An alternative view is that, if you make good handaxes, you'll have more money (or patronage), meaning your children have more resources and advantages. You may

An alternative view is that, if you make good handaxes, you'll have more money (or patronage), meaning your children have more resources and advantages. You may increase your attractiveness to mates (who value their children's welfare). Beauty may be to do with simplicity. Simpler ways of seeing things (while retaining accuracy) are more likely to also be correct for situations not yet encountered - have better predictive powe, are better theories. Valuing those has a survival advantage. Simpler theories are also easier to learn, to use, to remember etc. It's very fundamental: our eyes, when confused by a scene at first, will resolve it to the simplest interpretation. I think this covers many instances of beauty (e.g. symmetry, neatness, non-arbitrariness, and even the simpler lines that emerge from averages), but it doesn't cover all. For example, the sworling of ocean waves, the complexity of clouds, of a forest. It is possible that these are in fact "simple", to the theories we have in our minds; just not simple for an intellectual understanding. And of course, fractal patterns are indeed simple, in the sense that they are generated by a very simple process. So, perhaps we somehow intuitively grasp the simplicity of clouds, waves, trees. (Or maybe we just like nature.)