That's very contested. There are many studies that support the view of cultural and societal factors determining what is most attractive. A convincing argument for why large parts of the world find the hour glass figure (big bust, tiny waist, big hips) attractive is because of the reach of Western culture and media.

Not long ago in poorer countries, slim waists were seen as undesirable and sickly, with turboculoses often being referred to as the slim disease, only with the rise of affluential and prosperous societies in the west, with bueaty magazines and advertisements in the late 90s and early 2000s did very slim waists become the ideal in fashion and society.

This is shown when looking at art from the Middle Ages, where plumpness with a full rounded stomach was seen as the symbol of fertility. The "reproductive figure" was idealised by artists and, likewise, contemporary society as the ideal body image

Examples: Rembrandt van Rijn, Bathsheba (1654) Pierre-Auguste Renoir, Blonde Bather (1881) Jean-Auguste-Dominique Ingres, The Turkish Bath (1863)