.I. theor.
Binl. (1977)*68,
457.-458
Complexity in Organic Evolution Every so often a new addition to evolutionary theory is proposed. Very few of these ever meet with general approval. Another addition has been proposed, linking a general increase in “complexity” with the progress of evolution (Saunders & Ho, 1976). The concept of complexity in evolution h;l~; its pitfalls, as will be seenin the following example. In 1872, the first volume of the Archives de Zoohgie Exphrimentalc ct Ge’ne’rale contained a summary of a publication by Joachim Barrande on tlip “S,ilurian system of central Bohemia” (18711, under the caption, “Proof of paleontological theories by reality”. Among the many curious “disproofs” of Darwinian evolution which appeared in France in the 19th century. this is probably the oddest, but I will not stop to recount the whole story. Ban-an& believed Darwinian evolution required a continual increase in the complexit) of life forms throughout the geological record. “Following the theories,asa resultof the incessantvariations of organized beings,more and more perfect forms will gradually be substitutedfor lehs perfect forms, which are inevitably eliminatedby the efYectof the struggle for existence.In reality, our studies. . . on the evolution of the Trilobites have led usto establishan extreme irregularity in the successive variation< of all the elementsof the crustaceanenvelope.But it is impossiblefor u‘; to recognizethe slightestgradual and constant progressin their apparent organization, throughout the immenseduration of the entire tribe, that is to say, during the whole paleozoic era.”
“according to the theories, animal evolution would have to have taken place in an order determined by the successivedegreesof organization, proceedingfrom the simpleto the complex, that is to say, from the louesl to the highestin the zoological series.” Darwinism was thus “disproved”. This example teaches us the difficulty of treating evolution in terms 01 increasing complexity, as Saunders & Ho (1976) have tried to do in a pi.c\ io:~-, issue of this journal. Organisms can obviously be ordered in terms of compleuity, but such an order frequently does not bear a direct relation to thr process of evolution. In fact, I seethe emphasison complexity, as suggestetl by these authors, to be a possible impediment to clear thinking. Saunders & Ho first tackle what they perceive as an ill-conceived notion ot what “fitness” means. They are certainly correct! We have to recogni?c% 457
458
J.
W.
MCCOY
that E. coli is highly evolved, as were the dinosaurs. Both have fitness--buL only relative to a particular set of environmental and ecological conditions. Obviously there have been many real increasesin complexity in evolution. But the authors seemto neglect the random aspectsof evolution by treating evolutionary history as a simple seriesstarting with a bacterium and ending with mammals. Organic evolution is a process of divergence and wandering rather than an inexorable progression towards increasing complexity, even in free-living forms. It is “forbidden” to retrogress direct/-v, only because01‘ the improbability of precisely undoing a previous modification. Nevertheless, simplification can and does occur by circuitous means. In the long run. natural selection does reward efficiency. Probably everyone will supposethat the examples of astomatous ciliates. parasites, symbionts, cavefish, etc. are exceptional. But consider the evolution of higher plants. The history of the angiospermsmight better be considered in terms of the loss and simplification of parts, rather than in their increased complexity. The duckweed (Lemna), a highly “advanced” plant, is about as simple as an angiosperm can be, while the complexity of a primitive plant such as Magnolia or Liriodendron is evident to all. So convincing is the inverse gradient of complexity, that for decadesthe trend was read largely in reverse. The fossil record gives answerswhich surprise zoologists, on what is “advanced” and what is “primitive ” in the plant kingdom-and in many groups, botanists themselveshave not been able to agree. For that matter. the arguments on the Mesozoa and other “primitive” animals still continue. I am convinced that the neo-Darwinian hypothesis remains an elegant framework to accommodate our observations, without predicting too much. Given a primitive organism and the prescription, “be fruitful and evolve”, we should expect the result to be an experimentation eventually reaching the limits of physical possibility. The blue whale, the sequoia, and the viruses are all approaches to the workable limits of the earth-bound evolutionary process. as it explores organism-space.Both increasesand decreasesin complexity are inevitable, becauseof the random nature of evolution, the continual appearance of new niche-opportunities, and the abstract possibilities allowed by the laws of physics and the nature of this planet. Evolution permits the emergenceof new complexity, but doesnot in any particular casenecessitateit. Section of Botany, Genetics and Physiology, Cornell University, Ithaca, New York 14853, U.S.A. (Received 8 February
1977)
REFERENCES SAUNDERS,
P. T. & Ho,
M.
W.
(1976).
J. theor. Biol. 63, 375.
J. WYNNE
McCoy
Binl. (1977)*68,
457.-458
Complexity in Organic Evolution Every so often a new addition to evolutionary theory is proposed. Very few of these ever meet with general approval. Another addition has been proposed, linking a general increase in “complexity” with the progress of evolution (Saunders & Ho, 1976). The concept of complexity in evolution h;l~; its pitfalls, as will be seenin the following example. In 1872, the first volume of the Archives de Zoohgie Exphrimentalc ct Ge’ne’rale contained a summary of a publication by Joachim Barrande on tlip “S,ilurian system of central Bohemia” (18711, under the caption, “Proof of paleontological theories by reality”. Among the many curious “disproofs” of Darwinian evolution which appeared in France in the 19th century. this is probably the oddest, but I will not stop to recount the whole story. Ban-an& believed Darwinian evolution required a continual increase in the complexit) of life forms throughout the geological record. “Following the theories,asa resultof the incessantvariations of organized beings,more and more perfect forms will gradually be substitutedfor lehs perfect forms, which are inevitably eliminatedby the efYectof the struggle for existence.In reality, our studies. . . on the evolution of the Trilobites have led usto establishan extreme irregularity in the successive variation< of all the elementsof the crustaceanenvelope.But it is impossiblefor u‘; to recognizethe slightestgradual and constant progressin their apparent organization, throughout the immenseduration of the entire tribe, that is to say, during the whole paleozoic era.”
“according to the theories, animal evolution would have to have taken place in an order determined by the successivedegreesof organization, proceedingfrom the simpleto the complex, that is to say, from the louesl to the highestin the zoological series.” Darwinism was thus “disproved”. This example teaches us the difficulty of treating evolution in terms 01 increasing complexity, as Saunders & Ho (1976) have tried to do in a pi.c\ io:~-, issue of this journal. Organisms can obviously be ordered in terms of compleuity, but such an order frequently does not bear a direct relation to thr process of evolution. In fact, I seethe emphasison complexity, as suggestetl by these authors, to be a possible impediment to clear thinking. Saunders & Ho first tackle what they perceive as an ill-conceived notion ot what “fitness” means. They are certainly correct! We have to recogni?c% 457
458
J.
W.
MCCOY
that E. coli is highly evolved, as were the dinosaurs. Both have fitness--buL only relative to a particular set of environmental and ecological conditions. Obviously there have been many real increasesin complexity in evolution. But the authors seemto neglect the random aspectsof evolution by treating evolutionary history as a simple seriesstarting with a bacterium and ending with mammals. Organic evolution is a process of divergence and wandering rather than an inexorable progression towards increasing complexity, even in free-living forms. It is “forbidden” to retrogress direct/-v, only because01‘ the improbability of precisely undoing a previous modification. Nevertheless, simplification can and does occur by circuitous means. In the long run. natural selection does reward efficiency. Probably everyone will supposethat the examples of astomatous ciliates. parasites, symbionts, cavefish, etc. are exceptional. But consider the evolution of higher plants. The history of the angiospermsmight better be considered in terms of the loss and simplification of parts, rather than in their increased complexity. The duckweed (Lemna), a highly “advanced” plant, is about as simple as an angiosperm can be, while the complexity of a primitive plant such as Magnolia or Liriodendron is evident to all. So convincing is the inverse gradient of complexity, that for decadesthe trend was read largely in reverse. The fossil record gives answerswhich surprise zoologists, on what is “advanced” and what is “primitive ” in the plant kingdom-and in many groups, botanists themselveshave not been able to agree. For that matter. the arguments on the Mesozoa and other “primitive” animals still continue. I am convinced that the neo-Darwinian hypothesis remains an elegant framework to accommodate our observations, without predicting too much. Given a primitive organism and the prescription, “be fruitful and evolve”, we should expect the result to be an experimentation eventually reaching the limits of physical possibility. The blue whale, the sequoia, and the viruses are all approaches to the workable limits of the earth-bound evolutionary process. as it explores organism-space.Both increasesand decreasesin complexity are inevitable, becauseof the random nature of evolution, the continual appearance of new niche-opportunities, and the abstract possibilities allowed by the laws of physics and the nature of this planet. Evolution permits the emergenceof new complexity, but doesnot in any particular casenecessitateit. Section of Botany, Genetics and Physiology, Cornell University, Ithaca, New York 14853, U.S.A. (Received 8 February
1977)
REFERENCES SAUNDERS,
P. T. & Ho,
M.
W.
(1976).
J. theor. Biol. 63, 375.
J. WYNNE
McCoy
