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RE: FW: A Perspective on Cope's Rule
"Isn't part of the reason for needing huge litters because many fewer of the
offspring live to sexual maturity? Otherwise populations would be growing
exponentially, overwhelming available resources. If so many offspring die,
their rate of evolution won't keep pace with the rate of producing
The rate of evolution wouldn't be so wildly different from that of larger
Milbocker: Dying offspring is a function of evolution, or natural selection.
A population experiencing high rates of modification to its genetic code
would expect to have a high death rate. For high rates of evolution one
would want to eliminate the inferior body plans before sexual maturity,
otherwise there is no selection.
"By looking at just number of generations, it is probable that size may have
little causal effect on evolutionary rates. Albeit given that most smaller
organisms tend to have much shorter intervals between generations
larger species, smaller animals over time should evolve at much higher rates
than larger ones."
Milbocker: This statement seems to be self-contradictory. I agree with the
statement smaller animals should evolve at higher rates.
Stasis seems like a very strong word. It would only be a halt in size
increase, while the critter may continue to change in a hundred other ways
retaining the diversity that you say it would lack). Stasis ala Eldridge
happening here. Many VP'ers fight the reality of stasis anyway (I don't,
Milbocker: The word stasis was taken from my memory of the punctuated
evolution literature, it's meant to be taken relative to the rate of
evolution occuring after major extinction events. It would certainly be
incorrect to assert evolution actually stops. However, evolution optimizing
to a particular environmental circumstance can act to reduce diversity by
increasing specialization, and tweaks to a body plan that is fatally
specialized do not contribute to diversity needed for survival.
>Hence, when the
inevitable extinction event occurs, the large animals lack the genetic
diversity to cope (no pun intended).
"Well, that would explain why the sauropods were so unsuccessful, correct?
I do not accept that size is such a disadvantage. There are numerous
Milbocker: Success is not at issue, and the sauropod body plan underwent
more changes immediately after each extinction event than during the stable
It's not genetic diversity which is the problem...at least not directly.
Large organisms tend to require greater levels of resources than smaller
and thus possess much smaller populations (they are K selected species
afterall). When some sort of environmental perturbation occurs, these larger
may be able to cope easily and the population would decrease dramatically
become extinct). Even if the population is able to rebound, genetic
would be greater impared.
Milbocker: Not sure I follow your argument above. My assertion is that if
you had 100 foot sauropods and 1 foot sauropods, the poorly preserved 1 foot
sauropods would be more likely to carry the genetic resource for the
post-extinction next generation of sauropods.
I could have sworn that convergence is already extremely common?! Given
physical, developmental and phylogenetic contrainsts there are only so many
possible morphological trajectories. Also, ecological niches tend to require
sort of modications
Milbocker: I agree for periods between extinction events, but cladistics
assumes the opposite, that convergent evolution is relatively rare, that
species "radiate" they don't converge. The practice of taking a single
outgroup taxon to start a cladogram is symptomatic of this point of view.