Knowing the conditions of the early Earth, I could say that the least evolved are the chemoautotrophs. But which of the three is most evolved or most recent? Please correct me if I am wrong.
Thank you.
Since we can only guess at what early microbes existed based on those whose descendants are still with us, the conventional wisdom is that the early microbes were thermophilic chemoautotrophs. These organisms seem to dominate the lower phylogenetic branches of both the Bacteria and Archaea.
As for most evolved, that is a bit of a trick question. One could answer that since evolution is an ongoing process, the descendants of the earliest microbes are by definition also the most evolved. If I had to wager, I would guess that the last physiological type to first arise would be the photoautotrophs. It would seem to me that it would be a relatively easy path to chemoheterotrophy from chemoautotrophy.
I get your question, and I agree with you and John Wertz above that chemoautotrophs likely came first.. and perhaps photoauototrophs were the last of those types to show up. But if two separate lineages changed from chemoautotrophy to one of the others, which one would you say is more derived? Sort of a tough call...
Be careful when using language like that about evolution. If one accepts that all life has a single origin, then this means that all life has been evolving for the same amount of time. The lineage leading to the bacteria in your gut has been evolving for just as long as your lineage. If derived states are what you're after, then make that your ambition.
edit: typos
As other's have said, I'd be careful about using words like 'most' or 'least' evolved. I am not more evolved than an earthworm when it comes to living in the soil, as it is very well adapted to that environment. I think you mean the one with the most derived characters relative to some putative ancestor.
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