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Several questions on evolution, and mutation (rate)

Leonard Evens len at math.nwu.edu
Sat Aug 17 21:07:16 EST 1996

Doug Yanega wrote:
> In article
> <Pine.A32.3.91.960815144016.39360B-100000 at flute.aix.calpoly.edu>, Andrew
> Singer <asinger at flute.aix.calpoly.edu> wrote:
> > 3- What is the latest estimate of the age of the earth, and consequestly
> > the earliest life form?
> [snip]
> >
> > 1- Is it impossible to consider that the mutation rate might have
> > decreased to its presently observed rate?
> Mutation rate is only a part of the picture, and you can miss a lot by
> focusing on just that.
> Consider the grand scale of things - we know pretty well that there were at
> least 10 million species on Earth at the turn of the century, over 95% of
> which are arthropods (mostly undescribed). Many folks have intimated that
> via extinction and all, it is probable that these 10 million species are
> only maybe about 10 percent or less of all the species that have ever
> existed. That means that over geologic history, even if you play it
> conservatively, (balancing high/low estimates of modern species with
> various estimates for the number of extinct species) the estimate is about
> 100
> million species have come into being - and the *upper* estimate for how long
> multicellular life has existed is barely 1 billion years. That's an *average*
> of ten new species coming into being in the world every single year.
> Consider that virtually all of those species have been and continue to be
> arthropods, and that the first arthropods date to only about 600 million
> years ago, and the rate is obviously higher. I study insect evolution and
> natural history, and find this entirely plausible. Heck, even if the
> modern species of arthropods were all that had *ever* existed, 10 million
> species in 600 million years is still a pretty hefty rate of speciation -
> evolution is NOT all that slow when the average generation time is
> measured in months or weeks, and once you've got a pool of a few million
> species' worth of raw material...it's no wonder that there may be a few
> dozen new species cropping up every year. Frankly, I expect that a pretty
> large chunk of the present species pool has originated only since the last
> glaciation, a drop in the geological bucket. You also need to bear in mind
> that for most
> organisms, even the tiniest mutation can be enough to lead to a new and
> succesful species, unlike the situation in vertebrates, where it takes a
> truly significant change, in general, before speciation can take place.
> Our human-biased perspective is that of a vanishingly tiny minority. If
> you want to ask questions about evolution, you need to examine the
> planet's dominant life forms - arthropods. Never underestimate the power
> of exponential growth. ;-)
> Cheers,
> Doug Yanega     (dyanega at mail.inhs.uiuc.edu)
> Illinois Natural History Survey, 607 E. Peabody Dr.
> Champaign, IL 61820  USA  (217) 244-6817 fax:(217) 333-4949
> affiliate, University of Illinois Dept. of Entomology
>   http://www.inhs.uiuc.edu:80/~dyanega/my_home.html
> "There are some enterprises in which a careful disorderliness is
>     the true method" - Herman Melville, Moby Dick

One quibble.   As Gould has pointed out the dominant form of life on
Earth is and always has been bacteria.   However, the above remarks are
probably correct as far as multicellular forms of life are concerned.
Note that although we usual call the present era, the age of mammals,
there are only about 4000 species of mammals.   We and our kind are just
a drop in the ocean, although the species Homo Sapiens has certainly
had a dramatic effect on the planet.

Leonard Evens       len at math.nwu.edu      491-5537
Department of Mathematics, Norwthwestern University
Evanston Illinois

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