No Speed Limit For Evolution
The rate of evolution can be defined in a number of
From the perspective of the molecular biologist, the rate of
evolution would be the rate of substitution of alleles in
the population - or some defined sub-section of it.
Other possible metrics for measuring the rate of evolution
with include the possibility of looking at the rate of
beneficial substitutions - or at the rate of
For the purposes of most of this essay, any of these
definitions would be acceptable.
Historical speed limit claims
A number of speed limits for evolution have been claimed in the past:
These tend to deal with "constructive" evolution that does something
Worden argues that evolution results in a low rate of increase
of information in the genome that is actually responsible for
the phenotype - of the order of a few bits per generation.
The limit is actually proportional to the log of the
selection pressure, which is not narrowly bounded in
theory, and organisms with enormous selection pressures exist.
He apparently ignores such effects as cultural inheritance
and genetic engineering - and factors such as the organisms
performing trial and error-based processes themselves. He
also neglects recombination and gamete-level selection processes. His estimate
of the log of the selection pressure in mammals is 3. However, if
you consider gamete selection, and that fact that male gametes
express post-meiosis traits, this seems incorrect. Intra-ejaculate
selection and the resulting segregation distorters allow genetic
changes to take place without organisms dying or failing to reproduce,
and change the situation significantly.
Unfortunately, Worden goes on to assert that his results have some real
world relevance - and then proceeds to draw some highly dubious
conclusions - such as the claim that there is no human "Language
Acquisition Device" - since there was no time available since our
split from our chimpanzee-like ancestors for one to evolve.
Worden's paper should perhaps be retitled: A Speed
Limit On Primitive Evolutionary Processes In Asexual Organisms For Traits
Not Expressed In Gametes.
On one hand, MacKay's paper is rather more convincing than Worden's -
in part because he bothers to analyse recombination, and doesn't spout
nonsense about our ancestors. However, the model analysed is still
pretty primitive. Mating is at random - hardly the case most likely to
lead to rapid evolution - so the conclusions are not realistic.
As with Worden, the possibility of cultural inheritance and genetic
engineering are ignored. This is a speed limit on old-fashioned
evolution by natural selection. This has not been how evolution
actually works for many hundreds of years.
Haldane argued that evolution results in a low rate of
increase of beneficial mutations - because it is difficult
for breeders to simultaneously select all the desired
qualities they are looking for.
This occurs partly because the required genes may not be
found together in the stock, and partly because so many
animals must die - or suffer reduced fertility - before the
required combinations can be generated.
As with Worden and MacKay, Haldane ignores the possibility of evolution
taking place via genetic engineering - which allows
genetic change to occur without death or infertility -
and thus avoids the whole issue of a 'cost' of
A speed limit for evolution?
Since previous commentators have mostly failed to properly
address the issue, the question remains open: is
there an evolutionary speed limit of some kind?
Currently, the pace of technological evolution seems to be
increasing dramatically - how long can that process continue
I can see several possible causes of limits to the speed of
evolution in a population.
The most obvious limit arises from restrictions on the
number and type of experiments which can be concurrently
performed. Such limits could arise through resource
If resource limits exist, they may limit the rate at which
new information about the universe can be generated and
inherited - and thus the rate of technological progress,
and positive evolutionary change.
Most other factors - such as signal propagation speeds
within the population and the number of individuals involved
- appear to be comparatively unimportant.
As far as the speed of evolution as a whole goes,
the limits are less obvious - since the scope of the available
resources appears to be very large - and any upper limits are
- The rate of development essentially depends on the
number and type of experiments that can be simultaneously
Limits in this area could arise due to the universe
being finite in space - or in time - or because of the
existence of barriers that prevent the spread of life
through the universe.
No such limits are known about today - but they may be
discovered by future scientists.
- If the rate of evolution is defined in such a way
that it is measured only in a small area, then there
may be practical limits on the rate at which
information can change in that area.
There is thought to be a limit on the information in any
region of space: the Bekenstein bound.
Similarly, there is a limit on the quantity of information that can
flow into a region of space: the Bekenstein flux bound.
This arises since the information influx into a region is limited by
that region's light cone. There is also a more limiting limit, simply
because not everything in the region's light cone can simultaneously
flow into a region without violating that region's Bekenstein bound:
there will be "fan in" effects that prevent this.
This limits the speed of evolution as measured in a small area - but
this limit seems enormous and very far off.
- If the universe is such that an optimal creature could be produced,
it seems possible that evolution might reach that point - and then
I think the phenomena of brain races will prove to be enduring and
universal - making this outcome unlikely.
- If all living organisms unite, and end natural
selection, then life might form a self-directed
process that might choose not to evolve.
While that may be conceivable in the short term, I
suspect that more advanced aliens would eventually
arrive, and wipe out any such organisms.
No speed limit for evolution in sight
In summary, future cosmological discoveries may
eventually show that a speed limit to evolution as a
whole will eventually be reached at some
point in the distant future.
For the moment, I think we can fairly safely say that
there is no overall speed limit for the evolutionary
process in sight.