Altruism Part 1

Photo: Belding's Ground Squirrels, the subject of research on altruism


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