Darwinian evolution is the idea that all the varieties of life on earth are related, having descended by a process of gradual and cumulative modification from a single common ancestor. An important driving process of this modification is natural selection, described in my earlier post entitled An Evolutionary View of Emotions. Note that I have emphasised the words gradual and cumulative. A common criticism of Darwinian evolution is that the probability of any complex biological structure, whether it be an eye, a wing, or the brain assembling itself by chance (without the guidance of some supernatural creator) is so incredibly small as to be, for all practical purposes, impossible. It has been equated to the probability of a hurricane sweeping through a junkyard and assembling a Boeing 747 out of the scrap metal (Dawkins, 2006).
This criticism betrays a strong misconception about the evolutionary process. Complex biological structures DO NOT suddenly spring into being by chance. The notion that an eyeless organism would give birth to an offspring with a fully-functioning pair of eyes is absolutely ludicrous. The eye, like any other structure that has evolved by Darwinian evolution has done so by a gradual and cumulative process of selection. When previous designs are modified in very slight ways that provide an organism with some type of advantage, however slight, the modified designs are preserved and becoming more prevalent in future generations. In the often cut-throat natural world, even very slight advantages to an organism can prove telling in the evolutionary struggle. While the probability of a complex biological structure suddenly springing into being as a functioning whole may be effectively zero, the probabilities of the much smaller individual modifications that will accumulate over time, leading to the fully functioning structure are much, much higher. A metaphor for natural selection used by the British zoologist Richard Dawkins is that of a mountain – Mount Improbable:
"Mount Improbable rears up from the plain, lofting its peaks dizzily to the rarefied sky. The towering, vertical cliffs of Mount Improbable can never, it seems, be climbed. Dwarfed like insects, thwarted mountaineers crawl and scrabble along the foot, gazing hopelessly at the sheer, unattainable heights. They shake their tiny, baffled heads and declare the brooding summit forever unscalable." (Dawkins, 1996, p. 64)
The peaks of Mount Improbable stand for evolution’s most complex achievements such as the eye, or the human brain. However, as Dawkins continues:
"Our mountaineers are too ambitious. So intent are they on the perpendicular drama of the cliffs, they do not think to look around the other side of the mountain. There they would find not vertical cliffs and echoing canyons, but gently inclined grassy meadows, graded steadily and easily towards the distant uplands. Occasionally the gradual ascent is punctuated by a small, rocky crag, but you can usually find a detour that is not too steep for a fit hill-walker in stout shoes and with time to spare. The sheer height of the peak doesn’t matter as long as you don’t try to scale it in a single bound. Locate the mildly sloping path and, if you have unlimited time, the ascent is only as formidable as the next step." (Dawkins, 1996, p. 64)
Another criticism leveled at Darwinian evolution at this point is that an eye is a very complex structure. For example, it has a focusing lens and a light sensitive screen positioned just at the focal plane of the lens, and an iris that contracts and expands to let in just the right amount of light. If some or all of the parts arranged in a seemingly delicate balance were not in place, the eye would not be able to function properly and therefore would not be of any advantage to its bearer. So how could a complex biological structure such as an eye evolve by cumulative modification? A more concise way of putting this argument is “What good is half an eye?”
As I noted before, in the cut-throat natural world even very slight advantages to an organism can prove telling in evolution. In the case of the eye, an eyeless ancestor could have been born with a bit of skin that happened to be a bit more sensitive to light than normal. All skin is slightly sensitive to light anyway (Evans & Zarate, 1999). This slight modification would have enabled its bearer to detect the shadow of a predator slightly quicker than its siblings and therefore improve its chances of escape and survival ever so slightly, allowing natural selection to occur (Evans & Zarate, 1999). Further slight modifications continued to accumulate until eventually we had a complete eye. This short essay is meant simply as an introduction to the idea of cumulative selection. For those readers that are interested in reading further, I refer you to Richard Dawkins’ wonderful book, Climbing Mount Improbable, which goes into much greater detail about the evolution of the eye. I also include a link here to a video of a lecture given by Dawkins on the topic of cumulative selection.
The evolution of complex biological structures by natural selection is a gradual process which may take millions of years. Part of the reason for this is that natural selection can only act upon the phenotypic variation that is already present in a population. An important source of this variation is mutation.
As noted in my earlier post entitled An Evolutionary View of Emotions, one of the conditions that need to be met in order for natural selection to occur is that phenotypic (physiological, anatomical or behavioural) variation must be able to be fairly reliably passed from parent to offspring. In Charles Darwin’s day people were aware that children tend to resemble their parents in certain characteristics, but the actual mechanism by which these characteristics were passed from parent to offspring was unknown. Nowadays we know that genes are the agents by which this variation is fairly reliably passed from parent to offspring. A gene contains instructions vital to the development of a particular characteristic. These instructions are in the form of a universal code of bases called DNA that is present in all living organisms. This code needs to be copied and then passed onto the offspring during reproduction. Occasionally random copying errors are made. These copying errors are mutations. Most mutations are either inconsequential or are harmful to the individual’s chances of surviving and reproducing. If a mutation is harmful, then typically the gene containing that mutation is not passed on to offspring and is therefore not present in future generations. But very occasionally a mutation will cause a change in the phenotype of an individual that will prove beneficial (however slightly). Because mutations are uncommon, beneficial mutations much more so, the evolutionary process is typically very slow.
Evolutionary psychologists argue that the human brain is the product of a long period of evolution in much the same way as an eye or wing. Fitness-enhancing modifications to the brain’s information processing mechanisms have been preserved and accumulated over the course of millions of years (Buller, 2005). As noted in an earlier post, an organism’s fitness is largely dependent on how well adapted its characteristics are to the demands or pressures of the environment it inhabits. These “selection pressures” can be thought of as adaptive problems. So the brain must have been “designed” by selection to produce behavioural solutions to adaptive problems faced by human populations.
The slow nature of the evolutionary process leads us to one of the key theoretical assumptions of the paradigm of evolutionary psychology associated with Tooby, Cosmides, Buss and others. Because cultural and technological evolution occurs much faster than biological evolution, our minds are adapted to a very different environment than the one we inhabit today. Evidence of settled agrarian (agriculture-based) cultures is only evident from around 11,000 years ago. This is a blink of an eye in evolutionary time. For about 95% of the last two million years of our species evolution, a period of time referred to as the Pleistocene, early humans – our ancestors – would have been living a nomadic hunter-gatherer lifestyle in tribal groups in the savannah plains of southern and eastern Africa (Fletcher, 2002). Fossil evidence indicates that the ancestors of humans originated in Africa (Campbell et al., 2008). Evolutionary psychologists argue that natural selection has shaped our minds to the demands of this life-style with no major changes to our psychology in response to the significant cultural and technological advances since the Pleistocene because 11,000 years is nowhere near long enough for significant evolutionary change to take place. To put it another way – “our modern skulls house a Stone Age mind!” (Buller, 2005)
I have already noted one apparent piece of evidence for this theoretical assumption in an earlier post on this blog (An Evolutionary View of Emotions) – the strong tendency for humans to develop a fear of snakes. A fear of snakes remains by far one of the most common fears that people the world over exhibit, even in places where the only contact that people have with snakes is in very safe, controlled environments such as zoos and wildlife parks. Evolutionary psychologists argue that this is because poisonous snakes were a major threat to our hunter-gatherer ancestors in the African savannah, and the tendency to develop a fear of snakes was the evolved “solution” to the adaptive problem of avoiding this potential danger. A continued pre-disposition towards snake phobias, even in places where we are unlikely to face a threat from poisonous snakes, is a result of this Pleistocene “evolutionary strategy” to avoid potentially dangerous snakes.
From an evolutionary perspective (that is, thinking in terms of what will improve the odds of survival), wouldn’t it make more sense if people that lived in large urban areas were born with a biological predisposition to develop a fear of motor vehicles? After all, in these areas being hit by a car is a more likely way of getting yourself killed than being bitten by a poisonous snake. Yet, for humans in all walks of life, it is much easier to develop a fear of snakes or spiders than cars. Evolutionary psychologists would argue that because motor vehicles were only invented a little over 100 years ago – roughly four generations ago – such a biological predisposition would not have had anywhere near enough time to evolve by natural selection.
A common argument against evolutionary psychology is that if the aim of life is to (survive and) reproduce, why do so many people use contraception during sex. This argument betrays a common misunderstanding about evolutionary psychology. Natural selection has NOT resulted in a conscious motive to have children. Evolution has instead made sex desirable and rewarding because it is through this behaviour that we reproduce. People generally enjoy sex, but don’t necessarily want children. Also, reliable contraception is a development of the last few decades. As a result, we are now generally able to separate the act of sex from reproduction fairly reliably, unlike our Pleistocene ancestors. This hasn’t had any effect on our evolution-installed desire for sex, with or without a condom. As would be predicted from an evolutionary psychology perspective, the very recently acquired ability to separate the act of sex from reproduction has not changed our underlying psychology.
According to an evolutionary hypothesis, referred to as Parental Investment theory, in any species, the sex that invests more in offspring (generally the female) will evolve to be more choosy about mating, while the sex that invests less in offspring will evolve to be more competitive with other members of their own sex for sexual access to the valuable, high investing opposite sex (Buss, 1995). In the case of humans, like all other mammal species, the female is the high-investing sex. The minimum obligatory investment for a female during reproduction is nine months of pregnancy. Estimates tend to vary (depending on who you ask!) about the minimum obligatory investment by males, but post-coital investment is not required by males. Research supports Parental Investment theory (see Fletcher, 2002). In one famous experiment, the experimenters had attractive confederates approached members of the opposite sex on the University of Hawaii campus and asked them if they wanted to have sex. More than seventy percent of males said yes, but not one of the females did! What’s more, most of the males that turned down the offer apologized to the female confederate and explained themselves by saying they were married or already involved with someone else, whereas most of the females responded with outrage (Fletcher, 2002).
References
Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.
Buss, D. M. (1995). Evolutionary psychology: A new paradigm for psychological science. Psychological Inquiry, 6, 1-30.
Campbell, N. A., Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2008). Biology (8th ed.). San Francisco: Pearson.
Dawkins, R. (1996). Climbing mount improbable. London: Penguin.
Dawkins, R. (2006). The god delusion. London: Bantam Press.
Evans, D., & Zarate, O. (1999). Introducing evolutionary psychology. Cambridge, UK: Icon Books.
Fletcher, G. J. O. (2002). The new science of intimate relationships. Oxford: Blackwell.
Wednesday, September 22, 2010
Wednesday, August 25, 2010
Nature and Nurture
In my last post I gave a brief description of one of the key mechanisms that Charles Darwin proposed drove the evolutionary process – natural selection. To recap briefly, natural selection is the preservation of phenotypes that are advantageous to individual organisms in what Darwin termed the “struggle for existence” amongst organisms. I noted that phenotypes can be any of an organism’s observable characteristics – some feature of its anatomy, physiology or behaviour. Selection for behaviours is the realm of evolutionary psychology. Generally speaking, evolutionary psychology refers to any attempt to apply evolutionary theory to the study of psychology. However, over the last 20 years or so, the term evolutionary psychology has become synonymous with a particular set of theoretical assumptions put forward by a group of researchers, the most prominent of who include the anthropologist John Tooby and the psychologists Leda Cosmides and David Buss (Buller, 2005). I’ll go into a bit more detail about these theoretical assumptions a little later.
I also noted in my description of natural selection that there must be genes at least partially responsible for each of the variant phenotypes, which parents transmit to their offspring during reproduction. It has been demonstrated quite conclusively in countless studies that genes, as well as experience, make a contribution to our behaviour and our cognition, or mental processing. This makes perfect sense because genes help determine the structure and function of the brain. One simply needs to open any introductory level psychology textbook to see that this is the case. For example, children of one or both parents with schizophrenia, a devastating psychiatric disorder that may involve disturbances in thinking (delusions), perception (hallucinations), emotions and behaviour, are at greater risk of developing the disorder themselves than children of non-affected parents. This is true even in cases where the children have been adopted at birth and raised by non-affected adoptive parents, so genes probably play some role in the increased risk for developing the disorder (Nairne, 2006).
Notice that I stressed the point that experience, or environmental factors also make a contribution. I do not want the idea that genes make a contribution to our behaviour and cognition to be confused with genetic determinism, the idea that these traits are determined entirely by genetics. The environment will always play some role!
In my last post I suggested that humans have a strong tendency to develop a fear of snakes. This does not mean, of course, that all humans have a fear of snakes. When discussing the causes of specific phobias (irrational fear of a specific object or situation), Barlow & Durand (2002) note that several things have to occur for a person to develop a phobia. While there is evidence that our brains seem to be “pre-wired” by our genes to associate fear with certain objects and situations, such as snakes and spiders (that is, we seem to be able to make the association more easily than say with live electrical wires, which are also potentially dangerous - see Footnote below), some kind of traumatic conditioning (or learning) experience is still generally necessary. This experience need not be a direct traumatic encounter with a snake or spider, but could also involve observing someone else experiencing severe fear in response to a snake or spider, or even, in some circumstances, being told about a potential threat. If the "purpose" of fear is to increase the chances of survival by avoiding certain objects or situations it makes sense that this emotion can develop without needing to face any danger directly. For example, a child who has a mother who becomes extremely anxious whenever she sees a spider may themselves develop an anxiety around spiders. Barlow & Durand (2002) mention a case of a woman with a severe snake phobia who had never encountered a snake in her life but had been warned repeatedly when growing up about the danger of snakes in high grass. She was encouraged to wear high rubber boots to guard against the threat – and did so even when walking down the street.
Another "risk factor" for the development of a phobia is the tendency to get anxious about future contact with the feared object or future occurrence of the feared situation (Barlow & Durand, 2002). Such a tendency would more than likely be the result of genetic and early environmental influences combining to produce an anxious, or neurotic, character. While not all fear may be considered irrational or interfere with an individual’s ability to live a normal life, and therefore be considered a phobia, Barlow and Durand's (2002) model gives us a sense of how experience and genetics/biology can both contribute to the development of behaviour and cognition.
Footnote: This is an interesting point and will be touched upon again when I discuss the theoretical assumptions that dominate the field of evolutionary psychology.
References
Barlow, D. H., & Durand, V. M. (2002). Abnormal psychology: An integrative approach (3rd ed.). Belmont, CA: Wadsworth.
Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.
Nairne, J. S. (2006). Psychology: The adaptive mind (4th ed.). Belmont, CA: Thomson Wadsworth.
I also noted in my description of natural selection that there must be genes at least partially responsible for each of the variant phenotypes, which parents transmit to their offspring during reproduction. It has been demonstrated quite conclusively in countless studies that genes, as well as experience, make a contribution to our behaviour and our cognition, or mental processing. This makes perfect sense because genes help determine the structure and function of the brain. One simply needs to open any introductory level psychology textbook to see that this is the case. For example, children of one or both parents with schizophrenia, a devastating psychiatric disorder that may involve disturbances in thinking (delusions), perception (hallucinations), emotions and behaviour, are at greater risk of developing the disorder themselves than children of non-affected parents. This is true even in cases where the children have been adopted at birth and raised by non-affected adoptive parents, so genes probably play some role in the increased risk for developing the disorder (Nairne, 2006).
Notice that I stressed the point that experience, or environmental factors also make a contribution. I do not want the idea that genes make a contribution to our behaviour and cognition to be confused with genetic determinism, the idea that these traits are determined entirely by genetics. The environment will always play some role!
In my last post I suggested that humans have a strong tendency to develop a fear of snakes. This does not mean, of course, that all humans have a fear of snakes. When discussing the causes of specific phobias (irrational fear of a specific object or situation), Barlow & Durand (2002) note that several things have to occur for a person to develop a phobia. While there is evidence that our brains seem to be “pre-wired” by our genes to associate fear with certain objects and situations, such as snakes and spiders (that is, we seem to be able to make the association more easily than say with live electrical wires, which are also potentially dangerous - see Footnote below), some kind of traumatic conditioning (or learning) experience is still generally necessary. This experience need not be a direct traumatic encounter with a snake or spider, but could also involve observing someone else experiencing severe fear in response to a snake or spider, or even, in some circumstances, being told about a potential threat. If the "purpose" of fear is to increase the chances of survival by avoiding certain objects or situations it makes sense that this emotion can develop without needing to face any danger directly. For example, a child who has a mother who becomes extremely anxious whenever she sees a spider may themselves develop an anxiety around spiders. Barlow & Durand (2002) mention a case of a woman with a severe snake phobia who had never encountered a snake in her life but had been warned repeatedly when growing up about the danger of snakes in high grass. She was encouraged to wear high rubber boots to guard against the threat – and did so even when walking down the street.
Another "risk factor" for the development of a phobia is the tendency to get anxious about future contact with the feared object or future occurrence of the feared situation (Barlow & Durand, 2002). Such a tendency would more than likely be the result of genetic and early environmental influences combining to produce an anxious, or neurotic, character. While not all fear may be considered irrational or interfere with an individual’s ability to live a normal life, and therefore be considered a phobia, Barlow and Durand's (2002) model gives us a sense of how experience and genetics/biology can both contribute to the development of behaviour and cognition.
Footnote: This is an interesting point and will be touched upon again when I discuss the theoretical assumptions that dominate the field of evolutionary psychology.
References
Barlow, D. H., & Durand, V. M. (2002). Abnormal psychology: An integrative approach (3rd ed.). Belmont, CA: Wadsworth.
Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.
Nairne, J. S. (2006). Psychology: The adaptive mind (4th ed.). Belmont, CA: Thomson Wadsworth.
Friday, August 6, 2010
An Evolutionary View of Emotions
Geez, isn’t it crazy how time gets away from us sometimes? Eight months after my first post, here’s my second! They will get much more frequent, I promise!
Recently I was watching an episode of the British science fiction television series Doctor Who, in which Earth is invaded by a race of cybernetic aliens called Cybermen. According to the leader of these alien invaders the Cybermen were once human but during the cybernetic process “weaknesses” such as emotions had been removed from their brains. This description of emotions as weaknesses by the Cyberleader echoes a belief that is pervasive throughout popular culture, namely that emotions are the products of primitive parts of our brain that interfere with the ability of “higher” parts of the brain to think rationally. Good problem solving requires rational thought – the application of reason, logic, and deduction to arrive at a solution. Emotions only get in the way. But this belief is not just evident in popular culture. Researchers in psychology – the scientific study of behaviour and mental processes - have also tended to contrast “emotionality” with “rationality” (Buss, 2000). An alternative view of emotions that challenges this traditional view is that they are adaptations, traits that have been preserved by natural selection through our species’ evolutionary history because, far from interfering with problem solving, they have provided solutions to adaptive problems that our ancestors have faced.
There are a number of good introductions to Darwinian evolutionary theory. A good introductory web-site on evolutionary theory can be found at: http://evolution.berkeley.edu/ But briefly, according to Darwinian evolutionary theory, natural selection is one of the driving processes of evolution. Natural selection is a very simple mechanism that occurs when three prerequisite conditions are met in a population (Buller, 2005). The first condition is preexisting phenotypic variation. Phenotypes can be any one of an organism’s observable characteristics – some feature of its anatomy, physiology or behaviour. The second condition is that the phenotypic variation must be able to be fairly reliably passed onto the organism’s offspring. In Charles Darwin’s day people were aware that children tend to resemble their parents in certain characteristics, but the actual mechanism by which these characteristics were passed from parent to offspring was unknown. Nowadays we say that there must be genes at least partially responsible for each of the variant phenotypes, which parents transmit to their offspring during reproduction. Finally, the phenotypic variation must be responsible for differences in organisms’ fitness. Fitness is a measure of an organism’s ability to survive and reproduce.
Logically, the number of individuals of any given species cannot keep increasing indefinitely. Eventually, there are going be more individuals than can be supported by the environment due to a limit on available resources such as food. This means that living organisms are typically involved in a “struggle for existence” with other members of their population, competing for limited resources. In addition to trying to gain enough food to survive there is also the problem of not becoming food for something else! Some individuals will differ in slight ways that will give them an advantage in this “struggle for existence” and will give them a better chance of producing offspring than other individuals. A key factor in successfully producing offspring is, of course, surviving long enough to mate. The beneficial variations are more likely to be passed on to future generations. Gradually, these variations will spread throughout the entire population, as those individuals that possess them continue to out-compete the individuals that do not possess them.
An organism’s fitness is largely dependent on how well adapted its characteristics are to the demands or pressures of the environment it inhabits. These “selection pressures” can be thought of as adaptive problems, and some phenotypic variations provide better solutions to these problems than others, thereby improving the chances of survival and reproduction of those organisms that exhibit them. To give an illustrative example, a number of researchers that apply an evolutionary framework to studying human psychology argue that for the majority of our species’ evolutionary history poisonous snakes were a major threat to our ancestors’ survival (e.g. Buss, 2000). Because an encounter with a poisonous snake could prove extremely costly in evolutionary terms (death would have obviously eliminated the possibility of any future reproduction), there must have been a strong “selection pressure” to avoid them. The argument goes that the evolved “solution” to this adaptive problem of avoiding poisonous snakes has been a strong tendency for humans to develop a fear of snakes (Buss, 2000). Fear of snakes is certainly one of the most common fears that humans exhibit (e.g. Agras, Sylvester & Oliveau, 1969, as cited by Barlow & Durand, 2002, and Nairne, 2006). This is just one relatively straightforward example of the emotions-as-adaptations view that I mentioned earlier, just to give a sense of what I was getting at. In a future post I intend to take a much more critical look at a common evolutionary view of another emotion: jealousy.
References
Barlow, D. H., & Durand, V. M. (2002). Abnormal psychology: An integrative approach (3rd ed.). Belmont, CA: Wadsworth.
Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.
Buss, D. M. (2000). The dangerous passion: Why jealousy is as necessary as love or sex. London: Bloomsbury.
Nairne, J. S. (2006). Psychology: The adaptive mind (4th ed.). Belmont, CA: Thomson Wadsworth.
Recently I was watching an episode of the British science fiction television series Doctor Who, in which Earth is invaded by a race of cybernetic aliens called Cybermen. According to the leader of these alien invaders the Cybermen were once human but during the cybernetic process “weaknesses” such as emotions had been removed from their brains. This description of emotions as weaknesses by the Cyberleader echoes a belief that is pervasive throughout popular culture, namely that emotions are the products of primitive parts of our brain that interfere with the ability of “higher” parts of the brain to think rationally. Good problem solving requires rational thought – the application of reason, logic, and deduction to arrive at a solution. Emotions only get in the way. But this belief is not just evident in popular culture. Researchers in psychology – the scientific study of behaviour and mental processes - have also tended to contrast “emotionality” with “rationality” (Buss, 2000). An alternative view of emotions that challenges this traditional view is that they are adaptations, traits that have been preserved by natural selection through our species’ evolutionary history because, far from interfering with problem solving, they have provided solutions to adaptive problems that our ancestors have faced.
There are a number of good introductions to Darwinian evolutionary theory. A good introductory web-site on evolutionary theory can be found at: http://evolution.berkeley.edu/ But briefly, according to Darwinian evolutionary theory, natural selection is one of the driving processes of evolution. Natural selection is a very simple mechanism that occurs when three prerequisite conditions are met in a population (Buller, 2005). The first condition is preexisting phenotypic variation. Phenotypes can be any one of an organism’s observable characteristics – some feature of its anatomy, physiology or behaviour. The second condition is that the phenotypic variation must be able to be fairly reliably passed onto the organism’s offspring. In Charles Darwin’s day people were aware that children tend to resemble their parents in certain characteristics, but the actual mechanism by which these characteristics were passed from parent to offspring was unknown. Nowadays we say that there must be genes at least partially responsible for each of the variant phenotypes, which parents transmit to their offspring during reproduction. Finally, the phenotypic variation must be responsible for differences in organisms’ fitness. Fitness is a measure of an organism’s ability to survive and reproduce.
Logically, the number of individuals of any given species cannot keep increasing indefinitely. Eventually, there are going be more individuals than can be supported by the environment due to a limit on available resources such as food. This means that living organisms are typically involved in a “struggle for existence” with other members of their population, competing for limited resources. In addition to trying to gain enough food to survive there is also the problem of not becoming food for something else! Some individuals will differ in slight ways that will give them an advantage in this “struggle for existence” and will give them a better chance of producing offspring than other individuals. A key factor in successfully producing offspring is, of course, surviving long enough to mate. The beneficial variations are more likely to be passed on to future generations. Gradually, these variations will spread throughout the entire population, as those individuals that possess them continue to out-compete the individuals that do not possess them.
An organism’s fitness is largely dependent on how well adapted its characteristics are to the demands or pressures of the environment it inhabits. These “selection pressures” can be thought of as adaptive problems, and some phenotypic variations provide better solutions to these problems than others, thereby improving the chances of survival and reproduction of those organisms that exhibit them. To give an illustrative example, a number of researchers that apply an evolutionary framework to studying human psychology argue that for the majority of our species’ evolutionary history poisonous snakes were a major threat to our ancestors’ survival (e.g. Buss, 2000). Because an encounter with a poisonous snake could prove extremely costly in evolutionary terms (death would have obviously eliminated the possibility of any future reproduction), there must have been a strong “selection pressure” to avoid them. The argument goes that the evolved “solution” to this adaptive problem of avoiding poisonous snakes has been a strong tendency for humans to develop a fear of snakes (Buss, 2000). Fear of snakes is certainly one of the most common fears that humans exhibit (e.g. Agras, Sylvester & Oliveau, 1969, as cited by Barlow & Durand, 2002, and Nairne, 2006). This is just one relatively straightforward example of the emotions-as-adaptations view that I mentioned earlier, just to give a sense of what I was getting at. In a future post I intend to take a much more critical look at a common evolutionary view of another emotion: jealousy.
References
Barlow, D. H., & Durand, V. M. (2002). Abnormal psychology: An integrative approach (3rd ed.). Belmont, CA: Wadsworth.
Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.
Buss, D. M. (2000). The dangerous passion: Why jealousy is as necessary as love or sex. London: Bloomsbury.
Nairne, J. S. (2006). Psychology: The adaptive mind (4th ed.). Belmont, CA: Thomson Wadsworth.
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