Wednesday, July 22, 2009

What is Medean Life?

I am going to post the points testable points that Ward puts out there as what makes life, by definition, Medean instead of Gaian. I will quote what Ward says as the actual hypothesis and then summarize what follows in his explanation. First, however, let's examine what Ward is arguing against: Gaian life. According to Ward there are 4 main variants on the Gaia Hypothesis:

1. Optimizing Gaia: This is where life is constantly improving the conditions which it finds itself. "It implies that there is actual control of environmental conditions, such as temperature, oceanic pH, and even atmospheric gas composition...Another way of interpreting this hypothesis is that the biomass alters conditions on Earth to increase the 'hospitality' of the planet." Life is the optimizer in this variant.

2. Self-regulating Gaia: This where feedback loops in the environment that life is involved in are negative feedbacks, allowing life to not necessarily control conditions, but adjust them. Ward states that the self-regulating variant of the theory "supposes that the feedback systems allow the continuation of life on Earth by keeping life-constraining factors such as temperature, and even recently even atmospheric oxygen and carbon levels ... within ranges that allow life." Life is the stabilizer in this variant.

3. Coevolutionary Gaia: "[I]t simply advocates that the biota and environment have evolved in a coupled way." This is the 'weakest' Gaia hypothesis Ward states and that is essentially considered true at this point. Life effects the environment and the environment effects life.

4. Progressive, Deterministic Gaia: "Once life evolved, there came into existence a few possible pathways for how life and its systems would evolve further...simply a small number of nutrient and element cycles that affected later life." Pretty much self explanatory.

Now, in contrast what does Ward predict for his Medea Hypothesis. What makes life Medean?
  1. "All species increase in population not only to the carrying capacity as defined by some or a number of limiting factors, but to levels beyond that capacity, thus causing a death rate higher than would otherwise have been dictated by limiting resources."
  2. "Life is self-poisoning in closed systems."
  3. "In ecosystems with more than a single species there will be competition for resources, ultimately leading to extinction or emigration of some of the original species."
  4. "Life produces a variety of feedbacks in Earth systems. The majority are positive, however."
  5. "Diversity and biomass can be independent and decoupled."
  6. "The history of biomass (not diversity!) should show a series of steps - from the first formation of life harnessing ever more energy through better metabolisms. After some period of time, however, each group of organisms that utilizes the new kind of [metabolism] will show a slow decay, to biomass levels lower than those following the initial diversification of organisms."
  7. "In all but regions of low environmental disturbance, ecosystems will eventually move toward lower species diversity as the competitive forms drive others species in extinction and as some species move into dominance."
pgs 29-37. The Medea Hypothesis. Dr Peter Ward.

In a quick summary, Ward holds that "life as an aggregate is negative to itself:" in essence, life, as a whole is suicidal and will shorten its existence faster than if it was not. It will use all of its resources up before any other influence - barring a freak occurance like a near by supernova - can do so.

Here's the start point of discussing Ward's extrapolations. First comments? Shots?

[btw, Carlos, he references Diamond. A lot.]

The Medea Hypothesis Review TOC is here


Mr. Greenbaum said...

Ward did work on the end-Cretaceous and the end-Permian mass extinctions and I did not, meaning that what I might say would be much more poorly informed than what he has said. Also, I haven't read the book, so I am therefore even less qualified to pronounce on the plausibility of the so-called "Medea Hypothesis" as put forward by Dr. Ward.

But I don't generally feel that the hypothesis is problematic.

Ward puts forward several episodes of global catastrophe caused by metabolism: a mid-Archean methanogenesis; late Archean oxygenogenesis; iceball glaciations in the early and late Proterozoic due to exhaustion of greenhouse gases in the oceans and atmosphere; multiple Phanerozoic environment changes due to multicellular plant and metazoan species turnover (end-Cambrian, Ordovician, end-Devonian, Carboniferous, end-Permian, and Holocene, to name several.)

That these environmental changes and mass extinctions can be causatively linked to the prevalence of a particular form of metabolism, the ramifying environmental influences of the appropriate chemistries, or the more-meta interactions of evolving multicellular plants and animals is unproblematic for the adherent to a weak coevolutionary Gaia.

The problem comes in when the stronger Gaias are on offer. The stronger Gaias posit deterministic linkages in homeostatic feedback mechanisms - linkages that moderate environmental deviations and promote returns to life-friendly equilibria.

The history of Life has been a history marked by episodes of development, consolidation, catastrophe, and eventual recovery. So why couldn't the stronger Gaia hypotheses be more credible than otherwise - after all, how many episodes of crisis have been answered by the evolution of novel forms peculiarly capable of taking advantage of catastrophic conditions? And how many times has the sequel to catastrophe been something that looks like a return to a "happy medium" of environmental conditions that are friendly to one or another sympathetic kind of multicellular life?

This is where the strong Gaia hypotheses mates roughly with the real, enormous abyss of terrestrial time and the human teleological foreshortening of the evolutionary narrative.

Consider each of the biogenic catastrophes that Peter Ward mentions - how long did recovery from these catastrophes take, and, could we, if we discarded our anthropocentric, terrestrial blinders, actually call these "returns to a pleasant equilibria"?

Will Baird said...

Mr Greenbaum:

I am a bit confused here and it may be that I am simply too sleep deprived. My apologies ahead of my comment.

However, are you arguing in favor of a stronger Gaia Hypothesis or the Medea Hypothesis?

Ward states that despite recoveries from mass extinctions that the overall biomass of the planet has been declining since the Great Oxygenation Event and sped up since the Cambrian Explosion.

There are issues with the model that he's basing his book on. We'll get there, but not quite yet.

Mr. Greenbaum said...

Will, I'm not a strong Gaian.

Mr. Greenbaum said...

And, teleology is a dirty word in natural science.

Anonymous said...

Just to illuminate the discussion a bit further, the carbon cycle model on which Ward bases his discussion has no terms for non-continental surface biomass. In fact, there are no terms for any biological process other than a very basic productivity multiplier on continental area, which is modeled quite crudely (as a single value). All living matter is assumed to live on the continents -- perhaps a good first approximation today (but see Santelli 2008), but hardly useful for describing the Earth before life colonized the land.

The model is quite clearly a geophysical model with a perfunctory attempt to include a biosphere. It would perhaps be unfair to note that the original Franck et al. (2002) paper describing the model stated "the terrestrial biomass is greater the higher the atmospheric carbon dioxide content, the closer the surface temperature to its optimum value of 50 ◦C, and the larger the continental area," since the model was slightly revised in von Bloh et al. (2003) to allow for the possibility that entire kingdoms of organisms die at those temperatures.

It's very strange to base such a provocative biological hypothesis on this basically non-biological and oversimplified model. It immediately fails to convince.