Taking ADvantage
The Biological Basis of Human Behavior


Richard F. Taflinger

This page has been accessed since 28 May 1996.

For further readings, I suggest going to the Media and Communications Studies website.

This chapter examines human biological evolution over the last several millions years, and how that evolution has influenced how human respond to stimuli today.

Basic Biological Influences on Human Behavior:

Chapter Three

Biological Evolution

Human beings are animals.

This is not a reference to our behavior (although, of course, some people do act like animals). It is a reference to the fact that humans are biological creatures, as much as crocodiles, cougars, and capybara. We are the product of millions of years of evolution, our physical make-up changing to make us fitter to survive and reproduce.

However, although humans are animals, we also have something that no other animal has: the most complex social structure on Earth. We gather in families, tribes, clans, nations. We have an incredibly sophisticated method of interacting -- speech. We can communicate over time and distance through printing and broadcasting. Our memories are the longest, our interactions the most intricate, our perception of the world simultaneously the broadest and most detailed.

The combination of biology and society is what makes us what we are and do what we do. Biology guides our responses to stimuli, based on thousands of generations of ancestors surviving because of their responses. Our social structures dictate restrictions on and alterations in how we carry out our biological responses.

Neither biology nor society stands without the other. For some people, this is a contradiction -- either nature (biology) controls people, or nurture (society) does. But in fact we filter everything through both to determine how we react to stimuli. The following is a discussion of the two sides of human nature: first, the biological basis of our responses to the world around us, and second, the social factors that affect those responses and make us human.


The three main elements biology contributes to human behavior are: 1) self-preservation; 2) the reason for self-preservation, reproduction; and 3) a method to enhance self-preservation and reproduction, greed. I will discuss each in turn.


Self-preservation is keeping yourself alive, either physically or psychologically. The latter includes mentally or economically healthy. (Since human beings are very social creatures, we may also apply self-preservation to other people, such as our families. However, I will discuss that in the next chapter.)


A lioness slowly, stealthily, works through the tall grass toward the herd of wildebeest. A doe, unaware of the danger lurking in the grass, separates slightly from the herd. With a rush, the lioness bursts into a run to take down the doe. The startled doe bounds away, running and swerving, trying to escape. The lioness, unable to keep up the pace, gives up, and the doe escapes back into the herd.

A zebra is not so lucky, and the pride feasts.

The Donner Party was a group of settlers trekking to California in 1846. Trapped by snow in the Sierra Nevada Mountains, they survived as best they could. This included resorting to cannibalism when they ran out of food, eating the bodies of those who had died.


To be successful as a species, the members of that species must have a desire to survive long enough to pass on their genes to offspring. A species with a death-wish dies out rather quickly. Those species that don't die out have members that have devoted some attention to staying alive long enough to have young. It is from those individuals and therefore species that all living things are descended.

The desire to stay alive is an instinctive one, built into the psyche of the organism. The organism will seek those elements of its environment that will enhance its chances for survival. These include food, water, oxygen, and periods of rest to allow the body to repair any wear and tear on the tissues.

Alternately, it will avoid or evade those elements that might reduce its chances for survival. Such dangers include predators, starvation, dehydration, asphyxiation, and situations that can cause damage to the body.

These seek or avoid drives influence the behavior of organisms: iron seeking bacteria will move toward magnetism, gnus will migrate hundreds of miles to find new pastures, a human will resort to cannibalism; an amoeba will flow away from an electric current, an antelope will run from a lion, a human will obey a killer or withstand torture.

The desire to stay alive is also a selfish instinct, since it is personal survival that the organism is seeking. The reason for that is explained under REPRODUCTION.

Survival Through Evolution

A phrase that has often been misquoted, "Survival of the Fittest," actually means survival of the fit. By fit, I mean an organism has those attributes that allow it to get the most out of its environment: gather food, drink, oxygen, rest, sex. The better it is at doing this, the more fit it is.

At this point I should discuss the niche. A niche is a position within an environment that calls for certain attributes to exploit that environment. An environment can contain any of a variety of elements: amount of water, from ocean to desert; type of land, from marsh mud to solid rock; amount of vegetation, from none (the Arctic and Antarctic) to abundant (rainforests). It can also contain animal life, from the tiniest insects to blue whales and everything in between. It is the combination and degree of each of these elements that create niches.

As an example, let's look at just one of these elements. Say there are many small animals, like mice, in an area. A small carnivore like a wildcat could find a lot of food. Thus, it would fit into this niche and thrive. However, when the number of mice decreases, the wildcat can find less food, and has a lesser chance of survival.

If the wildcat has competition from other small carnivores, like foxes, the one that is particularly good as a predator, through cunning or speed or some other attribute, will catch more food. This lessens the amount of food available for the competition, and thus drives the competition out. If the fox is better at catching mice (that is, more fit) than the wildcat, the wildcat will either die or have to move to another niche in which it will be the better predator.

On the other hand, if there are no small animals but many big animals, like antelope, neither a fox nor a wildcat would have much success preying on them. Thus, they wouldn't fit in such a niche. However, large carnivores such as lions would.

Of course, nothing stays the same forever. Niches alter through geologic, climatic and, in the present day, man-made changes in land, water and air. A volcano can create a new island. An ice age can lock up huge quantities of water in ice caps and glaciers, creating areas of land where oceans once rolled. Continental drift can push seabeds to the tops of mountains. Humans can chop down forests and build cities. All these changes alter the niches, the environmental conditions under which the life in those niches live.

Of course, this means the life has to change as well, to match the new conditions. If it doesn't, it dies. An example is a moth in England. It was originally a mottled white, which allowed it to blend into the light bark of the trees in its area. However, in the 19th century factories in this area began to belch out soot from their chimneys that settled on the trees, changing the tree bark from mottled white to mottled black. The moth could no longer blend in and thus was easy prey to birds. However, some of the moths were darker and thus less noticeable. After a few generations of these darker moths surviving and passing on their genes, the standard color changed to mottled black, and the moth, now blending into the dark bark, survives.

Note that such changes are not conscious decisions made by the organism: the moth did not say to itself, "The bark is getting dark--I'd better change color, too." It is simply that there are variations between individuals in any species (an advantage of sexual reproduction and its combining of genes). Some of those variations are detrimental: the dark moth variations were easy prey when the tree bark was light. However, as the conditions in a niche change, those same variations can become advantageous, enhancing rather than weakening chances for survival.

Such changes in an organism's physical characteristics are, of course, accidental. If no variations exist in a species that contribute to survival when conditions change, or if conditions change too quickly for advantageous variations to be passed on to enough descendants,(1) the species can die out.

Survival Through Strategy

Other changes in an organism can develop over time. These are survival strategies, rather than physical changes, that improve the organism's chances for survival. For example, some animals have perfected the technique of hibernating during periods when the food supply is low. Marmots have developed a social structure that provides lookouts who watch for predators and sound a warning when one appears. Prairie dogs dig their burrows with multiple entrances and exits so if a predator comes in one door, the dogs can leave through another.

These survival strategies are adaptations to niche conditions, but unlike physical changes are not necessarily genetic changes. Such strategies as hibernation, of course, require genes that alter the animal's physiology to slow heartbeat, lower body temperature, and otherwise decrease its metabolism. Others are instinctive, hardwired genetically into the animal's brain, such as a fawn's curling up and freezing when predators are about.

However, some survival strategies are learned behaviors. That is, the young learn them from older animals that learned them from their ancestors. For example, most predators teach their young the techniques of successful hunting. In general, it appears the higher the complexity of the nervous system of the animal, the more likely strategies are learned rather than instinctive. Sharks, with a relatively simple nervous system, hunt by instinct and need no instruction on how to go about it. Lions, with a complex system, must learn the techniques of stealth, stalk, and attack.

Again, in most animals, the strategies are not conscious decisions, but responses to stimuli such as hunger, thirst, asphyxiation, fear, or exhaustion. If conditions change so the instinctive strategy is dangerous rather than beneficial, the animal can die. For example, the fawn's freeze response to fear would be deadly if there was no cover to hide in while frozen. The musk ox strategy is to form a stationary circle with the young in the center and the older members facing outward, rather than running away. This is excellent against wolves, but deadly when faced with spears and guns (perfect, however, for the human survival strategy of group hunting with weapons). The musk ox cannot consciously decide that this strategy isn't working and that they must try another.


The combination of genetic and learned responses to stimuli creates an animal's reaction to stimuli. For example, the genetically dictated instinctive reaction to a threat to self-preservation is the "fight or flight" syndrome. When threatened, an animal undergoes several physiological changes that have become genetically hardwired into the animal's body. The changes include an increased rate of respiration to provide more oxygen to the muscles, an accelerated heart beat to speed up the blood flow, a lessening in sensitivity to pain, and changes in the blood stream, including an injection of adrenalin and diversion away from the organs to the muscles. These physiological changes prepare the animal to either fight for survival or run away from danger.

However, learned responses can mitigate the instinctive, depending on the complexity of the animal's nervous system. That complexity increases an animal's options in reacting to stimuli. For example, an amoeba will avoid an electric field automatically -- an instinctive reaction unmitigated by a survival strategy. A starving rat, however, will run across an electrified grid that gives it painful shocks if there is food on the other side. It can learn a survival strategy -- the shocks, though causing the instinctive fight-or-flight physiological changes, aren't going to kill it. Starvation will.


All the above applies to humans as much as any other animal: humans desire personal survival; seek food, drink, rest, sex; fit into niches; must adapt to changing conditions.

Humans are subject to the same stimuli and reactions as any other animal. Hunger, thirst, asphyxiation, fear, and exhaustion are physical sensations that cause instinctive physical reactions. Most of these reactions are unpleasant, and people avoid the stimuli that cause them, or, if they're unavoidable, take actions to reduce them. Thus you eat when hungry, drink when thirsty, fight for air, run from dangerous situations, sleep. In any case, the reactions are good in that they tell you you're in a situation that could result in injury or death. These responses are instinctive, and we have no more control over them than we do over our eye color.

Actually, we do have control over our eye color. The reason we do is why our approach to self-preservation is different from all other creatures. We have a brain that is capable of perceiving and solving problems. We change our eye color with contact lenses. We react to a threatening situation through applying our brains to the problem and finding a solution to it.

The difference between humans and other animals is that, unlike any other animal (as far as we know), we can and do consciously respond or alter our response to a stimulus. The greatest example lies in the existence of amusement parks, where people deliberately subject themselves to stimuli that any other creature on earth would go to great lengths to avoid. Imagine, if you can, the reaction of a dog to a roller coaster. If it didn't leap out at the first movement, it would cringe in bottom of the car until it probably had a heart attack. Yet, humans go on such rides for fun, our minds accepting that the ride is safe, and thus control the terror such a thing would cause in any other creature.

Indeed, the physical manifestations of the stress of the workplace, such as ulcers, headaches, nervous breakdowns, is often considered a result of the fight or flight syndrome at work on the body, while the mind is required to remain under stimuli that no other creature would willing accept. For example, being bawled out by your boss would, in another animal, cause a fight or the chastised to run. Humans, though, stand, listen, nod their heads, say "yes, I understand" and go back to work (probably muttering uncomplimentary comments about the boss under their breath).

Even more, humans can alter rather than merely adapt to the environments in which we find ourselves to enhance our chances for survival. The invention of agriculture and the domestication of animals improved the food supply; the building of dwellings enhanced shelter from the elements; science and medicine have greatly increased human lifespan and the quality of that life. Human ingenuity has altered every aspect of the world to enhance the human life.(2)

However, humans live in an extremely complex society. Thus, self-preservation is a much more complicated proposition than among other animals. Eating to satisfy hunger is more than just finding proper vegetation or hunting; shelter for rest and recuperation is more than finding a convenient cave or nest; avoiding predators is difficult because it is often hard if not impossible to tell what is a predator (the only real predators on humans are other humans). Even avoiding dangerous situations (such as car crashes) is difficult because of human technology. Things can happen so quickly danger isn't apparent until it's too late to do anything about it.

To deal with the complexity, human society has become, to a large extent, an economic one. That is, the connections between unrelated people is often based on distribution of resources (related people connect more through personal attachment). I will discuss these social factors in human self-preservation in the next chapter.


"Greed is good."

Wall Street

The above quote is from the popular movie, WALL STREET, starring Michael Douglas. When it was spoken in the movie, it was used as an ironic counterpoint: the character who said it was very successful following the credo, but ultimately it was his downfall. The audience may have though it was poetic justice. The credo, however, is merely a statement of biological necessity.

Greed has an extremely negative connotation for most people. It conjures up images of Ebenezer Scrooge and Shylock, chortling over their gold and ignoring the plights and miseries of others. However, it is actually the gathering of resources, the more the better. Biologically, for any organism that is successful greed is good.

Any form of life must gather resources that allow it to survive and reproduce. The resources may be food, water, sunlight, minerals, vitamins, shelter. Without these things, the organism dies. Since the two most basic purposes of life are to live and to reproduce, it should do everything it can to avoid dying through a lack of resources.

Greed is one organism getting a larger piece of the pie, more of the necessary resources, than other organisms. For example, in the Amazonian rain forest, an occasional tree dies and falls. This leaves an opening to the sun in the continuous canopy of foliage. Plants and trees race each other to grow into that opening. The winners in the race fill the hole; the losers die through lack of sunlight. (Attenborough, 1990) The greed for sunlight means life.

Again, as for self-preservation and sex, greed is an instinctive reaction. When presented with resources, the instinct is to grab them, use them, take advantage of them. This isn't a conscious decision. An animal, when starving, wants more food; when thirsty, more water. If it means taking it from another animal, that's what it does if it can.

You may ask, what about those animals who feed their offspring, though they're starving themselves? Remember that the second purpose of life is to reproduce. This requires not only producing the young. Once it's born it must be kept alive until it's self-sufficient. If it dies, then all the time, effort and energy to produce it must be repeated to produce another one. However, once it reaches self-sufficiency the parent's genes will, most likely, be passed on to another generation. Keeping the offspring alive, even at the expense of the parent dying, is of paramount importance. Thus, a parent caring for its young at its own expense is not an act of selflessness; it's an act of genetic selfishness.

You may also point out that humans avoid being greedy. In fact, being greedy is something that is scorned, something to be ashamed of. Once again, as for self-preservation and reproduction, it's because humans are unique -- we have a conscious mind that influences their biological instincts. How that works is the topic of the next chapter.


1There is a theory of critical mass, that the gene pool for a species must be large enough (that is, the breeding population must be large enough) to provide enough variations to counter adverse conditions or events. For example, the African cheetah population appears to be descended from only a few individuals; apparently most of the species fell prey to a disease that only a few survived because of a genetic immunity. Those few represented a gene pool too small to provide much in the way of variation, and there is a fear that something, perhaps another disease to which the current population has no genetic immunity, will kill off the remaining cheetahs.

2 Of course, we can also argue that this same ingenuity has enhanced human life to the point that human life, and all other life on earth, is threatened. The human ability to alter the environment to help people survive has allowed so many people to survive that the Earth itself, which is need to support them, many not survive.

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