Beauty is not an easy concept to well define and it may be so relative and personal a universal objective definition is impossible. Many confuse it with sexual attractiveness, but before you can be making statements like that you need to formulate a well thought out canon of beauty. Statements like male and female forms are equally beautiful might be correct according to such a canon, but without the canon such statements are merely PC feel good equality of the sexes opinions.
Why not take a shot at stating your canons of beauty first, and then make the applications? In the end I agree it will all be relative to the individual observer, but nevertheless there should well be some objective standards that apply across most of the subset of humans concerned with aesthetics.
Personally I do agree that the ideal male and female figures are both beautiful as exemplified in Greek sculpture and a very few photographic examples of exceptional humans. Aesthetics is a very tricky concept difficult to divorce from the implied dynamic function and evolution of the forms involved. I'm not even sure it can be.
There are two different meanings of the word 'average'. In the sense of most ordinary it is not normally thought of as beautiful, but in the sense of an actual morphed average of say faces one quickly sees an amazing emergence of the beautiful archetype underlying the human form. A big big difference.
I've always said that when it comes to feminine beauty God came up with an absolutely exquisite blueprint. It's just the quality control that is abysmal!
The exquisite blueprint of ideal perfect beauty tends to very quickly emerge from morphed averages as can be seen at this fascinating site:
http://www.faceresearch.org/demos/average. In contrast the most ordinary is just the most frequent mistake in executing the blueprint!
Some would argue that human females are no more beautiful than any other primate female since beauty is in the eye of the beholder. Well, I had assumed I was speaking to humans, but perhaps I was mistaken? :-)
That being said this statement assumes that other animals have equivalent concepts of 'beauty' as humans do. There is a big difference between sexual attraction and an abstract concept of beauty, which is what I was referring to. My suspicion is that humans have that much more than other species due to their greater abilities to consider forms abstracted from real world shapes in isolation from the objects which embody those forms.
I personally agree that horses are among the most beautiful of animals. But why is that, that's the question. is it the efficient manifestation of function, or only the integrity of the form?
In my experience almost everyone who has expressed an opinion, both men and women alike, view pro bodybuilders as ugly freaks, the very antithesis of male beauty. I'll go with the Greek statuary ideal any day which always portrays the ideal man with a good set of muscles covered with a natural and healthy layer of body fat - not to mention nobility of visage.
There very big difference between physical existence and a quality of perception that depends on the perceptions of some observer. Three boulders might be there but they would be neither soft nor hard because that describes not the boulders but how they are sensed by some observer. Same with beauty. It does not exist unless it is perceived by some mind attuned to that perception in a particular manner we or it calls 'beauty'.
Any theory of beauty must not just encompass female human beauty but mathematical beauty and the beauty of ideas and natural forms as well. Ultimately it is dependent on human cognition which perceives it but it has generally been argued that there must be some hidden universal characteristics that make some particular things of all types beautiful.
Elegant simplicity of form that best encapsulates and clearly reveals some type or category of form in its essential nature is my first cut at a definition of beauty.
What's your definition of beauty?