Tyrosine kinases and front-loading

Back in 2002, a scientist who was skeptical of my front-loading hypothesis, asked me:

So the question arises: how much of the control machinery governing development in (for instance) metazoans could plausibly serve a useful role, and thus be maintained by selection, in unicellular organisms?

Then in 2005, another scientist who was skeptical of my front-loading hypothesis, was even more specific:

It seems to me that front-loading of genetic information makes the very strong prediction that we should find in the genomes of simple species remnants of genes whose functions are specific to complex species. If all of the genetic information to make vertebrates (for example) was front-loaded into the earliest bacterial species, followed by functional loss of information from the genomes of species that did not need particular genes, we should see remnants of at least some of those lost genes. Are there, for example, remnants of metazoan-specific genes found in the genomes of protozoa or bacteria? As far as I am aware, there are not. For instance, a search of genomes for a large class of metazoan-specific genes that encode tyrosine kinase receptors, a distinctly metazoan innovation (from the evolutionary perspective), reveals nothing in the way of related pseudogenes or gene remnants in any bacterial or protozoan genome. This is the sort of evidence that one would have to produce for the idea of front-loading to be taken seriously.

These quotes should help you to see that conventional evolutionary theory led scientists to predict that that tyrosine kinase receptors would be “a distinctly metazoan innovation” that co-evolved into existence alongside metazoa as such “control machinery governing development” in metaozoans would not be maintained in unicellular organisms.

Well, as some readers probably know, it turns out that this metazoan control machinery, the tyrosine kinase receptors,  are not a “distinctly metazoan innovation.”  And in fact, better that any pseudogene or gene remnant (which are not predicted by front-loading) is the discovery that single-celled organisms possees a tyrosine kinase toolkit.

And in case anything still thinks conventional theory led scientists to expect single-celled organisms would contain this control machinery, please note the initial reaction of one of the lead scientists behind this discovery:

“It’s amazing.” King says. “We interpret that as evidence that some of the protein machinery for multicellularity actually evolved before the origin of animals, before multicellularity itself. The proteins predated their current function in animals.”


“I was surprised to learn that so much of animal biology was in place before the origin of animals,” King says. “And I think that’s what motivates most scientists–not learning that you were right, but learning that you were wrong.”

I was not surprised.  That protein machinery for multicellularity actually evolved before the origin of animals is something I predicted from the hypothesis front-loading.  It’s no more suprising for FLE than also finding that the protein machinery for synapses actually evolved before the origin of synapses. 🙂

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