The Frailty of Adaptive Hypotheses

Earlier I noted that Michael Lynch has doubts about whether natural selection was responsible for the evolution of multicelluarity:

These results, along with our theoretical work on network evolution, challenge the popular idea that modularity arises as a direct consequence of selection for morphological complexity, and by extension raise questions about the common assumption that natural selection was responsible for the emergence of multicellularity.

A couple of years ago, Lynch published a very interesting article entitled, “The frailty of adaptive hypotheses for the origins of organismal complexity” in PNAS (2007) vol. 104, pp. 8597–8604.  You can read the article here.

A couple of excerpts relevant to the evolution of multicellularity are below the fold.

Connecting the Pieces

I really wish I had the time to write more detailed postings for y’all.  For example, last night I drew attention to some recent findings that further support the plausibility of front-loading and seamlessly connect with other proposals on this blog.  But I didn’t get a chance to flesh it out.  So let me add a little more flesh to those front-loaded bones and show specific points where this ties in to my views.

More ‘Evidence’ of Front-loading Mitochondria

I have previously shared some evidence for the front-loading of mitochondria, along with an emerging picture where symbiogenesis is merged with front-loading. Now there is yet some more evidence in support of the plausibility of front-loading mitochondria.  Those who follow this blog, or have read The Design Matrix, will note how seamlessly this all fits in with my hypothesis of life’s design:

Yet Another Prediction

SYMBIOGENESIS

Symbiogenesis is a theory of evolution. It argues that symbiosis is a primary force of evolution, because acquisition and accumulation of random mutations or genetic drift are not sufficient to explain how new inherited variations occur. According to this theory, new cell organelles, new bodies, new organs and new species arise from symbiosis, in which independent organisms merge to form composites. This challenges some standard textbook ideas of how evolutionary change occurs. To some degree, Darwin emphasized competition as the primary driving process of evolution, symbiogenesis emphasizes that co-operation can also be important to the process of evolution.

It is now very reasonable to propose four major events of symbiogenesis:

1. The origin of double-membrane (gm neg) bacteria.

2. The origin of the eukaryotic cell.

3. The origin of mitochondria.

4. The origin of chloroplasts.

A Key Hypothesis

James Lake was recently proposed and supported a fascinating new hypothesis:

Lake has discovered the first exclusively prokaryote endosymbiosis. All other known endosymbioses have involved a eukaryote — a cell that contains a nucleus. Eukaryotes are found in all multicellular forms of life, including humans, animals and plants.

[…..]

In the Nature paper, Lake reports that two groups of prokaryotes — actinobacteria and clostridia — came together and produced “double-membrane” prokaryotes.

“Higher life would not have happened without this event,” Lake said. “These are very important organisms. At the time these two early prokaryotes were evolving, there was no oxygen in the Earth’s atmosphere. Humans could not live. No oxygen-breathing organisms could live.”

Here is the abstract for the paper:

Endosymbioses have dramatically altered eukaryotic life, but are thought to have negligibly affected prokaryotic evolution. Here, by analysing the flows of protein families, I present evidence that the double-membrane, Gram-negative prokaryotes were formed as the result of a symbiosis between an ancient actinobacterium and an ancient clostridium. The resulting taxon has been extraordinarily successful, and has profoundly altered the evolution of life by providing endosymbionts necessary for the emergence of eukaryotes and by generating Earth’s oxygen atmosphere. Their double-membrane architecture and the observed genome flows into them suggest a common evolutionary mechanism for their origin: an endosymbiosis between a clostridium and actinobacterium.

This hypothesis is fascinating whether we look backward or forward from the proposed event.

The Appendix – another example of convergent evolution

Using a modern approach to evolutionary biology called cladistics, which utilizes genetic information in combination with a variety of other data to evaluate biological relationships that emerge over the ages, Parker and colleagues found that the appendix has evolved at least twice, once among Australian marsupials and another time among rats, lemmings and other rodents, selected primates and humans. “We also figure that the appendix has been around for at least 80 million years, much longer than we would estimate if Darwin’s ideas about the appendix were correct.”

- Here

The Logic of Evolution

A few months back, Simon Conway Morris wrote:

Indeed it is now legitimate to talk of a logic to biology, not a term you will hear on the lips of many neo-Darwinians. Nevertheless, evolution is evidently following more fundamental rules. Scientific certainly, but ones that transcend Darwinism. What! Darwinism not a total explanation? Why should it be? It is after all only a mechanism, but if evolution is predictive, indeed possesses a logic, then evidently it is being governed by deeper principles. Come to think about it so are all sciences; why should Darwinism be any exception?

Front-loading Hedgehog

The hypothesis of front-loading continues to gather traction.  Consider this description of the Hedgehog signaling pathway:

In a growing embryo, cells develop differently in the head or tail end of the embryo, the left or right, and other positions. They also form segments which develop into different body parts. The hedgehog signaling pathway gives cells this information that they need to make the embryo develop properly. Different parts of the embryo have different concentrations of hedgehog signaling proteins. The pathway also has roles in the adult. When the pathway malfunctions, it can result in diseases like basal cell carcinoma. [1]

The hedgehog signaling pathway is one of the key regulators of animal development conserved from flies to humans. The pathway takes its name from its polypeptide ligand, an intercellular signaling molecule called Hedgehog (Hh) found in fruit flies of the genus Drosophila. Hh is one of Drosophila’s segment polarity gene products, involved in establishing the basis of the fly body plan. The molecule remains important during later stages of embryogenesis and metamorphosis.

So here we have a circuit that is essential to the development of metazoan body plans.  How in the world could we front-load this information into a single-celled organism?

Black Hole

Defining Intelligence

This is not it: