Recent research concerning tyrosine kinases continues to strengthen the case for front-loading evolution:

When it comes to cellular communication networks, a primitive single-celled microbe that answers to the name of Monosiga brevicollis has a leg up on animals composed of billions of cells. It commands a signaling network more elaborate and diverse than found in any multicellular organism higher up on the evolutionary tree, researchers at the Salk Institute for Biological Studies have discovered.
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This treasure trove of diverse and novel tyrosine kinases took the study’s lead author Gerard Manning, who heads the Razavi-Newman Center for Bioinformatics, by surprise since it was long thought that tyrosine kinases are restricted to multicellular animals where they handle communication between cells.
“We were absolutely stunned,” says Manning. “Based on past work, we had expected maybe a handful of these kinases but instead discovered that this primitive organism has a record number of them. Two other essential parts of the tyrosine kinase network - PTP and SH2 genes - are also more numerous than in any other genome, showing that it is the whole network that is elaborated here.”
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The Monosiga kinases are more divergent than anything previously seen in animals, which may help scientists understand the fundamentals of how all tyrosine kinase signaling works. Despite their extreme diversity, Monosiga kinases time and again arrive at the same solution to a problem, as do animal kinases, but using a distinct method for instance to create a sensor structure that emerges from the cell, or to target a kinase to a specific part of the cell. “This convergent evolution suggests that there are only a limited number of ways build a functional network from these components,” says Manning.

With all this new information, one obvious question remains unanswered: what is a single-celled organism doing with all this communications gear? “We don’t have a clue!” says Manning, “but this discovery is the first step in finding out.”

That a single-celled organism contains a signaling network more elaborate and diverse than found in any multicellular organism clearly indicates the plausibility of such an ancestral, front-loaded state. What’s more, note that the system has been set up such that similar outputs are reached through convergent evolution. I’ll be commenting on this in more detail a little later.