I'm sure Mendellian genetics apply. It becomes easier when a friendly one from a line of 20 friendly ones is bred to the same. I have birds that will walk away from food to come see me.
Most friendly chicken breeds - Page 9
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The PBRs are by far the most friendly in general. One Buff Orp was also a lover.
I had several very aggressive English Blue Orps. Got rid of all of them.
The current EBO and Australorp are very friendly but don't want to be touched.
I have the same experience with my Speckled Sussex. She came from a home not well handled, and has been the friendliest hen of the bunch beside my Delaware.
I've had very social friendly Speckled Sussex hens, and roosters of the same genetics either naughty or nice. Half bad boys, half respectful; a very individual story. Breeds and families do differ, and then training will develop behaviors that you want, again depending on what the individual bird can do. Bantam Brahmas and bantam Cochins have been nice too. Mary
And this goes for any breed of chickens-
The more time you spend with them when they're chicks, the friendlier they'll be grown up.