Chapter 3 Notes
There are several problems that we are faced with in order to survive. These were
labeled “hostile forces” by Darwin and include: climate, weather, food shortages, toxins,
diseases, parasites, predators, and hostile conspecifics (members of the same species).
These created adaptive problems which yielded survival solutions.
Since humans have always had to interact with the living environment, we have
learned to identify what is and is not safe for us to be around because we know the
“essence” of the organism. This intuition is called “folk biology” and can be found early
on in life and across different cultures. For example, dividing species into plants and
animals. This universal folk biology is believed to be a product of evolution because it:
(1) can be seen early on in life without being taught, (2) is universal across cultures, (3) is
a survival mechanism.
Food Acquisition and Selection:
Obtaining food was a very important and arduous task for our ancestors. It is an
activity that most animals dedicate most of their time to. The biggest problem with
finding food was to have enough of it with the nutrients that we need without eating
toxins that could hurt our bodies. Food selection affects omnivores (species that eat plants
and animals) in particular because plants have many toxins in them to protect themselves
from being eaten.
Food Selection in Rats
When they are infants, rats do not face these problems of food consumption
because they only feed off of their mother’s milk. One of the evolved mechanisms that
they have is to adjust their eating behavior when their bodies do not have enough water,
calories, and/or salt. Rats have “neophobia”- a strong aversion to new food. When they
eat a new food, they do it in very small doses so that they can see if it makes them sick.
This is another evolved mechanism which solves the adaptive problems of food selection
for rats.
Food Selection in Humans
The importance of food for humans can be seen in how much we spend on it.
Western countries spend 21 percent of their income on food, while less wealthy
countries, such as China, spend 50 percent of their income on food. Eating is a social
activity for humans. Various cultures show the importance of food for them in different
ways such as having words for different types of hunger and having special feasts, to
name a few. On a daily basis, our minds are usually focused on food.
Just like rats, we too have an evolved mechanism to ensure that we don’t ingest
natural toxins. Some of these mechanisms are: gagging, spitting, vomiting, and having an
aversion to the smell/taste of certain foods. The emotion of disgust is believed to assist us
because we are most repelled by things that are harmful to us, such as feces, poor
hygiene, etc. Therefore the disgust helps us to not come in contact with such substances.
Why Humans Like Spices: The Antimicrobial Hypothesis
Every time we eat we are facing a potential danger because we are putting
something potentially toxic into our bodies. Today it is not such a major problem, but it
was for our ancestors. They solved this problem by cooking their food. They also used
spices. The Antimicrobial Hypothesis says: “spices kill or inhibit the growth of
microorganisms and prevent the production of toxins in the foods we eat and so help
humans to solve a critical problem of survival: avoiding being made ill or poisoned by
the food we eat”. The evidence shows that spices do kill bacteria. More spices are used in
hotter climates where food can spoil easier. More spices are used in meat dishes than in
vegetable dishes because more bacteria resides in meat. Also, there have been more cases
of food poisoning in countries that traditionally use fewer spices in their dishes.
Why Humans Like to Drink Alcohol: An Evolutionary Hangover?
Humans have eaten a lot of fruit for millions of years. We prefer the ripest fruit,
which contains high levels of sugar and ethanol. The amount of ethanol in ripe fruit,
however, does not compare to the strength of an alcoholic beverage. The Frugivory Byproduct Hypothesis says that humans have a liking for drinking alcohol because of our
liking for ripe fruit, which contains small amounts of ethanol.
Sickness in Pregnant Women: The Embryo Protection Hypothesis
Pregnancy/morning sickness: a heightened sensitivity and nauseous reaction to
certain foods that women experience during the first 3 months of pregnancy. This is an
adaptation to keep pregnant women from ingesting “teratogens”- toxins that could harm
the baby. In particular, the foods that women do not like during this time are: coffee,
meat, alcohol, and vegetables. If they do consume these foods, they may vomit, which
keeps the food from reaching the fetus. Women experience this sickness during the time
when the vital organs are developing in the fetus, and therefore these toxins would be
particularly harmful. The foods that women dislike the most are the ones that contain the
most toxins. Women are more likely to have a spontaneous abortion/miscarriage if they
do not experience morning sickness during their first trimester. This has been found in
other cultures as well, but more cross-cultural research is needed in this area.
The Hunting Hypothesis
Food acquisition has been said to be an integral part of evolution because it is
linked to the emergence of modern humans. Humans eat more meat than any other
primates. It is very difficult for us to be vegetarians and still get all the nutrients we need.
Meat has been a critical part of our diets for thousands of years. Our bodies show that we
have been meat-eaters for many years. We have many small intestines which are made
for breaking down protein-rich food, like meat. Other evidence is found in the structure
of our teeth, the vitamins we can and cannot produce, and fossil remains.
The provisioning hypothesis says that male humans have a major parental
investment in their children. They hunt meat to bring back to their offspring because it is
high in calories and is therefore worth transferring the distance needed. Hunting can
explain strong reciprocal altruism and social exchange in humans. It would be very
difficult to hunt by oneself all the time; the man would not necessarily catch something
each time. Also, if he kept the meat all to himself, it would probably spoil. Therefore,
humans found it more beneficial to share. The sexual division of labor can also be traced
back to hunting. Males’ physical strength made them better suited for hunting than
women, who were left to stay home and care for the children. Hunting also explains the
surfacing of stone tools.
The Showoff Hypothesis says that women prefer men who show off their
valuables because they could benefit from them. They can offer these men special
treatment in return.
The Gathering Hypothesis
This hypothesis says that stone tools were invented and used not for hunting, but
for digging up and gathering various plants. After this came the invention of containers to
hold the food and more advanced tools. Helps account for the fact that our ancestors had
a lot plant food in their diets. Also shows that men were not solely responsible for
bringing home the food.
Comparing the Hunting and Gathering Hypotheses
The gathering hypothesis does not account for the division of labor between the
sexes observed across a wide variety of cultures, with men hunting and women gathering.
The hunting hypothesis can explain this behavior. The gathering hypothesis also does not
explain: high parental investment by human males, male coalition, humans in
environments that don’t have plants, the small intestine that processes meat, alliances in
humans.
The Scavenging Hypothesis
Scavenging- the retrieval of dead carcasses killed by other animals. Humans
might have been both scavengers and hunters, because it is unlikely that we were purely
one or the other. There are very few cases in nature of a pure predator (cheetah) and a
pure scavenger (vulture). However, this hypothesis leaves a lot of questions unanswered.
It is agreed that human ancestors were omnivores.
Adaptation to Gathering and Hunting: Sex Differences in Specific Spatial Abilities
Men should show superior abilities in the types of spatial tasks that would have
facilitated success in hunting, and women should be better at “spatial location memory,”
which is hypothesized to be an adaptation to gathering. Many studies have shown this to
be true.
Problems of Survival
Finding Shelter
The Savannah Hypothesis:
When faced with the problem of finding a place to live, our ancestors looked for
locations with abundant food and water and with cover from weather and predators. The
savannahs of Africa offer climate that meets these requirements.
People’s Preferences Today
Experiments using a subjects preferences for different photographs, have shown
that even today, people still prefer these natural, ideal environments that our ancestors
did. Why are ocean views so desirable?
Three Stages of Habitat Selection
Stage 1: Selection:
Is this habitat one we should stay in? Is it hidden enough that we will be safe
from predators, yet open enough to where we can keep watch around us?
Stage 2: Information Gathering
Assessment of risks and benefits; exploration of the terrain.
Stage 3: Exploitation
Should we stay long enough to use up the resources or will that make us
vulnerable to some sort of danger? There is usually a trade-off. For example, a location
with good foraging may leave you susceptible to predators.
Seasons and weather
Today we are pleased at the sight of green, ripe, budding plants. Example: Our
love of flowers; flowers indicate abundance in food for our ancestors.
Combating Predators and Other Environmental Dangers: Fears, Phobias, Anxieties, and
“Evolutionary Memories”
Fear is a survival tool that urges us to avoid danger and stay alive.
Tools for Staying Alive
Freezing: stop, assess situation, do not let predator know you are present
Fleeing: distances an organism from the threat
Fighting: fighting a predator may neutralize the threat by destroying it or causing
it to flee
Fright: person plays dead, predator may lose interest or let their guard down,
gives opportunity to flee
Fainting: helps warfare noncombatants (women and children) show enemies they
are not an immediate threat (unique to humans)
Submission and Appeasement: usually in response to members of one’s own
species, ex. the dominant male. May prevent a physical attack.
Most Common Human Fears
Human fears today are fears of the environment of yesterday. Ex: we aren’t
afraid of cars or electrical sockets, but are afraid of snakes and spiders.
Childrens Fears
Develop certain fears around 5 months, the age they start to crawl, the age they
might wander away from their mothers. Ex: fear of heights, recognition of spiders, fear of
stranger, separation anxiety (9-12 months), fear of animals (2 years)
Fear and Attention
Our built in fear mechanisms, affect what we attend to and how we perceive
things. Ex: a spider image embedded in a flower was picked up quicker than, neutral
images embedded in flower. We perceive sound coming towards us as louder than sound
leaving us.
Darwinian Medicine: Combating disease
Fever
Taking medicine to reduce a fever will prolong an illness. Fever is an
evolutionary, natural defense against pathogens.
Iron Poor Blood
The body naturally withholds and reduces iron in the blood, apparently to
starve bacteria.
Why do People Die?
The Theory of Senescence
Senescence: the deterioration of all bodily mechanisms as organisms grow older.
Selection only operates to keep an organism alive long enough to reach its reproductive
prime and raise offspring until they are independent
Plieotropy: a gene can have two or more different effects. Some genes can help in
early life two boost reproductive probability, but hurt later in life for survival. Example:
an abundance of testosterone in men early on can help reproduction, but later can
contribute to prostate cancer.
Males are designed to die sooner. Males must compete for females, their genes
are selected to competitively reproduce, they therefore have more plieotropic genes that
hurt survival later on.
The Puzzle of Suicide
Why would organisms kill themselves if selection wants to pass on DNA?
Wouldn’t this tendency be eliminated from selection?
Kin Theory: If organism feels like a burden to family, they may feel like they will
inhibit the transmission of genes to the next generation via their kin.
Sexual Disenfranchisement: People who feel they are not successful or attractive to the
opposite sex. Ex: during their mid twenties men are six times more likely to
commit suicide than women.
Edited by Liz Bohley and Sammy Morris