Any study of evolution necessarily involves theories, but if we stopped short with known facts our phylogenetic trees would wither at the roots. Particularly when we attempt to reconstruct events that took place in remote Precambrian times we can have recourse only to our imagination. Where connecting links between modern animals cannot be known, we must invent them; at least, if evolution is true, we can feel sure that connecting links really did exist. Imagination, of course, must be controlled by reasoning from the known to the unknown, but unfortunately our brains do not all reason in the same way and often produce very different concepts from the same set of facts. Yet some ideas Should be more plausible than others.
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