Cultural Selection

In humans there are examples of alturistic behaviors that appear to be difficult to explain by kin selection of reciprocal altruism (e.g. soldiers sacrificing their lives in battle, police or firefighters risking their lives, catholic priests remaining celibate).

Genes are self replicating molecules. Genes produce our bodies which in turn produce more copies of their genes. Richard Dawkins has suggested that we think about genes as being "replicators" and our bodies as being "vehicles" whose job it is to make more copies of the replicators. If we can not explain altruistic behaviors as strategy for increasing the transmission of genes into the next generation them maybe we need to search for another kind of "replicator". Dawkins has suggested that "ideas" (he calls them "memes") are also capable of self replication. Because ideas differ in how long they survive and how well they are passed on it should be possible to have selection for ideas (cultural selection).

Expected Learning Outcomes

By the end of this course a fully engaged student should be able to

- identify examples of altruistic behavior that might be explained by cultural selection
- be able to compare and contrast "natural selection" with "cultural selection"

Further Readings

Cultural evolution http://plato.stanford.edu/entries/evolution-cultural/

As I mentioned in class, one of my favorite books of all time is "The Selfish Gene" by Richard Dawkings. He discusses some of his ideas about cultural selection in the final chapter of this book. Here is a link to that chapter in case you are interested
http://www.rubinghscience.org/memetics/dawkinsmemes.html

Reciprocal Altruism

Altruistic acts among non relatives can be understood by reciprocal altruism. As we discussed in class we would expect reciprocal altruism to be limited to species that show long term associations and are "smart" emough to be able to recognize individuals and remember who owes them and who does not.

Examples of Past Test Questions (answers at the bottom of this post)

1. It is not uncommon for college students to share items such as shampoo with their roommates. Which of the following hypothesis best explains this behavior?
(a) group selection
(b) kin selection
(c) reciprocal altruism
(d) selfish behavior
(e) altruistic behavior

2. Which of the following terms apply to a roommate who borrows your shampoo when she/he has run out, but will not allow you to borrow their shampoo when you need it?
(a) altruistic
(b) mutualist
(c) cheater
(d) a and c
(e) b and c



Further Readings

Reciprocal Altruism http://www.bbc.co.uk/nature/animals/mammals/explore/altruism.shtml

Reciprocal Altruism in Vampire Bats http://www.bio.davidson.edu/people/vecase/behavior/Spring2002/Perry/altruism.html

If you are interested in learning more about Evolutionary Psychology here is a link to a bunch of Frequently asked questions. Some of this goes into way more detail than we need to be worried about for this class.
FAQ Evolutionary Psychology http://www.anth.ucsb.edu/projects/human/evpsychfaq.html

Expected Learning Outcomes

By the end of this course a fully engaged student should be able to

- define reciprocal altruism
- discuss the conditions under which altruistic acts can be explained by reciprocal altruism
- examine an example of an altruistic behavior and determine whether reciprocal altruism is the best explanation
- explain how participants benefit by being involved in reciprodal altruism in real world examples (e.g, vampire bats)
- define a cheater in a reciprocal altruism system and discuss (a) why cheating is a problem in the system and (b) what organisms can do to reduce cheating
- discuss Trivers' ideas about how human psychology has been influenced by reciprocal altruism (be able to provide your opinion about Trivers' ideas and be able to back up your opinions)


Answers 1. c even though this is an example of altruistic behavior, the best explanation for this behavior is reciprocal altruism) 2. c

Altruism. Part 2

Question to Think About

Some birds have a behavior known as "helping at the nest". A female bird will sometimes help another bird rear offspring rather than laying her own eggs and raising them. There are two different hypothese to explain this behavior. First, this may be an example of an altruistic behavior that can be explained by kin selection. Alternatively, this may be an example of a purely selfish behavior. It is possible that young inexperienced birds are not very good at raising offspring the first time they try and by helping another bird to raise offspring they may get practice that makes them better at rearing offspring later on.

1) Explain how you as a scientist would conduct a study to distinguish between these two alternative hypothese.

2) Should a female bird who is capable of raising three offspring on her own help her sister to raise her sister's offspring if helping her sister allows her sister to raise five more offspring? Be sure that you would be able to explain to someone else how you determined your answer.

If you post your answers to the blog then I will be able to take a look at them and you can also get some feedback from fellow students.

Old Exam Questions

Here are some examples of old exam questions dealing with altruism. See if you can figure out the correct answers (answers provided at the bottom of this post).

Researchers studying black-tailed prairie dogs conducted an experiment where they dragged a stuffed badger (a predator of prairie dogs) across the colony. They repeated the experiment 698 times over the course of 3 years. The researchers observed that individuals with no offspring in the colony gave a warning call 19% of the time whereas individuals with offspring in the colony called almost 50% of the time. Which of the following could explain why individuals with no offspring would ever call?
(a) group selection
(b) other squirrels will return the favor in the future
(c) they have other relatives in the colony
(d) a and b
(e) a, b, or c would explain this observation


Which of the following are examples of an altruistic trait?
(a) an African wild dog sharing food with other members of the group
(b) a female choosing to mate with a symmetric male
(c) a sterile worker bee helping her sister (the queen) to reproduce
(d) a and c
(e) neither a, b, or c


Further Reading

Here are links to a couple of articles you might want ot take a look at-

Altruistic behaviors http://www.eoearth.org/article/Altruistic_behaviors

Kin selection http://www.eoearth.org/article/Kin_selection

More advanced reading

One of the problems with introductory courses is that we have to cover so many topics that it is not possible to go into very much detail over any of them. If you are interested in learning more about kin selection and altruism the following article would be good to look at.

Kin selection: fact and fiction. http://westgroup.biology.ed.ac.uk/pdf/Griffin&West_02.pdf

Answers to the test questions: 1) c 2) d

Why Group Selection Does Not Work

Photo: Large flock of European Starlings (a bird)




Group selection is the hypothesis that organisms have the traits they do (including altruistic traits) because selection has produced traits that assure that species survive. Although this is intuitively an OK idea, it turns out that it doesn't work.

Have you ever noticed large "roosts" of birds in trees around town. Roosting birds gather by the hundreds or thousands in one, or a few, trees (maybe you have mistakenly parked you car underneath a roost and suffered the consequences). Biologists are interested in understanding the causes of roosting behavior. People who support the group selection hypothesis have proposed that the reason that these birds are roosting is that it gives them an opportunity to examine how large their population is. Becasue the birds do not want to overpopulate their environment, because overpopulation could lead to a loss of all of the food so that the entire species dies, birds want to know how many other birds are there so they know how much to reproduce. If birds see that the roosts are large then they know that the population is large so they decide to produce only a few babies. However, if the birds see that the roost is small then they are decide to produce many babies. Thus, the population never gets so large that they eat up all of the food.

Unfortunately, the math required for group selection just doesn't work out. Imagine a species of birds that mated monogamously for life. If the parents wanted to keep population sizes constant than their best strategy would be to produce two offspring during their life so that they make just enough kids to replace themselves. For this to happen all females would have a gene that said "make two babies". Imagine that a mutation occurs that says "make three babies". This mutation would quickly spread througout the population so that eventually all females would produce babies.  If mutations that said produce 4 or more babies occurred then these mutations would also spread. It is thus possible to imagine that each female would make so many babies that the population would indeed get large enough to consume all of the food which would cause the population to go extinct.  Thus, the math of natural selection does not allow organisms to artificially reduce their fitness for the "good of the species".

The observation that led group selectionist to thinking that roosting and reproduction could be explained by group selection was that females produced fewer eggs when more individuals were at the roost than when fewer individuals were at the roost. Can you think of another hypothesis to explain this observation?

So why do birds form roosts? There are at least two hypotheses. First, some scientists propose that organisms roost because they are safer from predators when living in large groups. Others think that organisms form roosts because they can benefit from information gained by living with lots of other individuals. For example, if you flew to the south to look for food and didn't find much and you noticed that those birds returning to the roost from the north looked well fed, then you might head out to the north the next day.

Expected Learning Outcome

By the end of this course a fully engaged student should be able to

- discuss why the classic notion of group selection does not work in nature

Altruism- Part 1

Lecture Video to Watch


http://mediacast.ttu.edu/Mediasite/Play/63042145bb50446dbff54ad0f1d7c7611d?catalog=4dc7289a-d3e0-4ae5-8fdc-5b86c027a06b


From our discussion about natural selection you should have learned that organisms have the traits they do because traits that produce phenotypes that are more successful at transmitting genes to the next generation (surviving and reproducing) become more common in a population over time. Thus, we expect organisms to have traits that maximize their individual survival and reproduction (we call these selfish traits).



Examples of Altruistic Behaviors



1. Broken wing display by kildeer
kildeer live around here so you should be able to see this behavior later on this spring (that will require going outside!)

http://www.youtube.com/watch?v=TNG7y0caqj0



2. Group defense in musk oxen
you can't see this around here even if you go outside.

http://www.youtube.com/watch?v=pb6Rke7jiTc



3. Food sharing in African Wild Dogs

http://www.sandiegozoo.org/animalbytes/t-wild_dog.html



4. Prairie dogs giving warning calls

http://www.youtube.com/watch?v=rXCPaNWcTFo



We should originally be a little bit confused when we learn about altruistic traits. How can genes that produce traits that decrease an organisms abilty to survive or reproduce become more common in a population?!? Luckily, we have learned that understanding what happens in natural selection requires us to focus on the transmission of genes. Apparently, organisms that behave altruistically are actually passing on more genes by behaving altruistically than they would by behaving selfishly.  How can this be? (this problem perplexed Darwin).



Fortunately, a lot of really smart scientists have thought about altruism and have recognized that their are a variety of different ways that organisms behaving altruistically could pass on more genes than organisms acting selfishly. There are at least 4 different hypotheses that can explain the evolution of altruistic behaviors (one of these will probably only help to explain altruism in humans).

The first explanation for why organisms were altruistic was the idea of group selection. Group selection is the idea that organisms have traits becasue those traits "assure the survival of the species". At first glance this seems like a pretty useful idea, but it actually does not work and it has been a very difficult idea to remove from the minds of the general public even though scientists have know that it is wrong and unecessary (there are much better theories about the causes of altruism) for over forty years. It would take a while for me to explain why group selection doesn't work so I won't spend any more time talking about it either in class or here on the blog. However, if you are interested in learning more about this I would be happy to chat with you.



It is important for this class that you are able to understand under which conditions the other hypotheses could explain the presence of altruistic behaviors.



Hamilton's Rule



Hamilton's Rule is a mathematical equation that helps scientists understand under which conditions organisms should behave altruistically and when they should behave selfishly. It is important that you understand (1) how sceintists use mathematical models to help us understand the world and (2) what Hamilton's Rule tells us about when organisms should behave altruistically.



Suggested Readings

Biological Altruism- http://plato.stanford.edu/entries/altruism-biological/



Expected Learming Outcomes



By the end of the course a fully engaged students should be able to

1) define altruistic traits and provide several examples

2) compare and contrast selfish traits and altruistic traits

3) explain why altruistic traits at first glance appear to be difficult to understand based on what we know about the process of natural selection

4) discuss at least four possible hypotheses that explain the presence of altruistic traits and explain under which circumstances these theories are expected to apply

5) use “Hamilton’s Rule” as an example to illustrate how biologists use mathematical models to help them understand biology

6) discuss how Sherman’s work with Belding’s Ground Squirrels provided support for Hamilton’s Rule

7) be able to determine which hypothesis best helps you understand any examples of altruistic traits that I give you and be able to justify that answer