisms share genes with cousins, aunts, siblings, uncles, and more, too. We ought to see animals that also make sacrifices for these relatives, and we do–all the time.

Among turkey-like Tasmanian hens, many females live with just one male, but there is also a large number of polygamous females that keep a pair of males on hand instead. This female literally rules the roost: she allows both males to mate with her and requires both to provide food for her babies. This is a pretty sweet arrangement for the females. One study found that hens with two males had an average of 9.6 babies, while those with just one guy managed only 6.6 babies.

Do the males protest? To the contrary. Beyond merely tolerating it, they seem completely unruffled by their Three’s Company arrangement. Even some of the biggest males welcome small competitors into their nest with little objection. Why? ...

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