Any breed can become flighty or person aggressive through not taking inherited genetics into account. I wanted to know why people were having problems with their roosters so I started lurking on other forums that have lots of roosters, that is when I learned just how amazing chicken behaviors are... so many are genetically linked. I also suspected we create issues not understanding bird body language, bird thinking versus human thinking, and how we can create and reinforce bad behaviors... this was also confirmed hanging out in other places.
Things I have learned:
Breed for what you want applies to behavior... never use a hen or rooster no matter how perfect in other respects that attacks people unless you have reason to believe this behavior was learned (animal mistreated) or no choice. You are going to have what is called "man eaters" birds in a higher percentage.
Birds that are gentle but whose offspring seem to produce hostile (towards human) offspring should probably be dropped from breeding program.
Most folks do not breed egg eater hens as they have seen that trait passed down. If you do want to you need to build a roll away nest box so you get the eggs and try and break the cycle by hand raising and keeping the offspring of egg eaters away from hens that might teach that bad habit. But many swear the problem is genetic others swear it is learned, nutrition based, and people not collecting eggs regularly.
Observe your birds, what behaviors are healthy, normal, what ones exhibit unhealthy behaviors... example birds that do not preen should not be bred. Birds that preen normally are usually healthy animals. The behavior is apparently genetic.
If using birds with behaviors you don't want but crossed with ones you do, cull heavily the offspring based on the behaviors you don't want and if possible back breed the keepers to parent with behavior you like.
I just find it amazing what can be bred for... broody versuses not broody, how they react to stress (do they run, fly, turn and face it, play dead?), flighty versus not flighty, human aggressive versus human gentle, bird gentle versus bird aggressive, and more.
I am also convinced though from roaming around in general on bird behaviors in captive pet breeds or domestic breeds like chickens we may create problems by not understanding bird thinking or bird body language. Chickens do do things other species of birds do concerning general body language, plus they have some unique moves, calls too... I found a video were the keeper showed the difference in body language between two roosters one a "man eater" and one not, he showed how to tell you are about to be attacked even.
I think we may accidentally stress birds out into being less friendly sometimes too. I know parrots are not Chickens but I started watching body language and training videos aimed at not stressing parrots out in the bonding traing process and realized some of the no nos probably apply to chickens, also big bird body language things they both do. I have adjusted my interactions with my hens and the result has been friendlier hens. A lot of training practices are based on making an animal do what you want by what the animal might understand as aggression from it's perspective so you don't get the results you want... to train gently you got to understand the critter, humans try to take short cuts, if I have learned anything over the years patience and understanding the animal on it's terms are the two keys to animals responding correctly. We boast how darn smart we are but never ever bother to learn our pet's language and then wonder why it all goes pear shaped... just saying the more you observe, the more you try and understand the behaviors they do the better you can train any animal becuase you begin to think more like it does, see the world a bit different.
So when I want my hens to come check out a treat or food I put down I bend over peck the ground with my hand and make a call mother hens use for chicks to come and get it. I then step back, usually they run right over to see what treat I have just put down.
I have taught them "go home" means go into their coop with saying it every night while offering a treat reward. The up is it need not be chicken bed time for them to understand I want them to go into the coop early for some reason. They are not always happy about early bedtimes but they will go inside their coop.
Are my birds perfect, no, but in all cases where my birds have done things I don't want them doing behavior wise I am usually boneheading something, and once I figure out what has stressed my birds, or what my birds need that I am not supplying the problem goes away.
Just my rambling thoughts on the nature vs nurture battle, which need not ever be a battle.
