In a 2007 paper, Charles Lineweaver develops Rare Head Theory:
We can use Fig. 4 to identify trends in the evolution of life, or convergences on some specific feature, whether it be E.Q., N.Q., olfactory lobe size or eyeballs. First we randomly select a few of the ~60 branches shown. Then we determine if two or more of them have independently evolved the feature of interest. For example, human-like intelligence probably depends on the existence of heads. Thus, we want to know if the tree of life shows any convergence towards heads. If heads were a convergent feature of evolution one would expect independent lineages to evolve heads. Our short twig on the lower left labeled “Homo” has heads, but heads are found in no other branch. Our two closest relatives, plants and fungi, do not seem to have any tendency toward evolving heads. The evolution of heads (encephalization) is therefore not a convergent feature of evolution. Heads are monophyletic and were once the possessions of only one quirky unique species that lived about six or seven hundred million years ago. Its ancestors, no doubt possessed some kind of proto-head related to neural crests and placodes (Wada 2001, Manzanares and Nieto 2003).
Drake (2006) stated that “[intelligence] is not a fluke that has occurred in some small sub-set of animal life.” However, Fig. 4 shows that intelligence, heads, even all animal life or multicellular life, may well be a fluke that is a small sub-set of terrestrial life. One potential problem with this conclusion: It is possible that existing heads could have suppressed the emergence of subsequent heads. Such suppression would be difficult to establish.
As they say, “as they say, read the whole thing”. I’m adding “The Subsequent Heads” to my list of potential transhumanist band names.