Major Transitions

A minor evolutionary transition is for example the transition from fins to legs. A major evolutionary transition (a 'landmark transition') in the sense of Eörs Szathmáry and John Maynard Smith is a change in the way information is stored and transmitted. Often this requires a new code (i.e. a new evolutionary system). The largest evolutionary transitions are the transitions from one evolutionary system (or CAS) to another.

• cosmic (physical) evolution
• stellar (chemical) evolution
• mineral (geological) evolution

Then we have an evolutionary phase where inanimate matter evolved into living matter, and the "real" biological evolution began:

• genetic (biological) evolution
• memetic (cultural) evolution
• ..

In the book The Major Transitions in Evolution from John Maynard Smith and Eörs Szathmáry (Oxford University Press, 1995), the authors define a major transition as a major change in the way (genetic) information is organized and transmitted from one generation to the next. The authors focus on biological evolution. The book description says:

"Over the history of life there have been several major changes in the way genetic information is organized and transmitted from one generation to the next. These transitions include the origin of life itself, the first eukaryotic cells, reproduction by sexual means, the appearance of multicellular plants and animals, the emergence of cooperation and of animal societies, and the unique language ability of humans. This ambitious book provides the first unified discussion of the full range of these transitions. The authors highlight the similarities between different transitions--between the union of replicating molecules to form chromosomes and of cells to form multicellular organisms, for example--and show how understanding one transition sheds light on others. They trace a common theme throughout the history of evolution: after a major transition some entities lose the ability to replicate independently, becoming able to reproduce only as part of a larger whole. The authors investigate this pattern and why selection between entities at a lower level does not disrupt selection at more complex levels. Their explanation encompasses a compelling theory of the evolution of cooperation at all levels of complexity. Engagingly written and filled with numerous illustrations, this book can be read with enjoyment by anyone with an undergraduate training in biology. It is ideal for advanced discussion groups on evolution and includes accessible discussions of a wide range of topics, from molecular biology and linguistics to insect societies."

Transitions described in the book
Transition from:	Transition to:	Notes
Replicating molecules	"Populations" of molecules in compartments	Can't observe
Independent replicators (probably RNA)	Chromosomes	RNA world hypothesis
RNA as both genes and enzymes	DNA as genes; proteins as enzymes
Prokaryotes	Eukaryotes	Can observe
Asexual clones	Sexual populations	Evolution of sex
Protists	Multicellular organisms — animals, plants, fungi	Evolution of multicellularity
Solitary individuals	Colonies with non-reproductive castes
Primate societies	Human societies with language, enabling memes	Sociocultural evolution

Maynard Smith and Szathmary identified several properties common to the transitions:

1. Smaller entities have often come about together to form larger entities. e.g. Chromosomes, eukaryotes, sex multicellular colonies.
2. Smaller entities often become differentiated as part of a larger entity. e.g. DNA & protein, organelles, anisogamy, tissues, castes
3. The smaller entities are often unable to replicate in the absence of the larger entity. e.g. Organelles, tissues, castes
4. The smaller entities can sometimes disrupt the development of the larger entity e.g. Meiotic drive (selfish non-Mendelian genes), parthenogenesis, cancers, coup d’état
5. New ways of transmitting information have arisen.e.g. DNA-protein, cell heredity, epigenesis, universal grammar.

28 Steps from Morowitz

The Twenty-Eight Steps from "The Emergence of Everything - How the World Became Complex" Harold J. Morowitz, Oxford University Press, 2002. Morowitz lists Twenty-Eight Steps which lead from elementary particles and their laws to the emergence of human beings. He says "there is some arbitrariness to the number 28. It is a compromise between viewing the major changes and including enough detail to reify the concept of emergence."

The 28 Steps are:

• Origin of the Universe (Steps 1-7: Cosmic Evolution, Physical Sciences, Inorganic & Inanimate Forms, Step 8: Transition (self-replicating molecules: genes)

• Origin of Life (Steps 9-20: Biological Evolution, Life Sciences, Organic Life Forms, Step 21: Transition to memes, language of primate ancestors)

• Origin of Mind and Culture (Steps 22-26: Cultural Evolution, Social Sciences and History, Step 27: Transition to reflective thought)

Emergence of cosmic elements

• 1. The primordium The Big Band and the beginning: The emergence of something from nothing.

• 2. Large-scale structure Galaxy clusters today mirror density fluctuations in the early universe: The emergence of large-scale structures

• 3. Stars Stellar and cosmic evolution through gravity and nucleosnthesis: The emergence of stars

• 4. The Elements A consequence of stellar and cosmic evolution is the emergence of heavier elements through nucleosnthesis and fusion inside stars (and stellar explosions or supernovae): The emergence of elements

• 5. Solar Systems The combination of gravity, nucleosynthesis and stellar explosions in cosmic evolution leads to solar systems, ..

• 6. Planets ..planets and moons made of stellar ash and stardust

• 7. The geosphere Geological evolution of the planetary shell leads to a complex geosphere with continents and islands, i.e. lithosphere (rocks), hydrosphere (water) and atmosphere (gas): the emergence of the geosphere

• 8. The bioshpere The bridge between physical and organic chemistry are self-replicating molecules: the emergence of self-replicating protocells and protogenes

Emergence of Genes: Self-replicating genetic information

• 9. Cells without nucleus: prokaryotes The first self-replicating molecules lead to self-reproducing protocells: the emergence of prokaryotes

• 10. Cells with organelles: eukaryotes Prokaryotic cells without nucleus finally evolved into cells with nucleus: the emergence of eukaryotes, cells with membrane-bounded organelles, the emergence of chromosomes, meiosis and true genes

• 11. Multicellularity Aggregation and differentiation of cells in multicellular organisms can be controlled by genes and offer many advantages: the emergence of multicellularity

Emergence of Animals: Neurons, Digestive Systems and Brains

• 12. Neurons The emergence of rapid cell-to-cell communication of information by electrical and (original) chemical transmission

• 13. Animals The emergence of two subkingdoms of animals, Protostomes and Deuterostomes, which is associated with the evolution of the digestive system with two connected gut openings, one for the input of food and one for the ejection of waste. The names come from the greek and mean: first the mouth (protostomes) second the mouth(deuterostomes, mouth forms later in the development).

• 14. Chordates to Vertebrates The first animals with brains emerge in Step 14. Chordates have, at some stage in their life, a notochord, neural tube or nerve cord, a tail extending past the anus, and bands of muscles that go around the body. Vertebrates are animals with backbones and spinal column (which protect the neural tube and support the body), head and tail end, and cephalization (the centralization of neural organs in the head). The first animals with brains were of course fish and their ancestors.

• 15. Fish According to Morowitz, "until the emergence of insects and amphibians, animal life was almost entirely marine", and "the vertebrate body plan emerged in the evolution of the fish" in the long evolutionary history from "jawless fish to the cartilaginous fish and the bony fish".

Emergence of land Animals: Amphibians, Reptiles and Mammals

• 16. Amphibians The emergence of amphibians is in the traditional sense of the word emergence. The transition from sea to land is connected to the emergence of amphibians, transitional forms between sea and land animals Land animals need lungs for breathing air and limbs for locomotion which evolved from swim bladders and fins, respectively.

• 17. Reptiles (and Dinosaurs) The threat of desiccation and the problem of dehydrating and drying out was solved by the development of hard-shelled eggs and skin made of hard scales: the emergence of eggs and reptiles with scales.

• 18. Mammals Mammals are very intelligent, viviparous, active and warmblooded animals with fur or hair. The emergence of mammals is connected to the emergence of NREM and REM sleep: the emergence of NREM sleep in active, warm-blooded mammals to save energy, and the emergence of REM sleep and Dreams to ensure brain development during the paralyzed and isolated time before birth.

Emergence of Humans: Hominization

• 19. Arboreal mammals Arboreal mammals live in trees and fill the cognitive niche there. The emergence of arboreal mammals is associated with the emergence of grasping hands and stereoscopic vision.

• 20. Primates The emergence of primates is associated with the appearance of complex social groups and group-living.

• 21. The great apes The great apes have a high degree of dexterity (fine motoric skills), increased mental abilities and a complex social order. They mark the emergence of cultural transmission of information through imitation and learning.

Emergence of Memes: Self-replicating memetic information

(Language and Culture)

• 22. Hominids The emergence of bipedalism which freed the hands from locomotion paved the way for tool-using, language and the Homo sapiens.

• 23. Toolmakers The emergence of sophisticated tool-using (chipped stone, hand ax, etc.)

• 24. Language The emergence of human language was a crucial step, language is the base of culture, information transmission and writing systems.

• 25. Agriculture The transition from hunters and gatherers to cattle-breeders and farmers, respectively, marks the boundary between Pleistocene (Ice Age) and Holocene (Recent Age). The emergence of agriculture coincides with the appearance of the first villages, cities and societies and led to technology and urbanization.

• 26. Technology and urbanization Urbanization requires technology, administration and organization. Invention of metallic tools, wheels, steam engines, electricity and other technologies led to rapid progress. The emergence of technology "is a major step between hunter-gatherers and modern civilization".

• 27. Philosophy The emergence of science and philosophy was driven by our desire to understand the fundamental laws of nature.

• 28. The spiritual What kind of emergence is on-going ? Are we in the middle of the emergence of something new, perhaps a new "digital" form of spirit or AI ?

Links

• Nature article from Szathmary and Smith, Szathmary and Smith, The major evolutionary transitions, Nature Vol. 374 (1995) 227-232

• D. W. McSHEA, The minor transitions in hierarchical evolution and the question of a directional bias, J. Evol. Biol. 14 (2001) 502-518

Books

• Harold J. Morowitz, "The Emergence of Everything - How the World Became Complex", Oxford University Press, 2002

• Richard E. Michod, "Darwinian Dynamics: Evolutionary Transitions in Fitness and Individuality", Princeton University Press, 1999

• John Maynard Smith and Eörs Szathmary, "The Major Transitions in Evolution", Oxford University Press, 1997