Friday, January 16, 2009

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.


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…

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).


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.

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.

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.”


  1. Hi Johnny,

    Thanks again for the comments. They have been really useful as I consolidate my thoughts on this issue.

    I have a new post here, but I'll just comment on your points.

    Point 1
    Shape really isn't an issue. Actually the peak should expand as the population becomes more successful.

    Both the peak and pit represent the highest concentration of beneficial alleles and, of course they can be the source of new populations and species - especially in the environment that they are better adapted to. So in that sense there is little difference between a peak or a pit.

    But . . .

    Point 2
    Yes, the population occupies the peak. It does from the start. As the beneficial allele frequency increases due to reproductive success the peak rises away from the 'normal' distribution. But that is the point. If the population occupies the peak from the start and the 'hight' of the peak increases as a function of the beneficial allele frequency - there is no climbing involved!

    On the last paragraph - in my new post I indicate that the way I look at landscapes (topographies) fitness increases result in pits, but that pit is 90 degrees to the landscape and the landscape can be in any orientation. Also alleles can be fixed in the population without an adaptation - genetic drift. In my scenario this occurs when the pit cause by the ew allele is broad and shallow and the allele spreads quickly through the population resulting in topography 'bounce', but no deep pit. Mt Improbable can't account for genetic drift, but then it wasn't supposed to.

    Point 3
    I disagree that there would be no dead allele weight to act as baggage. If the previously beneficial alleles caused some feature that is energetically expensive to form and or maintain, then the organism is at a disadvantage because it has to expend energy/resources to maintain something that is no longer paying off for it. Other organisms without the expensive add-on make better use of available energy and hence have an advantage - a small one to be sure, but every little helps!



    We’re getting closer… I think that I may have “read into” your initial Improbable post a little too deeply… To me, this update seems somewhat of a turnaround from the first in that it moves away from the literary argument of a Mt. Improbable as “bad analogy” and instead states “And a good job it does.” I find it much more agreeable. Furthermore, it now seems more apparent that the “pit” analogy is designed so that “we can formulate an analogy that can be expanded to encompass more of the evolution process.”

    Since we agree that Mt. Improbable is a good analogy for its intended purpose, I’ll move on.

    Viewing the two blog post here, as well as the two comments you were kind enough to provide to the “rebuttals” at my site, I think that, broadly speaking, there are a couple of assumptions or implications being made that are fundamentally false – false, based on my understanding.

    1. You describe Natural Selection as acquiring beneficial alleles through a “random process.” This is incorrect; NS is a non-random cumulative process.

    2. You imply that genetic drift contributes to fitness when, in fact, drift is a random process that is entirely disconnected from fitness. (Big point)

    3. Through descriptions of lateral jumps between peaks, distances between pits and by suggesting that new “groups” can arise by “breaking through new fitness landscapes,” you’re implying that a Genus, Class or Family can erupt from a Species. This is false. Species rise from “speciation” at the species level. There is no jumping between points – only steps - a continuous gradation

    4. You imply that “Generalist” and “Specialist” are definitive forms by saying that one has survival value over the other. These are relative terms. You may view/classify a particular insectivorous mammal as a specialist because its diet is limited to only insects – I could counter by saying that it’s a generalist because it eats a wide variety of insects as oppose to limiting its consumption to termites. Without knowing the type and extent of a theoretical catastrophe – there is absolutely no way to predict what niches will remain intact or the rate to which any event survivors will rebound.

    5. You create a false dichotomy between peaks and pits; both are landscapes and as the term “landscape” suggests, both represent a varied ever changing state complete with valleys, ridges, prairies, bumps, holes – they are one in the same –metaphors for change.

    6. You imply that organisms adapt or imbed themselves into a static environment, when in fact static environments don’t exist. Ecology is a balancing act, therefore so is adaptation.

    7. When comparing short-term success with long-term survival you seem to suggest that evolution is a fundamentally different process following some catastrophe or major ecological shift. This isn’t so; the same processes driving speciation, drift and natural selection today are the very same processes that will drive evolution following an asteroid impact. If adaptation and specialization are what is successful in the here-and-now, they are also going to be successful strategies following a catastrophe.

    8. Describing both Natural Selection and Drift in terms of allele frequency is fine; however keep in mind that NS works with phenotypes as well as genotypes; this builds the link to fitness. Drift does not have this link.

    9. The idea that a current level of adaptation exhibited by an organism somehow reflects its future potential or its available genetic plasticity is erroneous.

    However, I do admit, the visual image of a “sag” being created by the weight of an area with increased allele concentration is pretty catchy…

    In closing, I fully admit to being more-or-less a proponent of the adaptationist side of the house and it isn’t my intent to wear out my welcome. Although I express contrary views, I do it only because I feel there is a worthwhile discussion to be had and because you present the “other side” very well.