role of behavior in evolution 1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

ROLE OF BEHAVIORAL SHIFT IN EVOLUTION


Behavioral traits are reversible, expressed in response to an internal or external cue (Fig. 2A). Without the cue, a particular behavior is not perceptible (e.g., parental behavior in the absence of offspring).

Morphology is relatively stable in adults because, in most cases, it is not immediately reactive to a cue except during ontogeny (West-Eberhard 2003).


A behavioral shift

Occur faster than an adaptive change in morphology or physiology and thus should take the lead in evolution


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Fig. 2 REACTIVITY VS PLASTICITY in the level of expression of behavior(LEB) within an individual.

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In (A), the LEB is highly consistent within as well as across environmental contexts (indicated by white and gray areas). Reactivity of behavior is indicated by the response of behavior to a cue (arrows) that can be either an internal or external signal.

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In (B), the LEB is not affected by environmental context, but does change over time.

This can be due to habituation, learning, or age-dependent life history strategies.

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In (C), the LEB is highly consistent within contexts, but changes between contexts. An example is the expression of parental behavior in the presence or absence of a nest predator.

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(D), the LEB is consistent toward a specific cue, but Changes when the cue changes (black arrows).In this case, the change in expression may indicate two functionally different behaviors (e.g conspecific vs heterospecific aggression).

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All these illustrate a situation in which behavioral plasticity is limited in some way, yet, in each scenario it is still possible that expression of behavior is also developmentally plastic if it was modified during ontogeny by environmental context.

Thus, more complex shifts in the level of expression or reactivity of behavior due to different combinations of developmental plasticity, behavioral flexibility, and learning are also possible


Constructing A Unified Framework, to combine both the Hypotheses1. Behavior as a Driver of Evolution2. Behavior as an Inhibitor of Evolution


The Two Opposing Hypotheses

Evolutionary Change

Evolutionary Stasis


Both propose that behaviors affect evolutionary processes by altering selection pressures (paths to and from 4a and paths to and from 5b). The gray boxes highlight two areas where mechanisms have not been made explicit

Evolutionary Change

Evolutionary Stasis


Fig. 3 Illustration of a unified framework, presenting Behavior as both a driver and inhibitor of evolution


In this conceptual diagram, a change in the environment precedes behavioral shifts.

• in Fig. 1 the paths linking behavioral shifts to evolutionary divergence and stasis occur as alternate pathways, here, they can occur simultaneously.


• For example, a behavioral shift leading to Box 3 can simultaneously cause and animal to experience novel selection on one trait (path from Box 3 to 5) while avoiding selection on another (path from Box 3 to 6).


Gray arrows indicate continuation of paths originating from Box 4. Shifts that cause a move to a new environment (Box 2–4) are unique in that novel selection pressures are not necessary for evolutionary divergence.


The black arrows indicate potential feedback loops between environmental and behavioral changes


• The constraining influence of behavior has been put forward as an explanation for evolutionary stasis within lineages and niche conservatism within clades.

• Nonetheless, the hypothesis that behavioral change prevents natural selection from operating in new environments has never been experimentally tested.


Acceptance that behaviors are important in evolution in current evolutionary theory is apparent from the Recognition that behavior can affect evolutionary change is evident in models which are the basis for population genetics, such as in the assumptions of Hardy-Weinberg


Hardy-Weinberg rule, the equilibrium of genotypes over time

remains the same in a population as long as four conditions are met.

1.individuals must select mates randomly without regard to visible, or phenotypic, traits.

2.no genotype can be favored in such a way that it will increase in frequency in the population over time.


Hardy-Weinberg rule,3. No new alleles can be introduced into

the population, either by individuals from outside the population or by alleles that have changed, or mutated, from one form to another.

4. the number of individuals and genotypes in the population remain high.


Hardy-Weinberg rule,

1. Select mates randomly

Sexual selection is biased

3. absence of emigration and immigration

Animals do migrate

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Examples of Behavior and Morphology Evolving Synchronously

Showing that behavior is a driving force in evolution.

The color and mating behavior of male guppies reflect a balance between natural selection for obscure coloration and behavior versus sexual selection for conspicuous coloration and mating behavior (Endler 1992).


In the absence of predators, females prefer males with bright coloration and conspicuous displays; thus, behavioral drive by females controls the evolution of male traits in predator-free streams. However, when visually hunting predators the Pike Fishwere introduced, they attacked the most brightly colored and conspicuously displaying males. Thus, predators selected simultaneously on male color and behavior, and males quickly evolved muted colors and displays(Houde and Endler 1990).


The introduction of predators in turn led to a change in female preference against males with bright colors and conspicuous displays (Houde and Endler 1990). Thus, evolutionary changes in morphology (male coloration) and in behavior (male displays) apparently drove a correlated evolutionary change in behavior (female preference).

In this example, male morphology and behavior evolved in tandem, and both drove a correlated change in behavior (female preference).


Lactase in Adult humans:

Some human populations descended from cattle raising cultures provide a possible example of the power of behavior to drive the fixation of genes for lactose utilization. Most members of these populations (i.e., Northern European and some African populations) differ from other people and animals by possessing lactase in intestine as adults.


Lactase in Adult humans:

The enzyme is apparently the result of a regulatory mutation whose spread through these populations was fostered by the selection pressure imposed by a new culturally transmitted behavior-namely, the consumption of cows' milk by adults. This practice presumably began only after cattle were domesticated, about 10,000 years ago.


The High Rate of Anatomical Evolution in Birds and Mammals



• birds share with placental mammals the distinction of having had a high rate of anatomical evolution, compared to that in lower vertebrates.



• The rate appears to have been very high in songbirds and higher primates and extremely high in the genus Homo.


• In an attempt to explain such contrasts in rates of anatomical evolution, we advance the hypothesis that

• in higher vertebrates, behavior, rather than environmental change, is the major driving force for evolution at the organismal level.

• This hypothesis predicts accelerated anatomical evolution in species composed of numerous mobile individuals with the dual capacity for behavioral innovation and social propagation of new habits.


Consistent with this hypothesis, we demonstrate a correlation between relative brain size and rate of anatomical evolution.


Autocatalysis.• During the history of land vertebrates,

the relative size of the brain has increased in a manner that is reminiscent of an autocatalytic process in the lineages leading from amphibians through reptiles to birds and several mammalian groups, especially in the lineage leading to humans. In light of the strong correlation between relative brain size and rate of anatomical evolution, we propose that this rate has also been accelerating along those lineages


Autocatalysis.• During the history of land vertebrates,

the relative size of the brain has increased in a manner that is reminiscent of an autocatalytic process in the lineages leading from amphibians through reptiles to birds and several mammalian groups, especially in the lineage leading to humans


Our view of anatomical evolution as an autocatalytic process, mediated by social learning, contrasts with the old view that the pressure to evolve has been rather steady through geological time, owing to relentless environmental changes generated by constant geological forces.


The genus Homo is at the top of the scale in regard to rate of anatomical evolution, relative brain size, and the capacity for rapid behavioral shifts throughout large populations. From the strength of the correlation (r > 0.97) between the two sets of values in Table 4 we conclude that most of the variation in rate of anatomical evolution among vertebrates is associated with, and thus may be due to, variation in relative brain size.


Implicit in all of these concepts and models is an active organism—one that chooses where it will live and who it will mate with, and one that responds to changes in its environment.

The foundation for arguments that behavior plays a unique role in evolution—whether that role is as a driver or as an inhibitor —is that behavioral traits are distinct from other aspects of the phenotype .

Active organisms are shaped by their environment and these same organisms also shape heir environment

( Laland et al. 1999, 2000).


The challenge for future studies in this area is to determine how different types of behaviors (e.g., social behaviors versus habitat selection) and different types of behavioral shifts (e.g., shifts due to learning versus shifts due to selection) affect selection pressures in the short term to ultimately impact the rate of evolutionary diversification.


The theory of niche construction proposes a similar view of the active role of organisms in evolution.

Behavior plays a prominent role in the theory of niche construction and many of the examples used to illustrate niche construction are of behavioral traits (Odling-Smee et al. 2003, Chap. 2)


References• Raymond B. Huey,1,* Paul E. Hertz,2,† and B.

Sinervo( 2003)Behavioral Drive versus Behavioral Inertia in Evolution: A Null Model Approach the American Naturalist: Vol. 161, pp. 357–366.

• Jeff S. Wyles, Joseph G. Kunkelt, And Allan C. Wilson(1983) Birds, behavior, and anatomical evolution (rates of evolution/nongenetic propagation of new habits/brain size) Evolution: Vol. 80, pp. 4394-4397.

role of behavior in evolution 1

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