Are there any other "agnostic" types here who look at evolution as an extremely dubious theory?

Sad that an entire book was written based upon that. Cairn's phenomenon has been studied and is extremely well understood. You can read a paper about it here open access. A short version: the lactase gene was mutated in this bacteria to inactivate it, but it still had some tiny trace of activity. This trace activity provided a benefit to the bacteria when chance duplications of regions of the genome produced in some bacteria multiple copies of the broken lactase gene (not as good as a fully-functioning gene, but enough copies of the mutated protein would allow bacterial growth). The presence of multiple copies allowed chance mutation to hit upon the reverse mutation more rapidly than expected, like buying multiple lottery tickets. Voila, apparent "directed" evolution. There is a concrete record for every step of the process, with the intermediate genotypes studied and the steps of the transition reported in this paper.

Why should I believe this world is 50 million years old?

Psst--4.5 billion years old. You have to go back further than 50 million years just to find the dinosaurs.

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