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Biological Altruism: Why Do Animals Help Each Other?
By Shana McAlexander
Product Developer
When a firefighter enters a burning building to save an elderly man, his willingness to risk his own life may be
attributed at least partly to his desire to help others. We see frequent examples of self-sacrifice by humans, in
both professional and spontaneous capacities. What about self-sacrifice among other animals? Evolutionary
biologists and animal behaviorists study such behaviors, looking for both immediate and evolutionary
explanations.
Rationales for self-sacrificing behavior are discussed and debated across the fields of animal behavior, evolution,
ecology, psychology, and philosophy. Most biologists agree on a concept of biological altruism: an act that
increases the recipient’s chances for reproductive success at the expense of the perpetrator’s.
Biological altruism presents an evolutionary puzzle. If individuals act under the pressures of self-preservation and
the desire to reproduce, then why would 1 organism help another, putting its own reproductive success at risk?
Further, if the tendency toward altruism is a heritable trait and individuals with the trait are less reproductively
successful, then why is the frequency of altruism relatively high?
Before getting into the changing views of altruism, I will present 3 often-cited examples from altruism research.
They may serve as case studies and topics of further research for your class.
Vampire bats
Vampire bats are long-lived, social animals that feed during the night and return to their group for daytime
roosting. Gerald Wilkinson’s research team at the University of California, San Diego investigated the altruistic
behavior in vampire bat groups in Costa Rica.
Researchers tagged each bat for identification. The bats can survive only 2 or 3 days without feeding. In the early
evening, the researchers captured a subset of bats and confined them, reintroducing them to their social group
later in the night after the others had returned from feeding. The feeders who donated food to their starving roostmates potentially compromised their own health.
The researchers tracked the relatedness between those donating and receiving the blood meals. There was a
greater frequency of blood sharing between related individuals within the group; however, unrelated bats also
exchanged meals. Over time, former recipients were observed feeding former donors, exemplifying “reciprocal
altruism,” a behavior associated with long-lived, close-knit animals.
Vervet monkeys
Like some other animals (e.g., prairie dogs), vervet monkeys give warning calls when they sense nearby
predators. Calling out a warning is considered an altruistic behavior because the signaler puts itself at greater risk
by giving away its own location to the predator.
Robert Seyfarth and Dorothy Cheney at the University of Pennsylvania investigated the system and types of
warning calls in a group of vervets. Juvenile callers sometimes overreact (e.g., a windblown leaf may stimulate
the “Eagle!” alert), but, as they mature, they learn to distinguish real threats and warn of them exclusively.
European minnows
Many fish species release a specific chemical after their skin has been damaged in some way, as by a predator.
This chemical was named Schreckstoff by its discoverer Karl von Frisch in 1938. Von Frisch found that European
minnows displayed a fright reaction when exposed to this chemical in the water. He inferred that the Schreckstoff
served as a warning to other minnows nearby.
For many people, this example is not as easy to view as altruism since there is no appearance of a “choice”
involved; however, the effect is that other individuals of the species survive longer as a result of the production
and release of the chemical.
Explaining biological altruism
Mid-twentieth century behaviorists such as Nobel Prize winner Konrad Lorenz believed that altruistic behavior
may harm the individual yet benefit the group as a whole, and that a group without altruistic members is less
reproductively successful.
The following chart models the reproductive success of a group of monkeys with arbitrarily assigned reproductive
success values and theoretical adjustments. Notice that Group 1 has a single altruistic member, while Group 2 is
all selfish. Even though the reproductive success of the altruistic Monkey A is low, the reproductive success for
Group 1 is greater than for Group 2 because of Monkey A’s sacrifice. The same model applies whether or not
members of the group are related (kin).
Group 1
Monkey
Gender
Altruistic
Basic
reproductive
success value
Adjustment for
altruistic group
Final
Reproductive
success value
A
Female
Yes
5
–2
3
B
Female
No
5
+1
6
C
Male
No
5
+1
6
D
Male
No
5
+1
6
20
+1
21
Total Group
Group 2
Monkey
Gender
Altruistic
Basic
reproductive
success value
Adjustment for
altruistic group
Final
Reproductive
success value
E
Female
No
5
0
5
F
Female
No
5
0
5
G
Male
No
5
0
5
H
Male
No
5
0
5
20
0
20
Total Group
In the mid-1960s, evolutionary biologists G.C. Williams and J.M. Smith rejected Lorenz’s assumptions on the
basis of the selective pressure that they assumed would work against any altruism trait. The main argument
against group-level altruism claims that any selfish (freeloading) individuals of the altruistic group will have a
greater probability of reproducing than the altruistic members. Thus, the “selfish gene” will prevail. The mode of
inheritance for the altruism trait is not well understood and is probably oversimplified by saying there is a single
selfish gene (or a single altruism gene); however, if the altruism trait is inherited, over many generations, the
frequency of altruism would be expected to decline within the group.
Current theories, first articulated by William Hamilton in 1964, tend to focus on kin selection. Hamilton predicted
that altruism occurs more often between genetically related individuals. If the members of a group are related, a
freeloader carries many of the same genes as the altruistic member. Because relatives share genetic makeup,
when an altruistic individual helps her relative, she is increasing the chance that their shared genes will be passed
on. If we apply this model to a related population containing some altruistic members, the gain in reproductive
success to the family group outweighs any loss in reproductive success of the altruistic individual. Consider a
situation where there is a diallelic, dominant selfish gene. The recessive, altruistic allele is also carried in some of
the selfish population. If the interrelated group survives more successfully as a result of the altruistic members’
behavior, then the recessive gene survives as well.
References>
Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex.
Magurran, A.E., Irving, P.W. and Henderson, P.A. 1996. Is there a fish alarm pheromone? A wild study and
critique. Proceedings of the Royal Society B (Biological Sciences) 263: 1551–5.
Okasha, S. 2009. Biological altruism. The Stanford Encyclopedia of Philosophy.
Seyfarth, R.M. and Cheney, D.L. 2000. Social self-awareness in monkeys. American Zoologist 40: 902–9.
Wilkinson, G.S. 1984. Reciprocal food sharing in the vampire bat. Nature 308: 181–4.
Name:___________________________________
Block:__________
Biological Altruism Questions
Directions: Answer the questions which follow based on the article
1.
What is one reason why an animal may be biologically primed to act altruistically?
What is the biological (think evolution) benefit of vampire bats of the same family (kin) acting
altruistically to one another?
2.
3.
Define “altruism”
4.
Analyze the chart… what conclusion can you draw from it?
5.
Do you think there is an “altruism gene?”
6.
Write a 1-2 page response explaining your answer to number 5.
You will be writing this as an 8-mark question. Therefore, be sure to define altruism,
explain why altruistic behavior may be biologically based, answer the question – is
altruism genetic – use the animal studies and research by Williams, Smith, and/or
Hamilton, to support your answer.