evolution - Empirical evidence for Group Selection?

A controversial concept in Biology "Group Selection", has caused confusion and conflict amongst scientists since the since the mid 1990s. The more general realm of study is termed the "unit of selection" discussion.

Definition

A simple working definition for "group selection" (edit/discuss this!) is:

"Selection for traits that would be beneficial to a population of units at the expense of an individual unit possessing the trait" (here)

Question

"What examples of group-selection are there?"

To add more structure, perhaps answers would consider the following details:

• Organism/Species in question


• Unit that experiences cost in fitness


• Group that experiences benefit in fitness


• Group-selected trait



• Explanation

Forward Example (trait whose presence benefits the group)

• Organism: Homo sapiens, Humans


• Unit: Cells and their genes


• Group: Collection of all cells in one individual Human body


• Group-selected trait: anti-cancer traits, e.g. apoptosis (programmed cell death) via p53 ("guardian angel" gene that "kills" cancerous cells)


• Explanation: Apoptosis is costly to the perspective of a cell, since it kills the cell and its genes. This enables the individual as a whole to live for long enough to mate and yeild offspring. Fitness of cells relative to other cells in the body is reduced, but fitness of the genome as a whole of that individual is increased relative to other individuals of that population -as a result of cancer-directed apoptosis.

Reverse Example (trait whose absence benefits the group)

• Organism: Cervus elaphus, Red Deer


• Unit: Individual red deer and their genomes


• Group: Isolated population of red deer and the population gene pool


• Group-selected trait: Lethal potential of antlers (e.g. sharp single antler instead of two blunt antlers).


• Explanation: Consider a one-antlered stag, whose single antler is imbued with a jagged edge and is the product of a point mutation in his genome. During a rut he is able to win against other males as his antler inflicts potentially fatal injuries. This allows him to mate many females and have many offspring - however this leaves the population at risk of becoming extinct since the mating season would either have too few males to form a rut, or due to deleterious inbreeding defects in the next generation.

Links

Of course do not feel restrained in your answers by the above suggestions - the point is to discuss the topic and learn!