---
title: "History of evolutionary thought"
chunk: 13/14
source: "https://en.wikipedia.org/wiki/History_of_evolutionary_thought"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:59:38.552937+00:00"
instance: "kb-cron"
---

Microbiology was largely ignored by early evolutionary theory due to the paucity of morphological traits and the lack of a species concept in microbiology, particularly amongst prokaryotes. Now, evolutionary researchers are taking advantage of their improved understanding of microbial physiology and ecology, produced by the comparative ease of microbial genomics, to explore the taxonomy and evolution of these organisms. These studies are revealing unanticipated levels of diversity amongst microbes.
One important development in the study of microbial evolution came with the discovery in Japan in 1959 of horizontal gene transfer. This transfer of genetic material between different species of bacteria came to the attention of scientists because it played a major role in the spread of antibiotic resistance. More recently, as knowledge of genomes has continued to expand, it has been suggested that lateral transfer of genetic material has played an important role in the evolution of all organisms. These high levels of horizontal gene transfer have led to suggestions that the family tree of today's organisms, the so-called "tree of life," is more similar to an interconnected web.
The endosymbiotic theory for the origin of organelles sees a form of horizontal gene transfer as a critical step in the evolution of eukaryotes. The endosymbiotic theory holds that organelles within the cells of eukorytes such as mitochondria and chloroplasts had descended from independent bacteria that came to live symbiotically within other cells. It had been suggested in the late 19th century when similarities between mitochondria and bacteria were noted, but largely dismissed until it was revived and championed by Lynn Margulis in the 1960s and 1970s; Margulis was able to make use of new evidence that such organelles had their own DNA that was inherited independently from that in the cell's nucleus.

=== From spandrels to evolutionary developmental biology ===

In the 1980s and 1990s, the tenets of the modern evolutionary synthesis came under increasing scrutiny. There was a renewal of structuralist themes in evolutionary biology in the work of biologists such as Brian Goodwin and Stuart Kauffman, which incorporated ideas from cybernetics and systems theory, and emphasized the self-organizing processes of development as factors directing the course of evolution. The evolutionary biologist Stephen Jay Gould revived earlier ideas of heterochrony, alterations in the relative rates of developmental processes over the course of evolution, to account for the generation of novel forms, and, with the evolutionary biologist Richard Lewontin, wrote an influential paper in 1979 suggesting that a change in one biological structure, or even a structural novelty, could arise incidentally as an accidental result of selection on another structure, rather than through direct selection for that particular adaptation. They called such incidental structural changes "spandrels" after an architectural feature. Later, Gould and Elisabeth Vrba discussed the acquisition of new functions by novel structures arising in this fashion, calling them "exaptations."
Molecular data regarding the mechanisms underlying development accumulated rapidly during the 1980s and 1990s. It became clear that the diversity of animal morphology was not the result of different sets of proteins regulating the development of different animals, but from changes in the deployment of a small set of proteins common to all animals. These proteins became known as the "developmental-genetic toolkit." Such perspectives influenced the disciplines of phylogenetics, paleontology and comparative developmental biology, and spawned the new discipline of evolutionary developmental biology (evo-devo).

== 21st century ==

=== Macroevolution and microevolution ===

One of the tenets of population genetics is that macroevolution (the evolution of phylogenic clades at the species level and above) was solely the result of the mechanisms of microevolution (changes in gene frequency within populations) operating over an extended period of time. During the last decades of the 20th century some paleontologists raised questions about whether other factors, such as punctuated equilibrium and group selection operating on the level of entire species and even higher level phylogenic clades, needed to be considered to explain patterns in evolution revealed by statistical analysis of the fossil record. Some researchers in evolutionary developmental biology suggested that interactions between the environment and the developmental process might have been the source of some of the structural innovations seen in macroevolution, but other evo-devo researchers maintained that genetic mechanisms visible at the population level are fully sufficient to explain all macroevolution.
. Still others maintain that genetic mechanisms need to be complemented by the physical processes mobilized by the toolkit gene products to account for macroevolutionary transitions 

=== Epigenetic inheritance ===

Epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence. By the first decade of the 21st century it was accepted that epigenetic mechanisms were a necessary part of the evolutionary origin of cellular differentiation. Although epigenetics in multicellular organisms is generally thought to be involved in differentiation, with epigenetic patterns "reset" when organisms reproduce, there have been some observations of transgenerational epigenetic inheritance. This shows that in some cases nongenetic changes to an organism can be inherited; such inheritance may help with adaptation to local conditions and affect evolution. Some have suggested that in certain cases a form of Lamarckian evolution may occur.

=== Extended evolutionary syntheses ===

The idea of an extended evolutionary synthesis extends the 20th-century modern synthesis to include concepts and mechanisms such as multilevel selection theory, transgenerational epigenetic inheritance, niche construction and evolvability—though several different such syntheses have been proposed, with no agreement on what exactly would be included.

== Unconventional evolutionary theory ==

=== Omega Point ===

Pierre Teilhard de Chardin's metaphysical Omega Point theory, found in his book The Phenomenon of Man (1955), describes the gradual development of the universe from subatomic particles to human society, which he viewed as its final stage and goal, a form of orthogenesis.

=== Gaia hypothesis ===