reply to post by Knives4eyes
Funny I was just reading Richard J. Frietas excellent book XENOLOGY: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence,
and Civilization, written in 1979.
Here's a bit from chapter 20.1 - Evolutionary rates:
"A wide variety of different factors operate collectively to increase or decrease the rate of evolution of species on any given planet. It is true
that modern geneticists recognize evolution is primarily a function of genetic variation stored in the species’ general gene pool. Evolution
advances by reshuffling previously accumulated gene types by a process known as "recombination." Nevertheless, the primary and ultimate source of
all genetic variation is mutation.
The average background level of radiation at the Earth’s surface is about 0.12 roentgens/year. About one-third of this is cosmic rays from space.
Among smaller organisms, often as much as 100-1000 times the background is required just to double the natural mutation rate. Among larger organisms,
as little as 3-10 times above background may produce a similar effect over the whole body. It would appear that on Earth today natural radiation
accounts for only a small fraction of all spontaneous mutations.
The situation may have been much different in the past. I.S. Shklovskii and V.I. Krassovskii, two distinguished Russian astrophysicists, have
calculated that Earth may have passed within 10 parsecs of a supernova event perhaps a dozen times since its formation 4.6 eons ago. In each case, the
scientists believe, the intensity of cosmic radiation must have risen at least by a factor of 30. This should have caused an increase of one order of
magnitude in the natural background, which would at least double the mutation rate (and so the maximum rate of evolution) for the largest creatures on
Extraterrestrial creatures inhabiting a planet in the outer Core regions of the Galaxy should experience such a supernova event far more often --
perhaps once every 10 million years. Over the course of geological history more than 500 local supernovae might occur. This would double mutation
rates at regular intervals and keep the pace of evolution high -- especially during the very early stages in the evolution of life on the planet when
gene inventories were still small. We might hypothesize that species "turnover rates" may be significantly higher near Core regions than in the Disk
of the Galaxy...
Many other factors may influence the rate of evolution on other worlds. For example, stellar class of the primary sun may be important. The hottest
stars for which habitable planets are thought to exist are the F5 suns. ...
Another factor which may quicken the pace of evolution is the presence of moons. By raising tides on the planetary shores, natural satellites may
assist chemical mixing and catalysis during the early phases of prebiotic evolution in alien seas....
Planetary factors may also have a decisive effect on the rate of evolution. Perhaps the most influential of these is the relation between land mass
distribution and the diversity of species -- a part of the science of biogeography...
There are many other planetary factors which may affect the rate of evolution. For instance, smaller planets generally may have higher mutation rates
because the levels of background radiation should be higher.
Another major factor that is often overlooked is planetary surface temperature. For any given biochemical basis, the reactions involved in life
chemistry should proceed at faster rates on warm worlds than on colder ones..."
I rest my case.