No Speed Limit For Evolution

Definitions

The rate of evolution can be defined in a number of different ways.

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 technological progress.

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 useful.

Worden

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.

MacKay

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

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 substitution.

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 for?

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 limitation.

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 currently unknown.

  • The rate of development essentially depends on the number and type of experiments that can be simultaneously conducted.

    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 stop.

    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.

Tim Tyler | Contact | http://alife.co.uk/