RE: Improbable Mountains in the Landscape

A couple days back, Chris Nedin at Ediacaran posted an excellent blog discussing Richard Dawkins’ Mt. Improbable analogy. As a means of commenting, I had cut and pasted a copy with my thoughts interdispersed here - Improbable Mountains in the Landscape.

As shown in the the comments section of that blog, Chris subsequently provided clarification and comment as a followup.

As a re-comment followup, I have posted the below thoughts as a new blog. A new blog was required because what I lack in substance I try to makeup for in shear bulk.

Chris,

I enjoy reading your writing, and many thanks for the time spent clarifying your point at my blogsite. I sincerely appreciate your patience in talking me through the analogy and your perspective of it, but – I struggle still…


POINT 1
I’m still not quite grasping the implication of the peak as an evolutionary cause rather than its consequence – or, as guiding? Do you mean that because a peak ends at a tapered point it gives the erroneous impression that the adaptation (or, increased “allele concentration”) is being filtered, dwindled or refined to a single individual as opposed to merely becoming more prevalent in the population?

[When I referred to an “end point” in my initial comment, I meant the expression in a similar sense as that used by Payne (see your “Told ya so”) when he mentioned a “pre-existing evolutionary potential.” In other words, the idea of an organism approaching a wall or limit in its available genetic range or plasticity.]


My gut feeling is that you’re viewing allele concentration as increasing towards adaptation/specialization and therefore being better symbolized by an expansion or widening as oppose to a taper? Sort of like this image:

I realize that I’ve eliminated a dimension from the landscape in this crude sketch; however from this graphic I can see a couple or your points illustrated:
1- Fitness decreases as allele concentration increases
2- Novelty would arise from the Generalists
3- Generalists exhibit the most fitness

In addition, the “pit” could be visualized as the area beneath the slope of the allele frequency (increasing towards adaptation, as you suggest); and the “peak” would be found at the maximum of the allele concentration (at the widest/deepest point of the pit).

e.g.

Beyond the images being overly simplistic and rudimentary, if the above likenesses accurately depict the fundamentals of the “pit” analogy- in terms of process only, I would only disagree with you regarding the y-axis. (I’m sure you saw that one coming.)

As an alternative, if we flipped the y-axis upside and let it represent increasing fitness (currently it’s displaying the inverse of fitness “1/Fitness”) the following would occur:
1- Novelty would rise from small populations (less fitness)
2- The “peak” would represent greater levels of specialization
3- The greater levels of adaptation would be found in the most fit populations

Such an alternative version would be more to my liking.


POINT 2
I think our disagreement regarding the peak as being “stagnant” or required as a prerequisite for adaptation is more-or-less a difference in interpretation of the intent of Dawkins’ analogy. I’m viewing the peak as occupied by an organism/population struggling to adapt to a fluctuating environment but being handicapped by genotypes inherited from ancestral lineages - a balancing act between inheritance and current selective pressures.

The organism is “handicapped” because its ancestors had struggled with a past environment that would have been different than the current one; ecologically different as measured by degree – all ecosystems undergo transition; for example a Coastal Grassland typically transitions into Flatwoods. Yes, major extinction events and catastrophes occur (with dramatic effect, often testing the breaking point of plasticity), but in terms of probability and frequency these are second to more gradual (not “slow;” rather step-by-step) changes.

In this sense, there is no pre-existing environment towards which an organism strives, it works with what’s at hand, AND, when probability succeeds in achieving sufficient “allele concentrations” (achieved through a combination of inheritance and selective pressures, mutation, etc…) adaptation occurs. With this adaptation resources become more readily available and relative fitness improves; thereby increasing the probability of greater allele concentrations (positive phenotypes) in future generations – a positive feedback. (Don’t want to get off on a tangent here, but remember that most feedbacks have delays)

Fitness must be increasing on the above y-axis! Otherwise nothing (regardless of the process that brought it to existence) becomes fixed.


POINT 3
Last point, I promise - Acquisition and loss of alleles and/or phenotypes…

Firstly, let me reemphasize that I interpret the “peak” as being representative of any given organism’s (or population’s or species’) current state of existence; the total and complete sum of its current condition. I do not interpret the peak as perfection or as a driver; it’s just a place marker.

Secondly, let me restate that “Phenotypes are not pro-actively reduced to a vestigial state; rather they’re no longer actively maintained. There’s no longer a pressure for the original phenotype to be preserved.”

If there is no active reducing, and they’re no longer actively maintained, then there is little or no “dead allele weight” to serve as baggage. Active change (adaptation) in the presence of selective pressures (of any variety) requires energy expenditure; inactivity and stasis are a bargain by comparison.

For example: Going back to the two fish example; let’s sat that there are two fish, one with well formed, fully functional eyes, the other with poorly functioning eyes. Both fish reside in a dark cave environment that has been stable for a reasonable amount of time. But then, suddenly - the environment changes!

The water temperature rises by half of a degree – that’s substantial change in an aquatic environment!

How could either fish be said to carrying extra baggage or dead allele weight? Yes, the fish with full eyesight may now need to work towards thermal tolerance, but it doesn’t need to work towards blindness or eye loss! In fact, both fish will now need to move towards thermal tolerance and I’m willing to wager that they both are under other pressures as well. They may be “working towards” elongate tactile whiskers and improved lateral line systems; they may be “working towards” the ability to produce sound (grunting) to attract mates… There could be numerous adaptations that one or both fish are “working towards.”

From this example we could say, “Given the totality of the circumstance, I think the fish with poor eyesight is better adapted to the dark warm cave.”

We couldn’t say, “The fish with poor eyesight is more evolved.”

We couldn’t say, “The goal of the fish with functional eyes is to become blind.”

Most importantly, we couldn’t say, “The better adapted fish is at an evolutionary dead end - and is doomed.”

Improbable Mountains in the Landscape

Chris Nedin at Ediacaran posted an excellent blog discussing Richard Dawkins’ Mt. Improbable analogy. Below I have cut and pasted a copy with my thoughts interdispersed; for the purposes of commenting only. His text is in quotes.

"In the ongoing Adaptationist v. Pluralist debate, both sides agree on a surprising amount. Both sides agree that there is more to evolution than adaptation by natural selection. However, Adaptationist would argue that adaptation by natural selection is the most important, or even the overwhelming, evolutionary process, and that evolution can be described as climbing Mt. Improbable – with adaptation to environment similar to climbing a fitness landscape peak towards optimal fitness (but please note, never, ever, reaching the top!)"

This misses the mark somewhat, and I think there are a couple of flawed inferences that would benefit from a touch of clarification. Firstly, the mountain metaphor was (and is) intended as fortification against the argument from design; or contra spontaneous materialization of “fully formed” and/or “fully adapted” organisms. When referenced in debates such as that of the “Adaptationist v. Pluralist” it can also be interpreted as being oppositional to radical saltations and other major macromutations of behavior or morphology that would result in the instantaneous generation of novel adaptations, or even a new species – such as making the leap from an individual amphibian to a reptile in a single birthing episode. In terms of fitness landscapes- peaks and mountains are only informative with respect to local genotypic values; in this way the analogy can be seen as limiting to lateral jumps between said peaks. In either the design or anti-saltation interpretations, Mt. Improbable certainly isn’t proposed as a formal hypothesis or mathematical model; it’s proposed as a mental tool to assist the lay science reader and general population in understanding the fundamental idea of change through time.

Mt. Improbable’s “peak” isn’t equivalent to “optimal fitness” or “adaptive perfection.” Indeed, adaptive perfection doesn’t exist, nor would Dawkins propose that it does; natural selection is only capable of providing a “better” solution, not a “best” solution. The mountain’s peak represents the current state and condition (inclusive of fitness) of any given organism, which when viewed from afar gives the FALSE appearance of being optimal, designed or perfectly adapted. From this point of view Mt. Improbable doesn’t detail where an organism is going or to what environmental factors it’s trying to adapt; instead it explains how the organism reached it’s current circumstance (i.e. gradually, not in a single giant leap).

The steady incline located on the opposite side of Mt. Improbable is the antithesis of a sheer cliff or rock face that would necessitate assistance from an external source or some other highly statistically unlikely event (i.e. improbable) in order to surmount or obtain it (“it,” being the before mentioned current condition). In this sense, the analogy of “climbing” wasn’t meant to represent a movement towards increased complexity, optimum fitness or some ideal form, but rather it was intended as a model for step-by-step, gradual processes in which leaps, jumps and major saltations are avoided. [To be clear - “gradual” used in this way doesn’t imply “slow,” or imperceptibly minute as may be interpreted during common use, but instead it means “graduated” as in stepwise or measured – not “slow change” but “bit-by-bit” by degrees of change.]

Regarding the statement, “but please note, never, ever, reaching the top!” – Of course it can’t be reached; as described above, a “better” solution (or increased fitness) is the only option. That said, some highly specialized organisms do get really close to the “end point” of their available genetic variation, when this occurs either the environment changes and they move in a different direction (up or down whatever mountain on which they happen to reside), or they enter a period of stasis (during stasis allele frequencies do change, but selection pressure isn’t sufficient to drive novel adaptations).

"I disagree. I think genetic drift accounts for most of the evolution that occurs, and natural selection, while very important – especially in creating diversity – accounts for a smaller percentage. However, both have worked together to produce the diversity of life on Earth."

Genetic drift absolutely serves as a source of variation within populations, and it may lead to adaptations, BUT in order for that variation or adaptation to become fixed in any meaningful way we need natural selection.

"I also have a problem with the Mt Improbable analogy . . . well, actually I have two problems.1) It perpetuates the idea that evolution is an upward striving process, and that derived or adapted groups are higher, than the less derived or less adapted and, as a consequence, fitter, advanced . . .better. (the old Tree of Life analogy problem.)"

There’s a key concept being missed here. The Mt. Improbable analogy does not, and is not intended to, predict or delineate evolutionary drivers, pressures or goals. Nor does it create a continuum of higher or lesser organisms. Its perspective is from the rearview mirror, it looks backwards in time.

Question: How did this organism reach such a state of seemingly perfect environmental synchrony?

Mt. Improbable’s Answer: Through a gradual bit-by-bit process, not in a single saltation.

Furthermore, the analogy doesn’t attempt to rank or compare the vastness of the Earth’s biota; it doesn’t establish a scale in order to weigh relative fitness or adaptation between individuals or species. It’s one critter atop the mount looking backwards though ancestral lineages.

"OK, maybe it is applicable to a fitness landscape, but there is no reason that the landscape has to have the peaks pointing upwards, . . . is there? Surely it's the distance between where you are on the peak and the schmucks on the fitness plane that is important, not the direction of that distance?"

No, there isn’t any particular reason why an upward rising mountain needs to be called into play in order for this concept to be understood. However neutral language does not lend itself to memorable metaphors; simplicity, clarity and fit are far more important. If envisioning an organism gazing up from a pit is more appealing than is considering one peering from a peak, then by all means…

Unless our goal is to create an artificial value system to scale and rank levels of fitness between unrelated organisms, the inter-schmuck distances and movements (upwards or downwards) seem irrelevant.

"Plus, fitness landscapes, are not permanent, or even solid. They change with the environment. A population/species, or whatever, may be quite "high" (see how hard it is to use neutral language)on a fitness peak one minute, and find itself down on the plane, or even in a fitness trough, with hardly any change in allele frequency, but a significant change in environment. In other words the fitness landscape moved underneath it."

Unless someone is implying that landscapes, environmental conditions, allele frequencies, selective pressures or any other biologic variables are static and non-dynamic - this almost seems a non sequitur. Of course, everything is in a state of flux; does the mountain analogy suggest stagnation of ecology?

"2) The real problem with the Mt Improbable analogy though, is that it gives the impression that as hard as it is to ‘climb up’ (and it is), the analogy suggests that it is relatively easier to ‘climb down’ - and it isn’t because its actually harder. OK that might be pushing the analogy a bit far – but that’s the point, it doesn’t hold up to detailed scrutiny."

It’s an analogy used to paint a picture of a basic premise. “Hard” climbing is in the eye of the beholder; a movement “up” or “down” requires the same amount of expenditure and neither direction denotes relative superiority.

"The real problem is that adaptation, in the broader picture, is an evolutionary cul-de-sac."

Quite the contrary, adaptation is antithetical to a “dead end” – Show me a successful lineage of organisms and I’ll show you an adaptation!

"Adaptation means that certain alleles are being selected for because they confer an advantage in a particular environment. If the environment changes, then the alleles that conferred an advantage may no longer do so. Worse, the very process of selecting for certain alleles may well have stopped other alleles getting fixed through drift – alleles which might be beneficial in the new environment. Even worse, the alleles that were originally selected for may be costly to produce and maintain where they confer no advantage, and thus be deleterious."

Does this imply, or openly state, that adaptation prevents and/or hinders biological evolution?

"But the really bad thing is that, as hard as it is to gain the alleles that provided an advantage, it is even harder to loose them, as this would require specific mutations to affect those particular alleles (rather than the random process that produced them). You could reduce them to a vestigial level, provided you survived long enough to do so. Difficult though, if you are struggling to survive in a new environment where the competition does not have the adaptive dead weight (unless you have some other advantage.)"

Phenotypes are not pro-actively reduced to a vestigial state; rather they’re no longer actively maintained. There’s no longer a pressure for the original phenotype to be preserved.

Once again, this would occur in a gradual manner (up or down directionality is irrelevant): If a species of fish finds itself in a dark cave portions of its anatomy supporting eyesight may no longer be positively selected. Overtime, sub-portions of this vision complex may undergo mutation, or be selected for another biological function. This may result in a slow degeneration of the complex through time. The eye will not disappear in its entirety overnight – it will be phased out. This however says nothing about complexity or the direction of evolution; the fish isn’t “more evolved” it’s better adapted to a given environment.

"The more adapted a group becomes, the more imbedded it is in a particular environment, and the more sensitive it is to changes to that environment."

Yes! This is the keystone of resource conservation – Save the Environment!

"Eventually all strategies lead to extinction, but during environmental change, it’s the generalists that survive, not the specialists. Adaptation generally leads to extinction. Highly adapted groups/species and ecosystems delicately balanced on a web of interconnected adaptations, will crash once environments change."

Seems a bit redundant here, everything leads to extinction + adaptation leads to extinction. My understanding is that some strategies improve fitness; others do indeed lead to extinction. And, generalists sometimes go extinct; specialists sometimes survive an environmental change.

Ecosystem’s “crash” is relative to which organisms are becoming extinct and which are becoming more specialized (adapted) to use (or better use) what resources remain.

"Adaptation is not climbing up Mt Improbable, it’s climbing down Pit Improbable!The pits are hard to find, but once in, it’s easier to go down than it is to back out, and if you adapt too far, you are trapped in a cul-de-sac with no way out when the environment changes. The generalists that flirt with the rim of the pit, or on the fitness plane have a better chance of surviving to become the stem stock for new adaptations. "

"It may well be that some species or groups of species in a pit break through to new fitness landscapes and produce new groups (e.g. birds and mammals from reptiles) because fitness landscapes are not flat, but curved.But for most populations/species, adaptation is a pit of no return."

Speciation, radiation, variety and biodiversity represent the consequences of specialization regardless of the drivers that push them to existence. “Ultimate survival” is a test to which we are all doomed to fail; however local survival in a given habitat, microhabitat or niche can be achieved and, in fact, is achieved more frequently than one should expect mathematically. This, in its majority, is due to specialization. From hyperthermophiles to lemurs – it’s adaptation that pushes life to the extremes, providing opportunity and prospect to the full range of creatures on the planet today. As the world’s climates continue to change, adaptation to the Arctic environment may eventually remove polar bears from existence; however it’s that same specialization and adaptation that put them there in the first place.


PS- It has just been pointed out to me that the Mt Improbable analogy was blogged (back in July) by Larry Moran at Sandwalk; with a counter argument by Jason Rosenhouse from EvolutionBlog.