I like puzzles. One thing that drew me to the study of evolution was that it is effectively an intricate mesh of puzzles, with some less-than-obvious yet neat solutions.
But I think what keeps me coming back to it is the raft of conceptual challenges, coupled with the desire to place it all in a coherent framework. The logic behind mathematics and physics, for example, is largely straightforward - except at the outer limits (such as relativity, cosmology, quantum physics).
By comparison, evolution is a constant challenge, in a number of ways.
First, deanthropocentrism. To attempt to make sense of the narrative that is evolution, it is necessary to mentally free ourselves from our human frame of reference. Many accept creationism simply because it's hard to conceptualise mutative changes that happen on the scale of millions and billions of years. After all, human history only extends a few thousand years, and modern humans have only existed for a scant hundred thousand years - yet we are the product of those billions of years that came before.
It's not just time that we need to reconceptualise. There's also the other scales at which evolution is working: DNA, and the chemical factories that it sets up in each living cell. Viruses and bacteria, and the contribution their rapid mutations make to other species, and to the overall environment. And the part played by the complex interactions of species at all levels that are competing for living space.
Evolution also holds a number of unexpected surprises: a seemingly unconnected set of principles that come to play in building up the narrative. Convergent evolution. Viral insertions into germlines. Dual functionality for organs. Terraforming bacteria. The relationship between the rate of evolution and solar radiation. The difference between, say, the human eye and the octopus eye.*
Understanding a number of disparate strands in the evolutionary narrative requires a lot of reading. You will find that the same stories come up time after time in explaining principle, yet there are always new stories and new explanations. But not only is it useful to read widely on evolution: it also helps to draw in parallels from other disciplines and experiences, to make sense of new concepts through associativity, drawing similarity with other strands of knowledge.
Readings of Gould, Dawkins et al only hinted to me at the nature of the challenges that awaited. Gould certainly does discuss the need to reconceptualise. But to come from a different discipline that may be steeped in fairly direct logic, to one such as this where the logic is there, but works in often tangential ways, is something that a life-long biologist often does not appreciate enough in communicating to a non-biologist.
Logic is the fundamental basis of evolution, of course. But understanding calls for more: experience, metaphor, imagination. It's easy to grasp the headline explanation of evolution, but the headline alone doesn't draw all the requisite strands together: there is so much that can make a lot more sense if one drills down.
And it is ultimately immensely rewarding to find that the more conceptual barriers are crossed, the simpler and neater the narrative turns out to be.
*If I mention anything here for which you haven't seen adequate explanation yet, let me know: I'm happy to dwell on it :)