Archive for November, 2010

Our final forum meeting held on November 19th focused on the topic of stochasticity in evolution, following the review by Lenormand et al.

Stochasticity can be divided into three categories: mutation, life history, and environmental stochasticity. While we have these categories, the primary question we ask is: what would happen if we could do it all over again? What would happen if we could press a “rerun” button?

Lucas presented three schools of thought in quantum mechanics for interpreting probabilistic indeterminancy. First is the school of thought that believes the universe is determinate, and we are temporarily ignorant. Second is that the universe is determinate and we are necessarily ignorant. Third is that the universe is indeterminate. We considered these schools of thought throughout our discussion of the different types of stochasticity and what falls into each of the three categories.

Returning to the idea of the “rerun” button, we asked: if we could duplicate the world in every respect at some point in time, would both of the worlds play out to the same result? This in turn leads to the question of how similar is similar? Do the two worlds have to be identical? Or if one plays out to an endpoint that is “similar” to the other, where do we draw the line of how “similar” they have to be to make it significant? We considered that perhaps it could be significant enough as long as the two worlds weren’t wildly different. However, this also raises the issue of time scale, particularly how long would we let the two worlds develop before we ask whether they are similar or not?

This led into a discussion of niches that exist in our world today. Oftentimes, similar niches in different parts of the world are filled by different organisms. A prime example is the woodpecker niche that is filled by the aye-aye in Madagascar. The aye-aye uses its thin, specialized middle finger to extract insects from within wood. In this instance, an organism evolved to fill the niche, yet in some parts of the world, the woodpecker niche exists even though there is nothing to fill it. This leads into the consideration of the gravity of a niche, or, how necessary is it that a niche be filled? Are certain niches more important than others, or is the filling of niches merely a random walk across fitness space? And also, is there an intelligence niche?

Next, our conversation turned to the idea of total determinism versus stochasticity. Going back to the idea of “rerunning” the world, we are led to the question of convergence. In this, we ask how much does stochasticity matter? We considered this question as we then discussed how stochasticity enters evolution and what the consequences are.

The first category that was defined above is mutation stochasticity. This category includes which mutation event occurs and when, and also the waiting time to a given adaptive mutation. This can have some environment and life history influence, but is mainly grouped into the mutation category. Also included is the order of mutations, and the genetic background on which an adaptation appears, or genetic draft. Genetic draft, also termed hitchhiking, is when a mutation can increase in frequency based on the genes that it is linked to; what happens to the mutation is determined by what happens nearby.

The second category defined is life history stochasticity. This includes genetic drift, which was described as “getting hit by a bus despite good genes.” Essentially, drift is the change in allele frequency due to random sampling. The importance of genetic drift was discussed and considered to have a negligible effect when determining whether a neutral mutation becomes fixed. If one did not have a genetic background, drift would be important, but as it is, background overwhelms drift. An ensuing discussion focused on whether we should limit the definition of drift to how it appears in the Wright-Fisher model, which uses a Ne (effective population size) that has little evidence of being indicative of the actual population size. Other factors in the life history category include migration and accidental inbreeding and outcrossing.

The third category is environmental stochasticity. This includes macro sources such as abiotic and biotic influences, examples being asteroids and humans, respectively. It also includes the environment with regards to one’s own species and with other species. This also led to the consideration of contingency, or that c happens because b rather than a happens. Stochastic processes can have contingent inputs which is important when considering environmental factors. Additionally, we have a model that assumes the fitness space is “well-behaved” but the environment is constantly changing which should also be considered in terms of what determines a fitness space.

One point we should consider is that we make these distinctions between the three groups for our models, but these categorizations do not occur in real life. Our categories are artificial, but useful to make statements about stochasticity.

While the above three categories were suggested in the paper by Lenormand et al., we discussed whether we preferred these divisions or whether we would make our stochastic model using different ones. It was suggested that we instead make the three categories be suborganismic, organismic (what affects the individual), and superorganismic (what affects the population).

Lastly, we considered how the anthropic principle and how it relates to evolutionary biology is influenced by chaotic and stochastic mathematics. Conclusively, we lamented on the fairly recent conception of stochasticity and on the fact that it is most often taken for granted.


Post contributed by K.P.

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Determinism, and the threat from science against free will and moral responsibility.

What if social scientists become too good at their job? Most fields of science look for causal explanations of whatever they are studying.  But what if they are studying human behavior? Is free will and moral responsibility under threat from science?  Can all human actions be explained in a determinist fashion?

Milk yield in cows can be calculated using a regression model which takes into account a variety of causal factors:

milk yield = β + G +β0(grass quality) + β1(calfhood nurturing) + ε

Where beta is some baseline, G is the genetic effect size, grass quality and nurturing are environmental effects, and epsilon is the error term.  The more explanatory terms that are added, the smaller epsilon becomes.  Some believe that, with enough information, epsilon will go to zero.  Others believe that epsilon can include totally intrinsic stochasticity, not just measurement error.  What if one of these models is fitted to human behavior?  Will we one day be able to predict if individual X will commit a homicide?  Is the error due to our lack of complete understanding? Or could it be free will?

Interestingly enough, most social scientists do not agree with the idea of human behavior being entirely deterministic.

Views of Free Will


Free will and moral responsibility are compatible with determinism.  “An action is ‘free’ or ‘responsible’ as long as it is performed in a rational, controlled, and reason-responsive manner, and out of preferences that are somehow the acting agent’s own.  A scientific understanding of human action does not, or at least need not, threaten these requirements, as they do not involve alternative possibilities.”


People have completely free will and our ability to explain human action is limited.

Explanatory Incompatibilism

Causal explanations are different from explanations in terms of reasons or intentions.

Conditioned Free Will (Joanna’s view)

We act as we are conditioned to do, but we can willfully set out to modify our conditioning.  This is synonymous with a dog deciding to take himself to training school.  We recognize, based on a normative value system, that we would like to see different behavior in ourselves and set out to make small changes to alter our conditioning.  There is a battle between what the emotional mind and intellectual mind want.  Free will can be seen as the overriding of the emotional mind by the intellectual.


Most social scientists reject the deterministic threat from science because the social sciences have taken a probabilistic turn.  “To say that someone is likely to do something is not as potentially damning as saying they were determined to do it.”   There are two ways to approach probabilism, through objective probability or subjective probability.

Objective probability assumes that some processes are inherently indeterminable, and we therefore will never be able to predict outcomes with complete accuracy.  Subjective probability concludes that processes are, in fact, deterministic, we just don’t know enough yet to predict outcomes with complete accuracy and therefore use probability as a prediction tool.  Which way a social scientist leans, however, does not affect their approach to research—the two are observationally equivalent.  Whether you believe the die inherently has a 1 in 6 chance of landing 5 or assign a probability of 1 in 6 to landing 5 because we have not (or cannot) account for all deterministic factors…the die still has a 1 in 6 chance of landing 5.

But objective probabilism seems just as frightening from a moral standpoint as determinism.  How do you hold someone accountable for actions based on inherent randomness?  From this standpoint, science can no longer causally account for behavior at all…but free will still has no say.  Most social scientists look for a mix or compromise between complete determinism, complete objective probabilism, and the potential for free will.

Where to put the social sciences on John Haught’s explanatory hierarchy?

In the last forum, John Haught proposed an explanatory hierarchy of the meta/physical universe.

The majority of psychologists would reject anything relating to evolutionary explanations, arguing that the study of human behavior is above evolution.  Some would raise human sciences to the level of theology, some would drop it evolution, or even chemical.  Should they reside between evolution and theology?  Or perhaps we should introduce a movable level which can permeate the other levels?  This question remains unanswered.


Post contributed by L.B.

Lateness and awkward formatting contributed by admin.

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