Now you’re peering down the rabbit hole. Indeed, eukaryotes do exhibit a remarkable tendency to evolve multicellularity. And this insight leads to possible areas of inquiry (“maybe the first lifeforms included eukaryotes”) if you’re willing to question established views (“but of course that didn’t happen”).
More on this in future threads.
[Edited to add:]
Looks like I reached my posting limit for today. One last reply for @Ashwin_s, then I’ll take a break:
Thank you for the welcome.
I suppose I’m something of a “methodological designist”. Just like the shell model of the atom doesn’t have to be “true” to generate insights, I’m less interested in the ontological nature of the designer (“Is it a god? Aliens? Just a useful heuristic?”) than in exploring the theoretical space opened by considering the possibility of design.
I wouldn’t say that. It’s only happened 5 times out of all the many lineages of eukaryotes, and the vast majority have remained unicellular. It’s just more than any prokaryotes have ever done.
You mean if you’re willing to completely ignore all the data and free yourself from any rational hypotheses? As James Oberg said, “Keep an open mind, but no so open that your brains fall out.”
I must ask you to stop speaking in riddles. What hypothesis are you arguing for? What are you trying to say here? Oh, and which “once” was your job? Was the world intended as a playground for red algae?
The common genetic code. The large numbers of proteins and RNAs in common. And of course the mitochondrion, if you want to count its ancestry as being part of eukaryote ancestry. Why? Is there any doubt?
Why, yes I have. A very interesting critter, this sometimes-multicellular slime mold. Had its genome sequenced in 2005 (Nature 435, 43-57). What I found interesting was the presence of three G-protein-coupled surface receptor families that was thought to be specific to animals, and which seems to have been secondarily lost in fungi.
The hypothesis which I am ready to adopt as a tentative working hypothesis is that the first life on Earth was designed with multicellularity in mind. I would love to be able to extend this hypothesis to specific types of multicellular organisms, but I’m on shake ground enough as it is. So for now, I’m perfectly willing to accept that the designers had an inordinate fondness for red algae.
Doubt? No, not among mainstream evolutionary biologists.
PS. I think the evidence for the bacterial origin of the mitochondrion is pretty darn solid.
As I mentioned before, the problem with this hypothesis is that it would be difficult to design (or evolve) first life so as to forbid multicellularity. Multicellularity has two main components: intercellular communication and cell adhesion. Both of these are found in prokaryotes, as are simple forms of multicellularity. How would you prevent either from evolving?
“These numbers illustrate that conserved ribosomal proteins have highly diversified structures and carry many appended segments in the three domains of life. Even relatively simple bacterial species carry nearly as many residues within unique structural protein features as they carry in the conserved core, suggesting high degree of functional specialization of ribosomal proteins in each domain of life (fig. 1). These unique structural elements represent protein segments, whose lengths vary from a few to a few dozens of residues and which are typically exposed on a protein’s surface. These segments are so abundant that nearly every of the 33 conserved proteins carries at least one variable segment in each domain of life.”
The authors worry that standard alignment programs fail to capture these differences. I’ll send you the paper.
Note that these are differences in homologous proteins, each of which has a largely invariant core sequence. That paper doesn’t talk about the non-homologous proteins at all except for a brief mention in the intro.