December 07, 2004
Human Impulsiveness Selected For By Foraging Lifestyle?

David Stephens, a biologist at the University of Minnesota thinks some people hobbled by excessive impulsiveness because their ancestors benefitted from the behavior.

The new experiments were modeled on how animals encounter and exploit food clumps. The jays encountered one clump at a time and obtained some food from it. Then they had to decide whether to wait for a bit more from the same clump or leave and search for another clump. Not surprisingly, the birds still acted impulsively, preferring items they could get quickly. They considered only the size and wait time for their next reward--never a reward beyond that, even though it may have been bigger.

What did surprise Stephens was that the birds that went for the immediate reward were able to "earn" as much or more food in the long run as birds that were forced to wait for the larger reward or to follow a mixed strategy. The reason, he said, was that in the wild, animals aren't faced with an either-or choice of "small reward now or big reward later." What happens is that when they find a small bit of food, they don't wait; they just go back to foraging, and they may find lots of little rewards that add up to more than what they would get if they had to hang around waiting for bigger and better.

"Animals, I think, come with a hardwired rule that says, 'Don't look too far in the future,'" Stephens said. "Being impulsive works really well because after grabbing the food, they can forget it and go back to their original foraging behavior. That behavior can achieve high long-term gains even if it's impulsive."

The work may apply to humans, he said, because taking rewards without hesitation may have paid off for our foraging ancestors, as it does for blue jays and other foragers. Modern society forces us to make either-or decisions about delayed benefits such as education, investment and marriage; the impulsive rules that work well for foragers do more harm than good when applied in these situations.

"Impulsiveness is considered a big behavior problem for humans," said Stephens. "Some humans do better at binary decisions like 'a little now or a lot later' than others. When psychologists study kids who are good at waiting for a reward, they find those kids generallly do better in life. It looks as though this is a key to success in the modern world, so why is it so hard for us to accept delays? The answer may be because we evolved as foragers who encountered no penalties for taking resources impulsively.

We are no longer in the environments our ancestors evolved in. We have changed and continue to change our environments. Since natural selection takes many generations to adjust a species to environmental changes humans just are not adapted to the environments we are creating with technology. So Stephens' argument strikes me as very plausible.

Humans are going to have to adapt themselves and their offspring to modern environments. Successful adaptation will require the development of drugs, gene therapies, and stem cell therapies to adjust brains to be more adaptive and compatible with modern environments.

Share |      Randall Parker, 2004 December 07 02:05 AM  Brain Evolution

Anonymous said at December 7, 2004 11:07 AM:

I've long thought that Attention Deficit Disorder is badly misnamed, because its sufferers (including my son and, I suspect, myself) do not have a deficit of attention, they actually are hyper-attentive. This trait likely was of considerable survival value in prehistoric times. In a hostile environment, those who were easily distracted may well have been more likely to survive and pass on their genes than those who stayed focused and "on-task."

Garson Poole said at December 8, 2004 1:35 AM:

I suspect that many of our human forebears faced situations in which envisioning the future, carefully planning, and delaying gratification were essential to surviving and prospering. In some ways these behaviors are the opposite of "impulsiveness". Consider the following examples that are perhaps more relevant than bird behaviors:

A) Instead of sleeping in the open in a location that is vulnerable to predation a human might build a sturdy home. To do this effectively might require selecting a site, gathering material, planning construction, and building. Humans willing to invest time and energy based on contemplating the future and suppressing impulsiveness might be more likely to survive and propagate.

B) Instead of blundering directly toward a prey animal a human hunter might search for animal tracks, identify a location that animals regularly visit, quietly lie in wait for hours, and then kill or capture an animal. This strategy works best when a human can think ahead, lie still, avoid noisemaking, maintain attentiveness, and finally act quickly and dexterously.

C) Instead of gathering wild plants a human might engage in agriculture. This requires planting a crop, weeding the crop, nurturing the crop, and refraining from eating immature plants. Finally, after a period of months the crop might be ready for harvest and consumption.

Feel free to invent your own examples of delayed gratification, e.g, setting snares and traps that require long term monitoring, or creating and using nets for fishing. Perhaps, behaviors such as “impulsiveness” and “willingness to delay gratification” are too complex and mutable for the direct application of schematic evolutionary selection arguments. Perhaps too many interacting genes are involved. The ideas in evolutionary psychology are more convincing when they are applied to simpler behaviors.

jmgordon said at December 8, 2004 9:46 AM:

I doubt our survival was determined by being either all "impulsive," (i.e. seeking short-term rewards) or "deliberate," (i.e. seeking long-term rewards). Both activities require a certain amount of energy and therefore involve tradeoffs: generally investing in one robs some energy to invest in the other.

I hypothesize that any given environment in which people exist will have an optimum balance between impulsive and deliberate behavior - this balance being determined by how easily energy/resources are retrievable from the environment. In the environment of our ancestors - an environment of extreme scarcity - short-term behavior probably dominated: you and your kids have got to eat. Today, where our technology has given us HUGE reservoirs of the essentials, we can afford to invest in very long-term activities.

As a specific example, for the last several hundred years, many people longed to provide their children an education, but could not afford it. Too many short-term tasks needed tending: the children were needed to work the land, make the clothes, etc. Only when, over many generations, enough wealth was accumulated could the majority begin to forgo some of these short-term gains to idle their children in school.

The problem of course is we evolved in the environment of extreme scarcity, not the modern world. Therefore, our impulsive/deliberate ratio is probably not optimized for the modern world. Which, I think, was the point of the article.

Randall Parker said at December 8, 2004 12:03 PM:


I agree.

One refinement: Natural selection can produce ratios of genotypes and phenotypes that are stable in a given environment or that oscillate around some averages. So as a result of past selective pressures we might have some fraction of the population that is highly impulsive and along a continuum (since impulsivity is probably influenced by multiple loci) fractions of the population who are progressively less impulsive and finally a fraction of highly deliberate long-term oriented people. The latter people now have a big economic advantage in today's society.

Also, there may be different kinds of impulsivity influenced by different genetic variations that trigger different kinds of impulsiveness (sexual, violent, etc) in different situations.

Garson Poole said at December 8, 2004 3:47 PM:

Randall Parker says: “Also, there may be different kinds of impulsivity influenced by different genetic variations that trigger different kinds of impulsiveness (sexual, violent, etc) in different situations.”

Making distinctions between different kinds of behavioral impulsiveness is valuable. Indeed, behaviors can be sufficiently complex that they simultaneously exhibit “impulsive” and “deliberate” attributes (using the terminology of J. M. Gordon.) The paper under discussion examines the foraging behaviors of birds. Consider another prototypical bird behavior - migration. Instead of continuing to live and forage in a constrained locality a bird makes an arduous and dangerous journey to a destination that provides a superior habitat for a portion of the year. A naive external observer might think that a migrating bird is “acting with deliberation”, “seeking long-term rewards” and “delaying gratification.” The Pacific Golden-Plover provides a remarkable case of migration from Alaska to Hawaii. “This">">“This shorebird cannot swim. So, it flies non-stop for about 3,000 miles between the two distant places. This flight takes them about 2 days and they average about 60 miles per hour.”

Is this act “deliberate” or “impulsive”? I suspect that birds do not “think” about the long-term rewards of migration. Instead, the brain of a bird might be genetically programmed with a template for migratory behavior that is triggered and instantiated by environmental cues. This would be a great topic for an evolutionary psychologist. As genetic sequencing technology declines in cost it will be possible to sequence the brain-related genes of multiple birds. Yet, I would hesitate to extrapolate to human behavior from bird foraging or migration behaviors.

Bob Badour said at December 9, 2004 12:15 PM:


I took the study as providing an empirical model with quantitative results to explain the selective pressure for impulsivity among foragers. It shows that impulsivity can provide an advantage for foragers, but says nothing about farmers. Nor does the study say anything about migration. The selective advantages for deliberate farmers are unsurprising. One might reasonably expect to find greater impulsivity among populations who forage or who foraged in their recent history compared to populations who farmed.

That might suggest a genetic cause for why I am more impulsive than Randall, for instance. It doesn't suggest I have an avian genotype or say anything at all about my migratory predilections.

In short, I don't see why you brought up any of the issues you mentioned since they all seem rather irrelevant to the point of the study or its conclusions.

Garson Poole said at December 11, 2004 4:12 AM:

Bob Badour said, "I don't see why you brought up any of the issues you mentioned."
I apologize for my lack of clarity, and will try to explain why I brought up the issues you consider extraneous. First, consider what the researchers actually did. They studied one simplified artificial task that attempted to crudely model one aspect of bird foraging for one species of birds - Jays. Second, consider what the “Public Press Release” contained. It presented grandiloquent speculations about complex and intricate human behaviors like abusing drugs and marrying that are completely unrelated to the narrowly defined bird behaviors. A skeptical person would probably say the following: This bird behavior research tells us absolutely nothing about human behavior. The pop speculations about human “foraging” and “impulsiveness” in the “Press Release” are entertaining, but absurdly overreaching and not supported by the scientific work. Human “foraging” involves cognitively complex planning, anticipating, envisioning, and searching. Jays pecking at reward packets are irrelevant to this behavior. Human ‘impulsiveness’ is an ill-defined collection of multitudinous and divergent behaviors, each of which is too sophisticated for rudimentary bird brains. In short, the “marketing” of the research is over-the-top.

Lampoonery is hard to resist. Suppose a researcher performs a simple study on bird migration for one species. Next a “Press Release” is created that claims the research gives new insights into the human brain and explains why people have a deep impulse to fly to vacation spots in warmer climes. It also explains why North Americans are genetically programmed to buy second winter homes in Florida, and why ancient man crossed the Bering straits and headed south. Perhaps a bit of incredulity would be appropriate.

Why did I mention human behaviors such as shelter building, hunting, tracking, and farming in earlier comments? Because insights into human behaviors are often best obtained from the study of human behaviors. Evolutionary selection operated on humans that were expressing the behaviors mentioned.

Lastly, I hope my comments are not misconstrued. The bird research is valuable and interesting. Half-backed speculation can be fun and skepticism should not be heavy-handed. Also, it is possible that bird behavior research might somehow give insight into human behavior, but I could not find any evidence for that in the cited work.

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