From “Armed sibling rivalry among suckling piglets” by David Fraser and B. K. Thompson (from Agriculture Canada)
A piglet’s most precious possession
Is the teat that he fattens his flesh on.
He fights for his teat with tenacity
Against any sibling’s audacity.
The piglet, to arm for this mission,
Is born with a warlike dentition
Of eight tiny tusks, sharp as sabres,
Which help in impressing the neighbors;
But to render these weapons less harrowing,
Most farmers remove them at farrowing.
We studied pig sisters and brothers
When some had their teeth, but not others.
We found that when siblings aren’t many,
The weapons help little if any,
But when there are many per litter,
The teeth help their owners grow fitter.
But how did selection begin
To make weapons to use against kin?