A paper published by Robert Worden in the Journal of Theoretical Biology in 1995 [r30] was specifically designed to explore the contentious issues around the rate of evolution.** Darwin was a "gradualist" who saw evolution as a slow continuous process - the mainstream view.** Eldridge and Gould challenged this orthodoxy in 1972 by pointing out that in view of the widely observable discontinuities in the fossil record a more precise interpretation would be for evolution to proceed in short bursts covering a few million years followed by long periods of stasis.** [r31]
Worden's paper attempted to provide a resolution for these divergent streams of thinking by phrasing the core issue as one of information gain within a mathematical model.** So just how fast can evolution go, given that:
The rate of evolution of any trait depends on the strength of selection on that trait, where a weak selection pressure results in negligible penetration of a population by a change in the phenotype.
A species can only sustain a limited selection pressure for the obvious reason that when it is too high, the species simply dies out
Worden calculated a speed limit in terms of a measure called the Genetic Information in the Phenotype (GIP), a property of the population measured in bits.*** So the more precisely defined a trait was in a population, the higher the GIP.** Halving the width of the spread of a trait increased the GIP by one bit.**** GIP would thus be indirectly related to the information content of the genome, but always less than it.
Worden found the calculated speed limit to be inconsistent with some versions of Eldridge and Goulds' theory (such as pure species selection) but*compatible with others.
Under the section "Human intelligence and learning" Worden noted that Chomsky had argued that the capacity for language arose de novo in mankind, and in this was supported by Pinker.** Pinker drew attention to the fact that although the human and chimp genotype differed by only about 1%, the difference of about 10MB of information was in his view sufficient to specify a complete language engine.
Worden estimated a total of 350,000 generations since the assumed split 5-7m years ago.** Working on an average number of three children per couple the calculated practical limit on total GIP growth for the human phenotype worked out at most 100,000 bits in total - less than the 10MB quoted by Pinker.
The question Worden considered next was how much of total GIP contributed to the evolution of intelligence, working from the basis that in a typical hominid group the difference in fitness between the least and most intelligent - in terms of survival to successful reproduction - could be assumed to be no larger than 10%.*** Worden calculated that a 10% variation in survival probability contributed a GIP of at most 1/8 bit per generation. So the useful genetic information in the human brain, beyond that in the chimp brain, is limited to 40,000 bits, a shade short of 5KB.
Worden compared the 5KB extra design information in the human brain with a previous estimate of 100KB total GIP in the mammalian brain and concluded that the design information which distinguishes our brains from those of chimps is around 5% of the total.
Reviewing these results Worden noted that 5KB is equivalent to a computer program of around 300 lines:* "Experience suggests that the functionality one can express in 300 lines of program code is very limited; certainly not enough to design a complete facility for language learning and use, unless the underlying computing engine is already very well-adapted for the language task.
"We are led to the conclusion that the main difference between the human brain and other primate brains is one of capacity and power rather than of design complexity; and that our language ability is largely built on some pre-existing mental capacity which other primates have, although they do not use it for language."
Using an information gain of 20,000 bits per million years for a single species as a crude baseline estimate and assuming unchanging reproduction and selection pressures - the total amount of information gain with respect to a specific species since the Cambrian period under the standard model of evolution would be:
Estimated rate of information gain according to the standard evolutionary paradigm:
Thus evolutionary derived GIP available in our era is five times smaller than the theoretical information content represented by the protein encoding parts of the human genome - or 400 times smaller than the information content of the complete genome.**** This factor is a further order of magnitude too small if information gain is considered only from the Cretaceous.*** Another anomaly is highlighted by the fact that approximately 7,000 genes of the (959 celled) nematode C. elegans are shared by humans [r32] *- given the origin of C. elegans dates back from in excess of 600m years whereas human evolution has taken place in the last 5m years. [r34].**
If the difference between a preference for living in the soil, the trees or a castle is derivable by adjusting a set of pre-existing switches in the genotype, then the genotype either displays a considerable amount of really old fashioned luck or a modicum of forethought.
In the absence of any known rigorous selection process in our past how is a genotype generously shared between mice, chimps, humans and even dogs able to provide the capacity for the human brain in a time-frame that in evolutionary terms is the click of a mouse button?**
The rate at which proteins are expressed by genes doesn't help either as the "variation in gene expression between individuals within the species is substantial, relative to the differences between humans and chimpanzees.* For example, one human brain sample differs more from other human samples than the latter differ from the chimpanzee samples."** [r51]
The late Marcel-Paul Schützenberger commented: "Gradualists and saltationists alike are completely incapable of giving a convincing explanation of the quasi-simultaneous emergence of a number of biological systems that distinguish human beings from the higher primates: bipedalism, with the concomitant modification of the pelvis, and, without a doubt, the cerebellum, a much more dexterous hand, with fingerprints conferring an especially fine tactile sense; the modifications of the pharynx which permits phonation; the modification of the central nervous system, notably at the level of the temporal lobes, permitting the specific recognition of speech.
"From the point of view of embryogenesis, these anatomical systems are completely different from one another. Each modification constitutes a gift, a bequest from a primate family to its descendants. It is astonishing that these gifts should have developed simultaneously. Some biologists speak of a predisposition of the genome. Can anyone actually recover the predisposition, supposing that it actually existed? Was it present in the first of the fish? The reality is that we are confronted with total conceptual bankruptcy."* [r56]
Thus both gene mutation and combinatorics offer little theoretical insight into the problem of the gain necessary to support correlated adaptation.****