I stop by to see the folks at www.fightingaging.org every now and then. It’s always interesting to see what they are up to…
Here is a fairly typical entry drawn from the site’s archives.
My comments are in bold…
Biology is diversity; while the rule on predation and the evolution of longevity seems to hold for most species, there are always outliers: “mice are low on the food chain and rather likely to meet a bad end; consequently, there’s very little opportunity for genes that enhance longevity to benefit the animal (or even get expressed in the first place). Based on examples of this kind, biologists of aging generally predict that lower extrinsic mortality from predation is a positive influence on the evolution of longevity.
These sentences could benefit from being re-written. The meaning I take from them is:
a) The science of biology is varied and complex and offers many opportunities to stretch unrelated findings to buttress favorite pre-conceived notions.
b) Species which are subjected to intense pressure from predators tend to sacrifice traits associated with longevity in favor of traits that help them hide from, run from or defeat their predators.
c) This explains, for example, why their are no retirement homes for aged mice.
Hence, it is surprising that guppies exposed to predation actually appear to live longer (and age more slowly) than similar fish from a similar environment without predators. … This is an exception to two classical predictions of evolutionary theory: that low extrinsic mortality should be associated with longer life span, and that higher fertility should be associated with shorter life span.
When I read a statement like this, the first thoughts that pop into my mind are, “Where’s the evidence? What is the proof? How can I be sure that what the writer is claiming is actually true?” In particular, I would like to see a link to the article on guppie longevity. That would let me read the article and decide, for myself, whether I agree that: “guppies exposed to predation actually appear to live longer (and age more slowly) than similar fish from a similar environment without predators.” I did find the article in question and you can read it here. Without going into details it seems that what the authors of the article are actually claiming is that guppies exposed to predators develop a survival strategy that relies on relatively higher losses (to predators) of young guppies and greater survival among older guppies.
Some theorists have tried to accommodate this and other anomalous results within the standard framework, but we argue that the exceptions they carve out do not explain the results at hand. In fact, the findings suggest that population regulation has been selected at the group level, though this is a mechanism that most theorists regard with suspicion.”
Extra-ordinary claims require extra-ordinary proof. Changes in guppie populations are interesting but are not enough to overthrow one of the bedrock principles of modern biology:
Selection pressure is applied at the level of the individual, not the group.
For what it’s worth, this paragraph comes closer to capturing the real issues at hand.
Why do bats live longer than comparably sized and metabolically similar rodents? One idea is that chiropterans can escape predation more easily (because they can usually, though not always, fly away), thereby decreasing one major source of extrinsic mortality and exposing later life to selection pressure. In contrast, mice are low on the food chain and rather likely to meet a bad end; consequently, there’s very little opportunity for genes that enhance longevity to benefit the animal (or even get expressed in the first place). Based on examples of this kind, biologists of aging generally predict that lower extrinsic mortality from predation is a positive influence on the evolution of longevity.
The peculiar longevity of human is derived partly, but not completely from our position atop the world’s food chain….