The Major Transitions in Evolution is a book written by John Maynard Smith and Eörs Szathmáry (Oxford University Press, 1995).
[5] Maynard Smith and Szathmáry identified several properties common to the transitions: As stated by the authors,[6] this book was aimed at professional biologists and assumes considerable prior knowledge.
[8] The major transitions generally involve the formation of new levels of units of selection, consisting of ensembles of pre-existing entities.
[9] Their work has generated substantial interest and further research into major transitions,[10] including a devoted issue of papers to the subject in 2016 in the journal Philosophical Transactions of the Royal Society B.
[9] Others have noted that the concept of transitions in macroevolutionary history focuses on increases in the levels of complexity, whereas macroevolutionary events can also proceed through simplifications which undo these hierarchical increases in complexity (e.g. multicellular organisms losing adherence genes and so transitioning into unicellular organisms, or the animal and plant lineages with degenerated organelles such as mitosomes).