Chemical prokaryotes tend to be bigger. They have a larger plasmid (circular chromosome) to carry all the genes they need to express several different chemical pathways. This is actually becoming a bit of a problem, as groups of genes which work well together are getting longer and longer as well as more numerous. You need some way to pack them in better. Genes are often thousands of times longer than they are wide, resembling massive threads, and one well known way to tidy away threads is to wind them on a spool. There are several different chemicals which can act as a spool, but two in particular stand out with the lower cost for a given functionality. One costs more, but allows more efficient packing, and is called histone. The other is called HU.
Evolution starts with the Last Universal Ancestor.
You can find out what happened before evolution here.
You can also short-cut to Land plants, or Animals
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