RUNNING HEAD: Human Adaptation to the Ancient World

RUNNING HEAD: Human Adaptation to the Ancient World

Critical Review of

Irons' Stance on Early Human Adaptation


Brianne VanElslander, Chris Murphy, Eric Culqui

Loyola Marymount University


Dr. M. Mills

Evolutionary Psychology

September 21, 2000



            The environment of evolutionary adaptation refers to our ancestors' physical surroundings, which presented survival and reproductive problems causing psychological mechanisms to be developed in order to address these problems.  William Irons, from the Department of Anthropology at Northwestern University, claims that the environment of evolutionary adaptation (EEA) is not limited to the Pleistocene foraging societies for several reasons: information on the number of generations required for evolutionary change holds that more generations than those in the Pleistocene foraging societies are needed to develop an adaptive trait, the types of cultural variation in contemporary and recent societies does not fair well with the notion that the EEA is limited to the Pleistocene foraging societies, and the best data Irons has on psychological mechanisms does not fit with the EEA being limited to the Pleistocene foraging societies.  This is contrary to previous theories suggested by scholars, such as Symons proposed in The Evolution of Human Sexuality (1989). Throughout Irons' piece studies of human affairs are explained in terms of psychological mechanisms.


The Environment of Evolutionary Adaptation


            Irons goes great lengths to refute the belief held by Symons (1989) of some cultural anthropologists and psychologists that human adaptation reached its pinnacle with the end of the Pleistocene. There are number of arguments used to support this stance. One is the fact that adaptations are created only in the specific environment in which the in which the organism lives in at the time of the adaptation.  Another is the fact that the Pleistocene environment is the only chronologically stable environment our species has known, having hosted us for 99% of our total time on Earth. While Irons does not refute this fact, he defends the position that human adaptation did not end with the end of the Pleistocene because the environment was not the catalyst for adaptation, but rather, other humans were and still are today.

            Irons supports the view that the major hostile force in any human environment, regardless of geography is other human beings. In the competition for valuable resources and mates, humans have learned to adapt to the physical and psychological tactics used by other humans to dominate the resources of particular area, or another human or group of humans. Irons states that these tactics involved intricate combinations of, "nepotism, direct reciprocity, and indirect reciprocity." (Irons, 1990). This then led to a "run-away" type of adaptation, as described by Alexander (Alexander1979;1987) that continued as more humans came about to interact with one another. Irons uses seven major arguments to support his position.

            First, Irons uses the evidence that behaviorally and neurologically modern humans probably did not appear until about 50,000 to 35,000 years ago, which is near the end of the Pleistocene. Paleontologists suggest that the humans dominant before that time, Homo erectus and archaic Homo sapiens did not have the biological components necessary for culture, as we would define it. The sudden appearance of modern Homo sapiens supports this run-away theory of adaptation mentioned earlier.

            Second, Irons offers the evidence that the environments of the late Pleistocene in which modern humans made their first appearance, were not stable. Not all human societies were nomadic hunting and gathering, and there was great variation including sedentary hunting and gathering and economic in nature.



Third, Irons goes on to state that in the 50,000-35,000 years since the end of the Pleistocene it is unlikely that there would be no human adaptation during that time. He estimates there are roughly 300 generations since the end of the Pleistocene and some adaptation, especially psychological would occur in that time, given his belief that humans are their own catalyst for adaptation.

            Fourth, Irons points out the fact that since the development of agriculture about 10,000 years ago, the human population has increased exponentially. This phenomenon does not accompany a species that has ceased to adapt or has taken on maladaptive behaviors. If humans had stopped developing adaptive behavior, or had only done achieved this randomly, we would not be around today.

            Fifth, the majority of data on psychological mechanisms indicates that we are best adapted to dealing with other people rather than environmental adaptations.

            Sixth, in traditional societies, culturally defined goals correlate more consistently with reproductive success. The adherence to cultural norms and accepted goals such as allocation of resources, physical fitness, and others contributes greatly to obtaining a mate and producing offspring. This tendency is also present in industrial and urban societies, but is less defined. Also, evidence suggests that more traditional societies provide settings close enough to those of evolution so as to cause psychological adaptations to produce adaptive effects.

            Seventh, in relation to his sixth argument, Irons points out how cultural goals are subjective in nature and how this subjectivity is directly related to the environment in which the culture exists. In agrarian societies, accumulation of land, produce, and livestock would constitute cultural goals and almost insure mate acquirement, reproductive success, and social status and acceptance. By contrast, in a hunting gathering society, the success on the hunt would be the cultural goal. In a war state, the goal of violent victories over competitors may be the cultural goal. This also contributes to the variance in mating arrangements according to culture. Polyandry may work better in some environments better than monogamy or some other mating arrangement and vice versa.


An Alternate View of the Appearance and Disappearance of the EEA



In this section Irons proposes that Alexander's theory of the process of run away selection could possibly explain the rapid emergence of behaviorally modern people during a time of no new transformation in the physical environment.  He claims that people have not undergone any dramatic change since the appearance of Homo sapiens 50,000-35,000 years ago.  Until very recently most of our psychological mechanisms worked well enough to be maintained by stabilizing selection for most nonurban, nonindustrial societies (Irons, 1990).  While the decline in fertility related to the demographic transition goes back up to six generations for some populations it has not even occurred in others. It is probable that six generations is not enough time for the adaptation to be disturbed by mutation and drift, or possibly altered by new directional selection.  It is even less plausible that an adaptation that did not present a reproductive advantage would remain intact for hundreds of generations.  This hypothesis suggests that our EEA began very late in the Pleistocene and extended for many up to about two hundred years ago and for others up to the present day but it is difficult to test. 



Many evolutionary anthropologists and psychologists like Symons see populations as stably adapted to a foraging way of life for most of the Pleistocene followed by ten thousand years of environmental novelty (Irons, 1990).  This view is also difficult to test and has just as much speculation in it as the previous one.  Another view is that the environmental uniqueness that could have disrupted adaptations first appeared with urbanization. It is probably a better idea to think in terms of many events occurring, each of which disrupted parts of our environment and left part of the world's population a little less well adapted to the current environment.

Irons disagrees with Symons idea that measurements of reproductive consequences in societies tell us nothing.  He claims that while his view of the EEA may not be correct, it still holds the empirical evidence that Symons lacks.  He agrees with Turk in that determining reproductive consequences is a good way to establish which elements in the environment people evolved to respond to and also how they evolved to respond to them.  This, in addition to good empirical evidence and theory on the EEA can help us comprehend the underlying psychological mechanisms.   He believes that an empirical investigation of vasectomy, birth control pills and other forms of contraception may help us discover something about the human psyche but is not likely to lead us to believe that these played a major role in eliminating the EEA.

Symons is confident that post Pleistocene environments change the effect of psychological mechanisms on reproduction, but that the mechanisms themselves are "innate" and not confounded by unique conditions (Irons, 1990).  Irons disagrees and assumes that we can't really determine if novelty disrupts adaptations by distorting psychological mechanisms or reproductive consequence but there is no reason to assume that we should not use our knowledge of evolution to figure out what is going on.


Specialized Psychological Mechanisms


Even though Irons disagrees with Symons on the above issues he agrees with many of his ideas on psychological mechanisms and his notion that we have a fixed emotional and motivational structure, but with less specificity.  He states that while we have far different criteria for choosing a mate and choosing a meal we still use some form of specialized decision-making and weigh out our consequences.  Our vast array of psychological mechanisms include very specialized ones and very general ones.  However, even the most general mechanism is not that general.


Future Research Strategies


Irons has one fundamental belief about the Evolutionary Environment of Adaptation and that is by combining many lines of inquiry we will have a more solid evolutionary science.  He says we should combine the study of psychological mechanisms with many other lines of study.  Even neuroscience will eventually have something to tell us.  While it would be impossible to incorporate all these topics at once in every investigation researchers can be aware of what is going on in other areas of specialization.  By doing this we will achieve what we essentially need which is a broader perspective.



Works Cited

            Irons, W. (1990). Let's make our perspective broader rather than narrower. A comment on Turke's "Which humans behave adaptively, and why does it matter?" and on the so-called DA-DP debate. Ethology and Sociobiology II, 361-374

The Human Ancestral Environment

Brianne VanElslander, Chris Murphy, and Eric Culqui


I.  Environment of Evolutionary Adaptation

            A.  Not limited to the Pleistocene foraging societies

1.      Behaviorally and neurologically modern people did not appear until   

       about 50,000-35,000 years ago

                                    a.  First evidence of art, ritual, and religion

                        2.  The environments of the late Pleistocene were not stable

                                    a.  Variations between environments and local cultures

3.      Our psychological mechanisms were not likely to have remained static after 300 generations in environments in which they do not  

produce adaptive effects

                        4.  The world's human population grew after the origin of agriculture

                                    a.  Population eventually increased a hundredfold

5.      Human psyches are adapted to dealing with other people more than other elements of the environments

                                    a.  Other human groups were a major hostile force of nature

                                    b.  Allows inter-group relationship improvements

6.      Culturally defined goals consistently correlate with reproductive success in more traditional societies

7.      Cultural goals associated with reproductive success vary between societies

            B.  Alternate view of the appearance and disappearance of the EEA

            C.  Specialized psychological mechanisms

                        1.  example- people have propensity to imitate success and anti imitate                                failure

                                          - choices of food and mates

            D.  Future research strategies

                        1.  Combination of many lines of study

                                    a.  Psychological mechanisms, with empirical study of exact nature                                      of the EEA, with demographic measures of reproductive       

                                         consequences of behavior, etc.


Critical Review Items



 A.)  Four Interesting or Informative Points Made by the Author:


        The Environment of Evolutionary Adaptation is not limited to the Pleistocene foraging societies.

        After the appearance of agriculture the population increased one hundred fold indicating that maladaptive behavior does not produce population growth.

        One of the major influences in the adaptation of the human mind was the interaction between other people rather than the environment.

        Like Darwin, Irons holds the fundamental belief that by combining many lines of inquiry relating to the Environment of Evolutionary Adaptation we will have a more solid evolutionary science.



B.)   Two Arguments Made by the Author that the Panel Disagreed With and/or Required                Further Explanation:        


        Irons mentions that environments of the late Pleistocene were not stable and may have been a greater variation in human cultures but he offers no evidence to support this.

        Irons suggests that the Environment of Evolutionary Adaptation began very late in the Pleistocene and extended for many up to about to hundred years ago and for others up to the present day but he has no way of empirically testing this hypothesis.



C.) Three Concepts the Panel Had Questions About or Required Further Explanation:


        Specifically, how do the contemporary traditional societies differ from those of the Pleistocene?

        Which elements of the environment are relevant to the operation of our psyches and how have these elements changed?

        What were the hostile forces that the human mind evolved to cope with and how have these changed since the appearance of modern sapiens?