Concerning appearances, color, form, and function . . .
Obviously, color has no positive bearing on performance. There is no negative correlation either. There is neither a positive or negative effect. Color is never a factor. Breeding choices can be, so if color is prioritized to the exclusion of productivity, then selection is the concern. It is an elementary view that associates color with production traits. They are unrelated and there is no positive or negative effect on production itself.
Concerning form. Form is a necessary consideration. Pluck all of the commercial layers you can get your hands on and you will find a very uniform type. Pluck a selection of commercial Leghorns and you will find a similar type that is uniform in conformation. This is not coincidence. Commercial geneticists have narrowed down the most productive and efficient type. Enough of everything, and not too much of anything. Longevity with these birds is a separate and related consideration.
It is no coincidence that these have the type, though smaller, of the Standard Leghorn. The Leghorn breeders got it right. It is also not a coincidence that production bred Reds etc. evolve towards a more Leghorn type.
Conformation of form is not unique to laying fowl. It has always been a primary driver behind table fowl. Uniformity of quality is always a concern. Commercial meat strains have their unique and uniform type. Their type has become the standard of modern table fowl.
In the past, breeds bred and raised for the table had their own unique type. A good example was the English Sussex. The English was ahead of much of the poultry breeding world with this excellent (for their time) table bird. If anyone was to review the Standard, or knew the breed, they know that they have a cinderblock shape. These proportions allowed a meaty bird to sit flat on a plate. They did not want a bird that would role around on a plate. They wanted a particular type, for a particular reason, on a particular bird. They were after all, dual purpose table birds.
Pure function is often driven by unseen characteristics. Rate of growth, rate of sexual maturity, lay rate (or cycle), length of molt, etc. etc. etc. are considerations of their own. They can be had (in a limited way) in addition to, or excluded from the points above. All of these have to be evaluated on their own. They come together to make a productive bird. Coupled with an appropriate type, their potential is maximized. A actively productive birds is the sum of it' parts. There are many necessary selection points individually evaluated.
Each on its own is unrealized potential.
Selecting for uniform conformation is selecting for uniform quality and purpose. It is when it is done to the exclusion of their active characteristics that a less productive bird is bred.
So form and function is two truths in parallel. The best birds are a marriage of the two. Form is not contradictory to function, and function is not contradictory to form. Form is the potential function, and function is the form in action.
