Michael Lorrey responded:
>Maximum body size has not been increasing. It is a function of several
>things, mostly average environment temperature. Animals during the
>glacial periods were much larger than their current counterparts, ...
Curt Adams also responded:
>In land animals, body size hasn't been increasing for quite a while.
>... I did miss something. What exactly do you mean by a local tendency?
Eugene Leitl further responded:
>I think there is some evidence for "progress":
>- animal cerebralization quotient has risen
>- taxa longevity has risen, indicating risen adaptation to a broader range
> of life habitats
Mike Butler comments:
>I read Robin's timeframe as billions of years, and his metric as
>something like "the centroid of the biomass".
Yes, I am talking about the whole history of life on earth. And since
we are talking random walks here, a short (<100my) backtrack is nothing.
But my metric is literally "maximum". The maximum biomass individual on
the planet. For some old data, see:
Dale A. Russell (1983) "Exponential Evolution: Implications for
Intelligent Extraterrestrial Life" <i>Adv. Space Res.</i> 3(9):95-103.
By "local tendency" I mean given the median mass of some species at a
point in time, in what direction is the median of the distribution of
specie's median mass at some future point in time. If it is toward
larger masses, there is a local tendency toward larger species. Gould
does explain all this.
Hal Finney writes:
>So ultimately I don't see this point of view as really providing any
>insight into the causes of evolution, since it just pushes the effects
>of natural selection off into another part of the model, where they
>serve to limit the rate at which changes of certain types can occur.
>It doesn't mean that selection isn't important; it is just a matter of
>what you are paying attention to.
I would think empirical data like this would be very helpful in
deciding what to pay attention to.
Robin D. Hanson hanson@hss.caltech.edu http://hss.caltech.edu/~hanson/