From the scala naturae to the symbiogenetic and dynamic tree of life

Abstract

All living beings on Earth, from bacteria to humans, are connected through descent from common ancestors and represent the summation of their corresponding, ca. 3500 million year long evolutionary history. However, the evolution of phenotypic features is not predictable, and biologists no longer use terms such as "primitive" or "perfect organisms". Despite these insights, the Bible-based concept of the so-called "ladder of life" or Scala Naturae, i.e., the idea that all living beings can be viewed as representing various degrees of "perfection", with humans at the very top of this biological hierarchy, was popular among naturalists until ca. 1850 (Charles Bonnet, Jean Lamarck and others). Charles Darwin is usually credited with the establishment of a branched evolutionary "Tree of Life". This insight of 1859 was based on his now firmly corroborated proposals of common ancestry and natural selection. In this article I argue that Darwin was still influenced by "ladder thinking", a theological view that prevailed throughout the 19th century and is also part of Ernst Haeckel's famous Oak tree (of Life) of 1866, which is, like Darwin's scheme, static. In 1910, Constantin Mereschkowsky proposed an alternative, "anti-selectionist" concept of biological evolution, which became known as the symbiogenesis-theory. According to the symbiogenesis-scenario, eukaryotic cells evolved on a static Earth from archaic prokaryotes via the fusion and subsequent cooperation of certain microbes. In 1929, Alfred Wegener published his theory of continental drift, which was later corroborated, modified and extended. The resulting theory of plate tectonics is now the principal organizing concept of geology. Over millions of years, plate tectonics and hence the "dynamic Earth" has caused destructive volcanic eruptions and earthquakes. At the same time, it created mountain ranges, deep oceans, novel freshwater habitats, and deserts. As a result, these geologic processes destroyed numerous populations of organisms, and produced the environmental conditions for new species of animals, plants and microbes to adapt and evolve. In this article I propose a tree-like "symbiogenesis, natural selection, and dynamic Earth (synade)-model" of macroevolution that is based on these novel facts and data.

Reviewers
This article was reviewed by Mark Ragan, W. Ford Doolittle, and Staffan Müller-Wille.

Full text

OPINION Open Access
From the scala naturae to the symbiogenetic and
dynamic tree of life
Abstract
All living beings on Earth, from bacteria to humans, are connected through descent from common ancestors and
represent the summation of their corresponding, ca. 3500 million year long evolutionary history. However, the
evolution of phenotypic features is not predictable, and biologists no longer use terms such as “primitive”or
“perfect organisms”. Despite these insights, the Bible-based concept of the so-called “ladder of life”or Scala
Naturae, i.e., the idea that all living beings can be viewed as representing various degrees of “perfection”, with
humans at the very top of this biological hierarchy, was popular among naturalists until ca. 1850 (Charles Bonnet,
Jean Lamarck and others). Charles Darwin is usually credited with the establishment of a branched evolutionary
“Tree of Life”. This insight of 1859 was based on his now firmly corroborated proposals of common ancestry and
natural selection. In this article I argue that Darwin was still influenced by “ladder thinking”, a theological view that
prevailed throughout the 19th century and is also part of Ernst Haeckel’s famous Oak tree (of Life) of 1866, which
is, like Darwin’s scheme, static. In 1910, Constantin Mereschkowsky proposed an alternative, “anti-selectionist”
concept of biological evolution, which became known as the symbiogenesis-theory. According to the
symbiogenesis-scenario, eukaryotic cells evolved on a static Earth from archaic prokaryotes via the fusion and
subsequent cooperation of certain microbes. In 1929, Alfred Wegener published his theory of continental drift,
which was later corroborated, modified and extended. The resulting theory of plate tectonics is now the principal
organizing concept of geology. Over millions of years, plate tectonics and hence the “dynamic Earth”has caused
destructive volcanic eruptions and earthquakes. At the same time, it created mountain ranges, deep oceans, novel
freshwater habitats, and deserts. As a result, these geologic processes destroyed numerous populations of
organisms, and produced the environmental conditions for new species of animals, plants and microbes to adapt
and evolve. In this article I propose a tree-like “symbiogenesis, natural selection, and dynamic Earth (synade)-model”
of macroevolution that is based on these novel facts and data.
Reviewers: This article was reviewed by Mark Ragan, W. Ford Doolittle, and Staffan Müller-Wille.
Background
In his Autobiography [1], Charles Darwin (1809 - 1882)
presented a self-critical review of his achievements as a
naturalist that revealed much about the character of this
key figure of the evolutionary sciences and other
branches of biology and geology [2-4]. With respect to
the most influential of Darwin’s 16 scientific books, On
the Origin of Species, the author remarked that “Sixteen
thousand copies have now (1876) been sold in England
and considering how stiff a book it is, this is a large sale”
[1]. This judgement is in part due to the fact that the
Origin of Species was not designed by Darwin as a sepa-
rate book; rather, it was published as an Abstract, taken
from a much larger manuscript entitled Natural Selection
[5]. Ironically, Darwin’s major, scheduled “Magnum
opus”with the tentative title Natural Selection never
appeared in print, but the Extract published by the
author in November 1859 in order to establish priority
with respect to his theory of the “preservation of favour-
able variations and the rejection of injurious variations”
became a best- and longseller [6].
The second and more important reason for the “stiff-
ness”of Darwin’sOrigin of Species is attributable to the
almost complete lack of illustrations. In contrast to Dar-
win’s books on botanical and zoological issues, which
contain numerous pictures [2-4], his Abstract published
Correspondence: kut@uni-kassel.de
Institute of Biology, University of Kassel, Heinrich-Plett-Str. 40, D-34109 Kassel,
Germany
Kutschera Biology Direct 2011, 6:33, p. 1--20
http://www.biology-direct.com/content/6/1/33
© 2011 Kutsche ra; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creat ive Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unr estricted use, distribution, and reproduction in
any medium, pro vided the original work i s properly cited.
U. Kutschera
6 (33) 1--20, 2011
Ulrich Kutschera

in 1859 (6th and final edition, 1872) [6,7] contained only
one rather “sterile”diagram, a phylogenetic scheme. This
“tree-like”figure is part of Chapter IV entitled “Natural
Selection”in the first edition [6], and re-named “Natural
Selection; or the Survival of the Fittest”in the 6th and
final version of the “Species book”[7]. It should be noted
that the phrase “survival of the fittest”was borrowed by
Darwin from the philosopher Herbert Spencer (1820-
1903), who was also the first to introduce the word “evo-
lution”sensu phylogenetic development (a term not used
by Darwin in the first edition [6]) into the emerging
biological sciences of the 19th century [5].
With reference to his abstract illustration, Darwin
explained at length the principle of “descent with modi-
fication by means of natural selection”, and concluded,
with his Bible-educated readers in mind, that “On the
view that each species has been independently created, I
can see no explanation of this great fact (i.e., the relat-
edness of all animals and all plants) in the classification
of all organic beings; but, ..., it is explained though
inheritance and the complex action of natural selection,
entailing extinction and divergence of character as we
have seen illustrated in the diagram”[6] p. 100.
Although Darwin made many changes and added
entire sections to the text during the five revisions of his
original version of the Origin [6], one key sentence
remained unchanged: At the end of Chapter IV, the
author wrote, with reference to his tree-like diagram, that
“As buds give rise by growth to fresh buds, and these, if
vigorous, branch out and overtop on all sides many a fee-
bler branch, so by generation I believe it has been with
the great Tree of Life, which fills with its dead and bro-
ken branches the crust of the earth, and covers the sur-
face with its ever-branching and beautiful ramifications”
[6], p. 101; [7], p. 137.
In this article I argue that the metaphorical “Tree of
Life"-statement quoted above was still heavily rooted in
the religious pre-Darwinian “evolutionary ladder-”or
Scala Naturae-thinking of earlier naturalists. In the second
part of this account I show that Darwin’s view of a static,
“Animals and Plants-based Tree of Life”that does not take
into account micro-organisms and endosymbiotic events,
is outdated. Finally, I review evidence indicating that the
dynamic Earth (plate tectonics), geological processes
unknown to Darwin, must be integrated into a more rea-
listic picture of the evolution of life on our ever changing
“planet of the microbes”[5].
From the earliest Moral Tree to the Great Chain
of Being
The Spanish philosopher and theologian Ramon Llull
(1232-1315) was one of the first to publish a tree-like
scheme illustrating the growth and interrelationships of
the basic knowledge of his time. Born into a wealthy
family in Palma, and well educated, he worked as a
teacher in Majorca and Paris. Llull’sdiagramofthe
“apostolic and moral tree”(Figure1)formedpartofa
unified system of knowledge. At the top of this exten-
sively rooted tree, Jesus, the incarnation of the Biblical
God, is depicted, surrounded by the latin words “gloria”
(fame) and “pena”(penalty). The woodcut depicted here
is a modified version of the original that does not show
all the details [8]. In his writings, Ramon Llull argued
that there is no difference between philosophy (i.e., nat-
ural history) and Bible-based theology, and therefore
between reason and faith [8,9]. Hence, even the most
absurd mysteries may be proven by means of logical
inferences and the use of Llull’sArs Magna [9]. This
way of thinking removed all distinctions between natural
(fact-based) truths and supernatural (spiritual) myths.
This “rationalistic mysticism”was taken up by the fol-
lowers of the Spanish theo-philosopher ("Llullists”)and
later evolved into an ideology that was called “Llullism”
[9]. The basic tenet of the “Illuminated Doctor”is illu-
strated in his apostolic tree, which depicts real things
(humans and a tree-like plant), mixed up with a superna-
tural being (Jesus, the son of God, as the crown of the
“tree of knowledge”) [8]. Since Llull also wrote treatises
on medieval natural history (alchemy, botany), and had a
great influence on the mathematician Gottfried W. Leib-
nitz (1646-1716), he is also recognized as a pioneer in
computation theory. However, since he had several reli-
gious visions, and was a convinced Christian, Raymon
Llull, throughout his later life, mixed up facts of nature
and religious imaginations [9].
Although the influence of the “Llullists”may have been
limited, the pre-Christian idea of the Scala Naturae
("Great Chain of Being”) [10-14] is unequivocally related
to the Bible-based scheme depicted in Figure 1. The order
of the static world, between “earth and heaven”,was
shown and thought of as a linear sequence of bodies (from
minerals via plants, animals to man). On top of this hier-
archical arrangement of “created beings”we find the
almighty Biblical God, who, according to Llull, had the fol-
lowing positive attributes: “goodness, greatness, power,
eternity, wisdom, will, virtue, truth, and glory”[9].
One popular version of the Scala Naturae,whichwas
published in 1779 by the Swiss naturalist Charles Bonnet
(1720-1793), is shown in Figure 2. At the base of this ver-
sion of the “Great Chain of Being”are non-living objects
such as minerals and earth, followed by plants, insects,
reptiles (snakes) and mammals. On top of this “natural
ladder”we find the “Orang-Outang”,f
o
llowedby
“L’Homme”(man) [15]. It should be noted that Bonnet,
who discovered the phenomenon of parthenogenesis in
insects, was convinced that species do not change over
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 2

long time periods. In his monograph of 1779 from which
the Scala Naturae is reproduced [15], Bonnet concluded
that there is no visible change in nature, everything
remains largely identical, and species are constant.
Hence, Bonnet and most naturalists of his time were con-
vinced that animals and plants are static essences created
individually by the Biblical God, a religious view that
Darwin attacked and thoroughly refuted [5-7,11-14].
Figure 1 The “Moral Tree”, published posthumously in 1505 in a book authored by Raymon Llull (1232-1315). This Spanish philosopher
and Christian theologian mixed up natural phenomena with supernatural religious dogma and hence became the spiritual father of a medieval
ideology called “Llullism”[part of a woodcut, adapted from ref. 8].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 3

Figure 2 Upper part of the “Great Chain of Being”or Scala Naturae, as published in 1745 by Charles Bonnet (1720-1793) (left
column). On the right side, the title page of the most influential book of Jean Lamarck (1744-1829) and his tree-like scheme of 1809 is shown
[adapted from refs. 15 and 16].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 4

Jean Lamarck and the origin of evolutionary tree-
thinking
The French botanist and zoologist Jean-Baptiste de
Lamarck (1744-1829) was expected by his father to take
a career in the Catholic church. However, the young
naturalist was not inclined to the ministry, and after his
father’s death in 1760 Lamarck quit his Jesuit college to
become a botanist. Later, he made the switch to zool-
ogy, coined key-terms such as “invertebrates”,andpub-
lished new concepts on the relationships between
different groups of animals [16,17].
In his most important book entitled Philosophie Zoolo-
gique [16], Lamarck juxtaposed the “conventional view”,
i.e., the dogma of independent creations of animals (and
plants) as described in the Bible, with his “new opinion":
According to Lamarck [16], there are ongoing sponta-
neous generations of primitive forms of life on Earth.
Later, these non-specialized living beings transformed
into “higher”animals during the history of our planet.
Hence, fifty years before Darwin’sOrigin of Species was
published [6], Lamarck proposed, in 1809, the principle
of the gradual transformation of species and depicted his
“theory of evolution”in a famous tree-like diagram that
is reproduced in Figure 2.
However, a comparison of Lamarck’s original scheme
with Bonnet’sScala Naturae reveals striking similarities:
The “Tableau”of Lamarck, who was an adherent of the
philosophy behind the “Great Chain of Being”[14], is
more “ladder-like”than a true tree with branches and
twigs (Figure 2). In a subsequent book published in 1815,
Lamarck depicted an “Order presuming the formation of
animals in two separate series”[17]. This scheme [repro-
duced in ref. 14] is again more a ladder than a tree. The
author distinguished between three hierarchy levels:
Apathic-, sensible- and intelligent animals, respectively.
Concerning the means by which the structure of an
organism altered over generations, Lamarck proposed his
famous theory that is still known today as the “inheritance
of acquired characteristics”. According to the French
scientist, changes occurred because an animal passed on
to its offspring physiological changes, such as strengthened
muscules it had acquired in its own lifetime, and those
modifications came about in response to its survival needs.
Conversely, the disuse of an organ would cause it to wither
and disappear, which “explained”, how snakes lost their
legs etc. It should be noted that Lamarck’sconceptof
inheritance, which is not supported by empirical evidence
[18], was accepted by Darwin. In addition, Lamarck sug-
gested that species transformations happen according to a
pre-determined plan and that the results have already
been decided by forces he was unable to identify.
Although Lamarck’s theory of the gradual transmuta-
tion of species over long (geological) time periods was
popular until his death in 1829, his ideas encountered
fierce religious and political opposition, notably by
Georges Cuvier (1769-1832). As a result, the achieve-
ments of Lamarck were soon forgotten so that his “prin-
ciple of the gradual transformation of species”was
superseded again by Biblical myths.
Charles Darwin’s Tree of Life and the sterile,
static hierarchy of nature
In a little-known paper of 1855 entitled “On the law
which has regulated the introduction of new species”
[19], Alfred Russel Wallace (1823-1913), the co-disco-
verer of the Darwinian “principle of natural selection”
[20], described a “Tree of Life-concept”referring to
“branching of the lines of affinity, as intricate as the
twigs of a gnarled oak ... and to ..... minute twigs and
scattered leaves”. In an article published one year later,
Wallace described a method of tree-building, which has
recently been discussed in this journal [14].
Charles Darwin’sfamousfirst“Tree of Life"-sketch,
which was supplemented by the phrase “Ithink”
(Figure 3A), was drawn into his “Notebook B”of 1837,
only one year after the junior scientist had returned
from his five-year long voyage on HMS Beagle [5].
Darwin’s sketch appears on page 36 of his “Notebook
B”- the first 35 pages are taken up by considerations
on the “evolutionary thoughts”of his famous grand-
father Erasmus Darwin (1731-1802). The older Darwin
published his revolutionary thoughts on the transfor-
mation of species in his book entitled Zoonomia
(1794). With respect to (endothermic) mammals Eras-
mus Darwin wrote that “... would it be too bold to
imagine that, in the great length of time since the
earth began to exist, perhaps millions of years ... that
all warm-blooded animals have arisen from one living
filament, which the great First Cause endued with ani-
mality, ... and thus possessing the faculty of continuing
to improve by its own inherent activity, and of deliver-
ing down those improvements by generation to its pos-
terity, world without end? ... as the earth and ocean
were probably peopled with vegetable productions long
before the existence of animals ... shall we conjecture
that one and the same kind of living filament is and
has been the cause of all organic life?”[21].
It has been argued that, with respect to Charles Dar-
win’s botanical works, the influence of his grandfather
may have been larger than he later admitted [3]. The
passage cited above suggests that the younger Darwin
developed his famous “I think-sketch”of 1837 (Figure 3
A), at least in part, under the spiritual leadership of his
grandfather Erasmus.
However, what is certain is that for Charles Darwin
the “Tree of Life”was not so much thought of as a
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 5

woody plant, but rather as a coral. As Bredekamp [22]
has documented in detail, Darwin wrote in his “Note-
book B”of 1837 that “The tree of life should perhaps be
called the coral of life”. This view of the “unity of life on
Earth”was in part based on Darwin’shands-onexperi-
ence as a geologist, who had studied coral reefs in nat-
ure. A coral-like organism, later identified as an red alga
(Bossea arbignyana), was collected and preserved by
Darwin (Figure 3 B). This living being resembles the
wide-spread stone coral (Corallium rubrum)(Figure3
C), which served as the living model organism for Dar-
win’s novel concept that has been summarized under
the term “tree-thinking”[23-25].
The only diagram Darwin included into the “sterile”
text of his Origin of Species illustrates the essence of the
“one long argument”developed by the author [6,7].
However, a comparison between the first and last (defi-
nitive) editions of 1859 and 1872, respectively, reveals a
striking improvement of the text: Darwin (1872) had
added a headline entitled “The probable effects of the
action of natural selection through divergence of charac-
ter and extinction, on the descendants of a common
ancestor”to the text so that his discussion of the tree-
like diagram became a separate paragraph in Chapter
IV. On these pages of the Origin,Darwin’sfive“species
theories”that were identified and described for the first
time by Ernst Mayr (1904-2005) [11,12], are apparent
(Figure 4):
1. Descent with modification (Darwin’s definition of
evolution) as a fact of nature versus supernatural acts of
independent species creations, labelled by the author as
religious dogma. 2. The principle of the last common
ancestor of all forms of life (see A in Figure 4). 3. The
theory of gradual, step-by-step species transformations.
4. The multiplication of species over evolutionary time
(thousands of generations) and 5. The principles of nat-
ural (and sexual) selection as the major “driving forces”
for the transformation of species.
In addition to these five “Darwinian species theories”
[for details, see refs. 5, 11, 12], the author discussed the
phenomenon of extinction.AccordingtoDarwin,the
“improved descendant”of any species has the tendency
to supplant and finally exterminate at each stage of evo-
lutionary development “their predecessors and original
progenitor”[6,7]. Finally, it should be noted that Darwin
[6,7] unequivocally proposed a continuum between “spe-
ciation”and the evolutionary development of novel body
plans, processes that were later called “micro- and
macroevolution”, respectively [11,12]. This concept was
described by the British naturalist, with reference to his
famous scheme (Figure 4), in the following words: “In the
diagram, each horizontal line has hitherto been supposed
to represent a thousand generations; but each may repre-
sent a million or more generations ... I see no reason to
limit the process of modification ... to the formation of
genera alone ... new families, or orders, are descended
from two species of the original genus”[7].
Despite these tremendous insights provided by Dar-
win, who was one of the first to replace the “Ladder of
Life”(Figure2)bya“Tree-like concept”[22-25], our
modern view of the biosphere, and the processes that
have brought about the diversity of life as we know it
Figure 3 Charles Darwin’s early sketch of an evolutionary tree (or a coral), drawn in 1837 (A). Marine organism (Bossea arbignyana)
collected by Darwin and classified by him as a coral ("family Corallinae”). Later it was discovered that this “coral-like”inhabitant of sea waters (B)
is a red alga (family Corallinaceae, Phylum Rhodophyta). Red coral (Corallium rubrum), which grows on rocky sea bottom either in the depths or
in dark caverns (C). This wide-spread species, which is found mainly in the Mediterranean Sea, was known to Darwin and possibly served as a
model for his diagram (see Figure 4) [adapted from ref. 22].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 6

today, have advanced to such an extent that Lamarck
and Darwin would hardly understand our current evolu-
tionary concepts. What are the problems with Darwin’s
19th century-ideas about the evolution of life?
First, Darwin [6,7] used old-fashioned terms such as
“perfection, improvement, higher vs. lower (or primitive)
forms of life”etc. that are no longer in use today and
may document relicts of religiously motivated “ladder-
thinking”in his texts. Second, Darwin discussed in none
of his 16 books in any detail the bacteria, although
microbes were already known at that time [2]. In other
words, the scientific work of the British naturalist is
restricted to macro-organisms (animals, plants) to the
exclusion of microbes. His references to “Infusoria”,
“Animalcules”,or“Lower Organisms”[6,7] are confusing
and unclear. Finally, although Darwin experienced a
severe earthquake during his voyage with the HMS Bea-
gle [5], his “species book”[6,7] is based on the implicit
assumption that the Earth is a static planet.
Today it is well established by numerous independent
studies that (1.) bacteria are, based on their collective
protoplasmic biomass, the dominant forms of life, and
by no means “primitive”, (2.) endosymbiotic processes
due to the fusion of ancient microbes have been key
events in the history of life, and (3.) the Earth is not sta-
tic, but dynamic. Our post-Darwinian view of the sym-
biogenetic and dynamic tree of life is described in the
next sections.
Ernst Haeckel’s static trees and the origin of
Monerology
In Germany, the zoologist Ernst Haeckel (1834-1919) was
one of the most prominent popularizers of Darwin’s
ideas, notably of his “theory of descent with modification
by means of natural selection”(i.e., the concepts 1. and 5.
depicted in Figure 4). It should be noted that, in contrast
to many of his colleagues, Haeckel fully acknowledged
the achievements of Jean Lamarck. In one of his popular
books, Haeckel argued that the term “Lamarckism”
should be used to denote the principle of the transforma-
tion of species (i.e., evolution as such, corresponding to
Darwin’s theory no. 1), whereas the word “Darwinism”
should denote the concept of natural selection, one of
the British biologist’s most important insights and
Figure 4 Partial reproduction of the single illustration in Darwin’sOrigin of Species of 1859 (6. ed. 1872). This famous diagram may have
been inspired by corals (or coral-like organisms) as depicted in Figure 3 B, C. Darwin’s five theories are added to the figure (1. to 5.), which
illustrate the transformation and diversification of species, which originate from a common ancestor (A) [adapted from ref. 7].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 7

contributions to the developing evolutionary sciences of
the 19th century [20,26].
With respect to the “Tree of Life”as a coral-like struc-
ture (Figures 3 and 4) it should be remembered that
Haeckel discovered and later described a marine coral
from the Red Sea that was named after his friend and col-
league Charles Darwin. A drawing of this organism (Mono-
xenia darwinii Haeckel 1876) is shown in Figure 5 A. One
of Haeckel’s greatest and most original contributions to
evolutionary biology, his “Gastraea-Theorie”, was based on
his detailed investigations of the development of “Darwin’s
coral”(Monoxenia darwinii). In a journal article published
in 1874 (two years before the organism M. darwinii was
described as a new species), Haeckel concluded that the
two-layered gastrula (i.e., the “Gastraea”or “Urdarmtier”)is
the ancestral form of all animals. This is the essence of
Haeckel’sGastraeatheoryfortheoriginoftheMetazoa
(multicellular animals) [27], a concept that has been corro-
borated by numerous subsequent studies.
InVol.2ofhisGenerelle Morphologie der Organismen
published in 1866, Haeckel outlined his “biogenetic law”,
which the author later described in more detail, in the
following words: “Ontogenesis is the short and fast reca-
pitulation of phylogenesis, controlled through the physio-
logical functions of inheritance (reproduction) and
adaptation (nutrition)”[28]. The significance of Haeckel’s
Figure 5 Adult specimen of “Darwin’s coral”and ontogenesis of Haeckel’s model system. Morphology of the coral Monoxenia darwinii (A),
an organism discovered by Ernst Haeckel in 1873 in the Red Sea and later described by him as a new species, named in honour of Charles
Darwin. The development of M. darwinii is shown in (B), from the fertilized egg (A/B) to the so-called “Becherlarve”(beaker larvae) or gastrula (K/
I). Haeckel coined the term “Gastraea”to denote this phylogenetically conserved stage in animal development [adapted from ref. 27].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 8

“law”(which is today down-sized to a “rule”that permits
exceptions), with respect to the evolution of animals, has
recently been described by Olsson et al. [29]. More
importantly within the context of this article are the
“genealogical trees”drawn and depicted by Haeckel in his
classic monograph. In all of these tree-like diagrams,
German oaks were used as the representative woody
plant. This choice is not surprising. According to the
pre-Darwinian idea of the Scala Naturae (Figure 2), the
one primate of plants, organisms that were ranked in this
Christian medieval hierarchy below the animals, were
oak trees [10]. Since the British scientist Wallace likewise
referred to the “twigs of a gnarled oak”[19],wehaveto
conclude that so-called “ladder-thinking”was still alive in
the minds of Haeckel and Wallace, who published major
books on organismic evolution after the death of Darwin
in 1882.
The most prominent “general”evolutionary tree of
Haeckel, depicting the presumed phylogenetic relation-
ships between animals, plants and various “lower organ-
isms”is reproduced in Figure 6. Three facts should be
highlighted in this context. First, Haeckel [28] argued
that the “Stammbaum der Organismen”(Tree of Life) is
monophyletic. This hypothesis, which corresponds to
Darwin’s“species theory No. 2”(see Figure 4), has
recently been corroborated by D. J. Theobald [30], based
on protein sequence and other molecular data. The
author concluded that “the last universal common
ancestor[LUCA]mayhavecomprisedapopulationof
organisms with different genotypes that lived in different
places at different times”[30]. Second, in contrast to
Darwin [6,7], whose work was based on the 19th-cen-
tury “animal-plant-classification”, Haeckel distinguished
between three “Kingdoms of life":
1. Archephylum vegetabile (Plantae), 2. Archephylum
protisticum (Protista), and 3. Archephylum animale (Ani-
malia). Hence, unicellular “lower organisms”(Protista,
inclusive of the Moneres, i.e., Bacteria), living beings that
were largely ignored by Darwin [6,7], were present in
Haeckel’s view of biodiversity on Earth. Finally, Haeckel
[28] coined the term “Moneres autogonum”to denote
micro-organisms at the common root ("Radix communis
Organismorum”)ofhis“Tree of Life”(Figure 6). How-
ever, it should be noted that on other pages of his books,
Haeckel [28] refers to polyphyletic origins of species. A
discussion of all of Haeckel’s pertinent ideas is beyond
the scope of this article.
The inclusion of microbes that lack a true nucleus
("Moneres autogonum”) into an evolutionary scheme was
a large step towards our modern view of biodiversity.
Today we know that the moneres (Kingdom Bacteria or
Monera) are the dominant forms of life on Earth [31]. It
is obvious that, via the inclusion of the Protista (i.e.,
micro-organisms with and without a nucleus), Haeckel
[28,32] tremendously enlarged our view of life on Earth -
the discipline of “Monerology”(i.e., Bacteriology and
Protozoology) with respect to evolutionary questions
rests to a large extent on the work of this famous Ger-
man biologist. In some of his later writings, Haeckel
mentioned the principle of endosymbiosis (or symbio-
genesis), with reference to the origin of certain green
algae. This topic is discussed in the next section.
Constantin Mereschkowsky’s symbiogenesis
theory and the origin of eukaryotes
In a seminal paper published a century ago in German,
the Russian biologist Constantin Mereschkowsky (1855-
1921) wrote that the most important question of the bio-
logical sciences concerns the origin of species on Earth.
However, according to Mereschkowsky [33], earlier
attempts of Darwin and Haeckel were not successful,
because “atthetimewhentheywereactivenotallthe
facts that are necessary to solve this problem were avail-
able. However, in the meantime novel facts from disci-
plines such as cytology, biochemistry, physiology, notably
of the lower organisms, accumulated so that a new
approach to solve the riddle concerning the origin of liv-
ing beings is justified”[33].
As an alternative to the Darwinian principle of “descent
with modification (i.e., biological evolution) by means of
natural selection”, Mereschkowsky proposed his theory
of symbiogenesis [34,35]. This concept posits that new
organisms, at the level of single cells, occur via symbiotic
events, i.e., by means of the fusion and subsequent coop-
eration of microbes or “Moneren”. Since the origin of the
nucleus was one of Mereschkowsky’s major topics, the
term “symbiogenesis”includes “eukaryogenesis”,i.e.,the
evolutionary development of nucleated cells from non-
nucleated, bacteria-like ancestors. Hence, the original
word “symbiogenesis”should be used instead of the more
recently introduced term “eukaryogenesis”to denote
those processes that led to the origin of the earliest
nucleated (eukaryotic) cells [35].
Based on Mereschkowsky’s insights and those of other
cytologists, L. Margulis proposed the “serial endosymbiosis
hypothesis of the origin of eukaryotic cells”that contain a
nucleus and organelles (mitochondria, chloroplasts) within
their cytoplasm [36,37]. The evidence for this version of
the “symbiogenesis theory”has been summarized and dis-
cussed at length by Kutschera and Niklas [38,39], Cave-
lier-Smith [40-43], Koonin [44-47] an others [48,49]. As E.
Koonin has recently stated in this journal, according to the
well-supported “symbiogenesis sceniario”,asingleendo-
symbiotic event involving the uptake and subsequent
domestication/enslavement of an alpha-proteobacterium
by an archaebacterial host cell led to the generation of the
mitochondria within heterotrophic eukaryotic cells. In a
second step, the uptake of an ancient cyanobacterium, led
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 9

to the origin of plastids (chloroplasts) [44]. These key
events in the history of life on Earth (i.e., serial primary
endosymbioses 1 and 2) occurred ca. 2200 to 1500 and ca.
1500 to 1200 million years ago, respectively, during the
Palaeo- and Mesoproterozoic [38]. At that time, the oxy-
gen content of the oceans was about to rise due to cyano-
bacterial photosynthesis. Gross and Bhattacharya [50] have
proposed that the “birth of eukaryotes, a milestone in the
Figure 6 Reproduction of Ernst Haeckel’s genealogical oak tree depicting the Kingdoms Plantae (plants), Protista (micro-organisms)
and Animalia (animals). Note that the author explicitly pointed out that this general Tree of Life is monophyletic [adapted from ref. 28].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 10

evolution of life on our planet”, was driven by the selective
pressure caused by reactive oxygen species (ROS). These
ROS were light-mediated by-products of the local rise
in O
2
-levels within marine ecosystems during the
Proterozoic.
Although many details concerning the evolutionary
origin of the earliest nucleated, organelle-containing
cells are still a matter of debate [51-53], there is agree-
ment among scientists that symbiogenesis (primary
endosymbiosis) was an early key process in the history
of life [38,39,54]. However, although Mereschkowsky
[33] was the first to clearly point out the importance of
endosymbiotic events during evolution, he did not
accept the “Darwin-Wallace principle of natural selec-
tion”[20] as a driving force for the transformation of
species. This idea prevails to the present day: a number
of “symbiogenesis-researchers”consider endosymbiotic
events and directional natural selection as mutually
exclusive concepts (see ref. 38 for a discussion of this
topic). However, as documented in detail elsewhere
[26,54,55], this view of the natural world is at odds with
numerous observations and experiments. Symbiogenesis,
i.e., primary (and secondary) endosymbioses, combined
with directional natural selection caused by slowly chan-
ging environmental conditions, have been two key pro-
cesses or “driving forces”of organismic evolution, since
the origin of the hypothetical Last Universal Common
Ancestor (LUCA) that gave rise to a heterogeneous
population of aquatic, bacteria-like Proto-cells ca. 3800
million years ago [24,30]. These “factors”of biological
evolution, with respect to the “Tree of Life”,are
depicted in Figure 7.
It should be noted that the relevance of endosymbiotic
events, combined with the process of (bacterial) hori-
zontal gene transfer, has already been discussed with
reference to the “Tree of Life”[23-25,42,56]. However, a
third key process shown in Figure 7, the movements of
tectonic plates (i.e., the dynamic Earth), has been
ignored by these investigators. The significance of these
gradual (sometimes abrupt) changes in the environment
with respect to biological evolution are discussed in the
next section.
Alfred Wegener’s vision of the dynamic Earth,
volcanism and plate tectonics
Four decades ago, J. C. Maxwell summarized the concept
of the dynamic Earth in the following words: “The earth’s
surface, in the context of geologic time, may be likened
to a boiling vat of maple syrup. The crust, with its high-
standing continents, is analogous to the scum which rises
from boiling syrup, coalesces, drifts apart, and rejoins in
different patterns on the surface of the convecting liquid.
The earth’s crust is a similarly thin scum of relatively
light rocks ‘floating’on the mantle, a zone of heavier
materials extending halfway to the earth’scenterand
overlying the inner metallic core. By some cosmic acci-
dent the earth has been endowed with a magnetic field,
apparently for much of its 4.5-billion-year history.
Figure 7 Symbiogenesis, natural selection, and the dynamic Earth as key processes that caused biological evolution. The Last Universal
Common Ancestor (LUCA) evolved into the earliest self-replicating proto-cells (ancient microbes) ca. 4000 to 3500 million years ago. Over the
subsequent eons, these archaic microbes evolved into numerous bacterial ecotypes that today inhabit every micro-niche where organic
molecules (or light) are available. Moreover, these micro-organisms gave rise to larger, eukaryotic cells via symbiogenesis (primary
endosymbiosis). These nucleated cells further evolved into multicellular organisms, such as algae, fungi, animals and plants.
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 11

Changes in the field with respect to a point on the sur-
face are recorded by successively formed sequences of
rock. Analysis of these ancient magnetic fields gives con-
vincing evidence of extensive differential movements in
the earth’s crust. The composition of the crust and the
forces which cause its deformation are apparently deter-
mined by gravitational and thermal instabilities within
the outer few hundred kilometers of the mantle. Tem-
perature within the earth increases downward at a rate
exceeding the adiabatic gradient for the upper few hun-
dred kilometers, hence this outer zone is intrinsically
unstable. Vertical movements, once initiated, tend to be
self-propagating. These instabilities may give rise to lat-
eral and vertical movements approximating convecting
currents in liquids. Rising currents have apparently
occurred largely in oceanic areas, bringing new mantle
material to the surface in the oceans and sweeping older
oceanic rocks towards and perhaps beneath the high-
standing continents. The great mountain ranges which
border many continents are believed to be related in
some way to the convective overturn of rocks in the
earth’s crust and upper mantle”[57]. This description,
published in 1971, was a concise summary of a long ser-
ies of articles and books that originated in 1858.
In this year, the French geographer Antonio Snider-Pel-
legrini (1802-1885) published two imaginative maps
depicting the continents of the Earth, “before and after
separation”[58]. This early outline of the idea of continen-
tal drift, and hence the dynamic Earth (Figure 8 A), did
not convince the geologists of the time, because Snider-
Pellegrini’s speculations were largely based on Biblical
myths and only on few scattered empirical data. As a
result, the old concept of a static Earth, the “geological
basis”of all views of the “hierarchy and organization of life
on our planet”, as depicted in ladders and trees, from
Charles Bonnet’sScala via Darwin’sDiagram to Ernst
Haeckel’sOak, prevailed (Figures 1 to 6).
Seven decades after Snider-Pellegrini’s account was pub-
lished, the last (definitive) edition of Alfred Wegener’s
(1880-1930) book on The Origin of the Continents and the
Oceans [59] appeared in print. In this monograph of 1929,
the German scientist summarized a long list of empirical
evidence for a novel fact-based theory of continental drift
that overshadowed the earlier, Bible-inspired speculations
of the French geographer. In essence, Wegener stated that
the isolated continents as we observe them today were
once united and formed a super-continent. This giant
proto-land mass ("Pangaea”) may have covered up to 50%
of the surface of our planet and was surrounded by one
large ocean ("Panthalassa”). Due to “continental drift”via
mechanisms inexplicable to Wegener, the land masses
finally reached, in the course of millions of years of steady
motion, the position they have today. Despite Wegener’s
inability to explain the physical processes that may have
caused the drift of these large land masses, the author pro-
posed that the formation of mountains, via compressive
forces, the occurrence of earthquakes, and volcanism are
consequences of continental drift [59]. Today it is well
established that Wegener was right (Figures 8 B, C; 9).
Only a few years before J. C. Maxwell published his
summary of the “Dynamic Earth”quoted above, the
concept of plate tectonics was proposed. This unifying
theory of geology states that the Earth’s outer rigid shell
(i.e., the lithosphere) is broken into more than a dozen
giant, rigid plates that float on the hot, ducile mantle
(i.e.,theasthenosphere)likepiecesoficeonalake.
Most of the Earth’s documented history results from
plates rifting into pieces to form new ocean basins.
When they converge back together, they can form
mountains and large continents (Figure 8 C). As shown
in Figure 9, the rigid lithospheric plates differ in size
and their direction of internal heat-driven motion. Some
pieces of the outer crust, such as the North American
Plate, carry continents and attached pieces of the ocean
floor. Other parts of the lithosphere, such as the Pacific
Plate, are entirely covered by oceans and are made of
oceanic crust. For instance, in the area of San Francisco
(California) and elsewhere, the North American and
Pacific Plates are pushed at each other, and the sponta-
neous release of pressure causes abrupt, short plate
movements, so-called “earthquakes”(Figure 8 B). These
rapid, unpredictable geologic events may have devastat-
ing secondary effects. For instance, the 2011 Sendai 9.0
megathrust earthquake that occurred on March 11 off
the coast of Japan triggered destructive tsunami waves
with highs of up to 12 m. These masses of sea water
have travelled up to 10 km inland, destroyed the terres-
trial landscape, and caused thousands of deaths. Fre-
quently, such devastating earthquakes occur along the
so-called “Pacific Ring of Fire”, stretching from New
Zealand, along the eastern edge of Asia north across the
Aleutian Islands of Alaska and south along the coast of
NorthandSouthAmerica.The“Ring of Fire”,which
has 452 volcanoes, is a direct consequence of plate tec-
tonics and hence the movements/collisions of crustal
plates [60].
What is the significance of the theory of plate tec-
tonics for the geological sciences? Theodosius Dobz-
hansky (1900-1975) once said that “Nothing in biology
makes sense except in the light of evolution”[61].
Accordingly, earth scientists may conclude that “Not
much in geology makes sense except in the light of
plate tectonics”. In other words, the theory of plate tec-
tonics is the unifying principle of historical geology.
The consequences of the internal heat-driven move-
ments of tectonic plates for the evolution of life on
Earth, as well as the “Tree-models”depicting this pro-
cess, are obvious: new habitats are created and existing
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 12

Figure 8 Scheme depicting the idea of continental drift as envisioned by A. Snider-Pellegrini in 1858 (A). This concept was re-discovered
and supported by empirical evidence by A. Wegener in 1929. Decades later, the theory of plate tectonics was deduced. Plate tectonics accounts
for most of the planet’s earthquakes, which may result in deep cracks in the Earth’s surface (B) and the formation of mountains as a result of
horizontal compression of the crust (C) [adapted from ref. 58 and from photographs of the US Geological Survey, 1938].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 13

ones are re-modelled or destroyed by these geologic
events (Figure 7). Major mass extinctions, such as those
that occurred 251 and 65 million years ago, respectively,
were at least in part caused by massive volcanic erup-
tions and hence the dynamic Earth [54,60].
In a recent publication it was documented that the
break-up of the super-continent Pangaea (which existed
from the Perminan into the Jurassic, ca. 299 to 200 mil-
lion years ago), due to plate tectonics, accounts for the
evolutionary diversification of many groups of animal,
such as dinosaurs, mammals and the land leeches of
Madagascar [62]. Another example for the role of plate
tectonics as driving force for speciation are amphibious
tetrapods, such as salamanders. A detailed analysis of
numerous collected specimens of the four-toed Asian
salamanders (family Hynobiidae) revealed that the 46
biospecies were “created”as a result of plate tectonics.
About 110 million years ago, much of Asia was a low-
lying humid region where salamanders of all varieties
existed. A series of geologic events, which resulted in
the lifting up of the Tibetan Plateau and mountain-
building led to the isolation of sub-populations that
evolved, over millions of years, into separate,
geographically isolated species [63]. Hence, the dynamic
Earth must be interpreted as a major factor that drove
the evolutionary diversification of many macro-organ-
isms on our planet [64,65] (Figures 8, 9). It should be
mentioned that wildfires, which have a large impact on
the distribution and diversification of plants and ani-
mals, are regularly caused by massive volcanic eruptions
(Figures 10, 11). These secondary consequences of plate
tectonics may also have been an important cause for the
extinction of the dinosaurs that occurred 65 million
years ago [54,61,66].
Finally, we have to address the question as to the con-
sequences of volcanism (and the associated wildfires) on
the evolutionary patterns of micro-organisms, such as
bacteria, soil amoebae and unicellular algae (diatoms
etc.) [67]. One case study may illustrate this topic. The
eruption of Mount St. Helens in southwest Washington,
USA, on May 18, 1980 released superheated steam and
gases. Moreover, this catastrophic event resulted in pyr-
oclastic flows, landslides, mudflows, and ash fall. As a
result, novel habitats were formed, whereas old ones
were re-structured, scoured, or eliminated [68]. Six
years after the eruption, some aquatic habitats were
Figure 9 Model of the Earth’s surface, which is broken into drifting fragments, the so-called tectonic plates.The“lubricant”of plate
movements is liquid water. In this picture, the South American and African plates are highlighted. In addition, the moon, a solid satellite without
water and plate movements, is shown in the upper left quarter. Red lines: Regions where volcanic eruptions occur frequently [adapted from
ref. 75].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 14

analyzed with respect to the presence of micro-organ-
isms. The results show that species richness and micro-
bialdiversitywereverylowatthemostheavily
disturbed sites around the cool volcano, documenting a
large mass extinction event at the “micro-scale”[69].
However, more work on other volcanic sites is necessary
to corroborate these results. These data document that
volcanic eruptions (and wildfires) lead to a temporary
“sterilisation”of the affected aquatic and terrestrial habi-
tats and hence to the destruction of most of the micro-
organisms that existed there before the catastrophic
event occurred (Figures 10, 11). The patterns of re-colo-
nization by microbial communities and the resulting
evolutionary diversifications are not yet explored in
detail.
Conclusions: The tree-like Synade-model of
macroevolution
In a recent analysis of Charles Darwin’s“species book”it
was documented in detail that the British naturalist and
theologian used Biblical phrases such as “He who ...”
throughout his Origin of Species [70]. Darwin’skey
metaphor for the principle of descent with modification,
combined with his theory of the last common ancestor,
was the “great Tree of Life”[6,7]. In this context I
would like to add that the symbol of Trees appears in
the creation myth of the Old Testament (Genesis 2, 9):
“And the Lord God made all kinds of trees grow out of
the ground - trees that were pleasing to the eye and
good for food. In the middle of the garden were the tree
of life and the tree of the knowledge of good and evil”.
In this article I have shown that, from the earliest,
Bible-inspired “Moral Tree”(Figure 1), via the hierarchi-
cal Scala Naturae, to Darwin’s and Haeckel’s static trees
(or corals) of life, the old, Biblical “woody plant-model”
evolved by descent with modification: The Christian
“ladder-thinking”was gradually replaced by the post-
Darwinian ("Haeckelian”)atheistic“oak-tree-concept”
that included animals, plants and micro-organisms
(Figure 6). However, neither Darwin nor Haeckel took
the principle of symbiogenesis (primary endosymbiosis)
into account, because this evolutionary process - the
“creation”of more complex eukaryotic cells via the
fusion of archaic microbes and the subsequent coopera-
tion of the partners - was largely unknown at that time.
It should be stressed that Haeckel mentioned symbioge-
netic events in the context of the origin of green algae
and land plants [34], but the German biologist failed to
integrate this insight into his general picture of the evo-
lution of life on Earth.
Moreover, the trees of Darwin and Haeckel are “sta-
tic”, based on their implicit assumption of an Earth sur-
face that does not display significant movements.
Unfortunately, even the “architects”of the Synthetic
Figure 10 The massive 1872 eruption of the Vesuvius, the only active volcanoe in mainland Europe (Italy). Vesuvius is most famous for
the 79 A. D. eruption that destroyed the Roman cities of Pompeii and Herculaneum. Plate tectonics is the major cause for these violent
eruptions, which document ongoing magmatic processes driven by heat from the radioactive decay within the Earth [adapted from an
anonymous painting, ca. 1880].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 15

Theory of Biological Evolution developed between 1937
and 1950, Theodosius Dobzhansky (1900-1975), Ernst
Mayr (1904-2005), Julian Huxley (1887-1975), George
G. Simpson (1902-1984), Bernhard Rensch (1900-1990),
and G. Ledyard Stebbins (1906-2000) ignored symbioge-
netic events and the dynamic Earth [54,61,71-73]. These
fundamental processes were, like the insights gained
from the disciplines of evolutionary developmental biol-
ogy ("Evo-Devo”) and geology (mass extinctions), inte-
grated into the “Expanded Synthesis”published in 2004
[54,74]. Due to this steady growth of our “Tree of mod-
ern evolutionary knowledge”, the scientific discipline of
evolutionary biology has been defined as a “system of
theories”that explains the various aspects of those pro-
cesses that Charles Darwin described as “descent with
slight and successive modifications”[6,7].
W. F. Doolittle [23-25,56] and others [52] have
recently argued that the construction of a universal Tree
of Life, as originally suggested by Darwin [6,7] and
Haeckel [28] (Figures 4 and 6), may be difficult to
achieve. These authors based their judgement on two
facts. First, in prokaryotes (bacteria, cyanobacteria),
which comprise the majority of life forms on Earth and
were the sole organisms during ca. 2/3 of the early his-
tory of organismic evolution on this planet, lateral gene
transfer (the exchange of genetic information between
extant microbes) occurs regularly. Second, endosymbio-
tic events, and hence the fusion of microbial lineages,
should be taken into account when tree-like models are
drawn [51].
In my view, symbiogenesis, denoted here as early pri-
mary endosymbiotic processes that gave rise to the
Figure 11 Volcanic eruptions can ignite wild fires that result in the destruction of the vegetation, soil micro-organisms, and less
mobile animals. In this drawing, Zebras and other mammals are depicted that are just about to escape from a severe wild fire [adapted from a
drawing of H. Harder, 1912].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 16

organelle-bearing eukaryotic cells during the Protero-
zoic, and subsequent, secondary endosymbiotic events
that are responsible for the origin of the majority of the
unicellular marine phytoplanktonic organisms
[38,39,54,74], were key events during the history of life.
Moreover, plate tectonics and hence the dynamic Earth
must be incorporated into our view of any tree-like
reconstruction of biological evolution. Based on the
facts summarized in this article and elsewhere [5,62,75]
I propose that symbiogenesis, (directional) natural selec-
tion, and the dynamic Earth were key processes that
must be viewed as three important “driving forces”of
organismic evolution (Figure 7).
A more precise “tree-like”version of this “synade-
model”of macroevolution, which takes into account all
organisms on Earth (i.e., members of the Kingdoms Bac-
teria, Protoctista, Animalia, Fungi, and Plantae) is
depicted in Figure 12. The oldest branch of living
beings, the Bacteria (syn. Kingdom Monera), represent
more than 50% of the protoplasmic biomass on Earth
[31]. They are, as pathogens and/or symbionts, impor-
tant “factors”in the evolution of all Eukaryotes. Hence,
ancient and recent prokaryotic microbes are included as
“background organisms”[31,67]. In addition, a scheme
of our planet depicting the centre of the Earth is shown
in Figure 12. Without internal heat, which is primarily
caused by the energy given off as a result of the radioac-
tive decay of uranium, our “blue planet”would probably
be as static as the moon (Figure 9).
According to the “tree-like”synade-model of macroe-
volution proposed here (Figures 7 and 12), all extant
and extinct organisms have, through the eons of geolo-
gical time, benefited from the dynamic Earth due to the
creation of early terrestrial land masses within giant
marine habitats, and the subsequent formation of moun-
tains, deserts, freshwater ecosystems, and deep oceans
[64,75]. On the other hand, massive volcanic eruptions,
which are “side effects”of plate tectonics, have caused
(or significantly contributed to) several mass extinctions
during Earth’s history. Hence, the mobile tectonic plates
led to the destruction of countless living beings on this
“blue planet of the microbes”.Finally,itshouldbe
stressed that micro-organisms, the “unseen majority”
[31] that Darwin largely ignored [76,77], are the true
“winners”in the ongoing, ca. 3.500 million-year-long
“struggle for life”on our ever changing, dynamic Earth
[5,59-62,78-86].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 17

Figure 12 The tree-like “Synade-model of macroevolution”, taking into account all five Kingdoms of life on Earth. According to this
theory, symbiogenesis (primary and secondary endosymbiotic events), (directional) natural selection, and the (internal heat-driven) dynamic Earth
were and still are key drivers of macroevolution on our “planet of the bacteria”[adapted and modified from ref. 62].
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 18
Acknowledgements
I thank the Alexander von Humboldt-Foundation (Bonn, Germany) for
financial support (AvH fellowship Stanford/USA, 2010-2011, to U. K.) and The
Leverhulme Trust (London, United Kingdom) for payment of the article-
processing charges as part of the project “Questioning the Tree of Life”.
Authors’contributions
The author planned and wrote the paper.
Received: 11 January 2011 Accepted: 30 June 2011
Published: 30 June 2011
References
1. Barlow N, (ed.): The Autobiography of Charles Darwin London: Collins; 1958.

2. Kutschera U, Niklas KJ: Evolutionary plant physiology: Charles Darwin’s
forgotten synthesis. Naturwissenschaften 2009, 96:1339-1354.
3. Kutschera U, Briggs WR: From Charles Darwin’s botanical country-house
studies to modern plant biology. Plant Biol 2009, 11:785-795.
4. Kutschera U, Elliott JM: Charles Darwin’s observations on the behaviour of
earthworms and the evolutionary history of a giant endemic species
from Germany, Lubricus badensis (Oligochaeta: Lumbricidae). Appl
Environm Soil Sci 2010, 2:1-11.
5. Kutschera U: Charles Darwin’sOrigin of Species, directional selection, and
the evolutionary sciences today. Naturwissenschaften 2009, 96:1247-1263.
6. Darwin C: On the Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life London: John Murray;
1859.
7. Darwin C: The Origin of Species by Means of Natural Selection, or the
Preservation of Favoured Races in the Struggle for Life. 6 edition. London:
John Murray; 1872.
8. Kearney H: Science and Change 1500-1700 New York and Toronto: World
University Library; 1971.
9. Bonner A, (ed.): Doctor Illuminatus: A Ramon Lull Reader Princeton: Princeton
University Press; 1985.
10. Bynum WF: The Great Chain of Being after forty years: An appraisal.
History of Science 1975, 13:1-28.
11. Mayr E: The Growth of Biological Thought. Diversity, Evolution, and Inheritance
Cambridge, Massachusetts: Harvard University Press; 1982.
12. Mayr E: What Evolution Is New York: Basic Books; 2001.
13. Junker T, Hoßfeld U: Die Entdeckung der Evolution. 2 edition. Auflage.
Darmstadt: Wissenschaftliche Buchgesellschaft; 2009.
14. Ragan MA: Trees and networks before and after Darwin. Biol Direct 2009,
4:43.
15. Bonnet C: In Oeuvres d’histoire naturelle et de philosophie. Volume 1.
Neuchatel; 1779.
16. Lamarck J-B: Philosophie Zoologique, ou Exposition des Considérations relatives
àl’Histoire naturelle des Animaux Paris: Dentu et ‘l Auteur; 1809.
17. Lamarck JB: Histoire Naturelle des Animaux sans Vertèbres Paris: Verdière; 1815.
18. Koonin EV, Wolf YI: Is evolution Darwinian or/and Lamarckian? Biol Direct
2009, 4:42.
19. Wallace AR: On the law which has regulated the introduction of new
species. Ann Mag Nat Hist (n s) 1855, 16:184-196.
20. Kutschera U: Darwin-Wallace principle of natural selection. Nature 2008,
453:27.
21. Darwin E: In Zoonomia; or the Laws of Organic Life. Volume 1 to 3. Boston:
Thomas & Andrews; 1794.
22. Bredekamp H: Darwins Korallen Die frühen Evolutionsdiagramme und die
Tradition der Naturgeschichte Berlin: Verlag Klaus Wagenbruch; 2005.
23. Doolittle WF: The practice of classification and the theory of evolution,
and what the demise of Charles Darwin’s tree of life hypothesis means
for both of them. Phil Trans R Soc Lond B: Biol Sci 2009, 364:2221-2228.
24. Doolittle WF: Phylogenetic classification and the universal tree. Science
1999, 284:2124-2128.
25. Doolittle WF: The attempt on the life of the Tree of Life: science,
philosophy and politics. Biol Philos 2010, 25:455-473.
26. Kutschera U: A comparative analysis of the Darwin-Wallace papers and
the development of the concept of natural selection. Theory Biosci 2003,
122:343-359.
27. Haeckel E: Die Gastraeatheorie, die phylogenetische Classification des
Thierreiches und die Homologie der Keimblätter. Jena Z Naturwiss 1874,
8:1-55.
28. Haeckel E: Generelle Morphologie der Organismen. Allgemeine Grundzüge der
organischen Formen-Wissenschaft, mechanisch begründet durch die von
Charles Darwin reformierte Descendenztheorie. Bd. 1 und 2 Berlin: De Gruyter;
1866.
29. Olsson L, Levit GS, Hoßfeld U: Evolutionary developmental biology: its
concepts and history with a focus on Russian and German
contributions. Naturwissenschaften 2010, 97:951-969.
30. Theobald DL: A formal test of the theory of universal common ancestry.
Nature 2010, 465:219-222.
31. Whitman WB, Coleman DC, Wiebe WJ: Prokaryotes: the unseen majority.
Proc Natl Acad Sci USA 1998, 95:6578-6583.
32. Haeckel E: Das Protistenreich. Eine populäre Übersicht über das Formengebiet
der niedersten Lebewesen. Mit einem wissenschaftlichen Anhang: System der
Protisten Leipzig: Ernst Günther; 1878.
33. Mereschkowsky C: Theorie der zwei Plasmaarten als Grundlage der
Symbiogenesis, einer neuen Lehre von der Entstehung der Organismen.
Biol Zentralblatt 1910, 30:278-303.
34. Sapp J, Carrapico F, Zolotonosov M: Symbiogenesis: The hidden face of
Constantin Merezhkowsky. Hist Phil Life Sci 2002, 24:413-440.
35. Geus A, Höxtermann E: Evolution durch Kooperation und Integration. Zur
Entstehung der Endosymbiosetheorie in der Zellbiologie. Basilisken-
Presse, Marburg; 2007, (Hg).
36. Margulis L: Symbiosis in Cell Evolution. Microbial Communities in the
Archean and Proterozoic Eons. 2 edition. New York: W. H. Freeman & Co;
1993.
37. Margulis L: Archaeal-eubacterial mergers in the origin of Eukarya:
Phylogenetic classification of life. Proc Natl Acad Sci USA 1996,
93:1071-1076.
38. Kutschera U, Niklas KJ: Endosymbiosis, cell evolution, and speciation.
Theory Biosci 2005, 124:1-24.
39. Kutschera U, Niklas KJ: Macroevolution via secondary endosymbiosis: a
Neo-Goldschmidtian view of unicellular hopeful monsters and Darwin’s
primordial intermediate form. Theory Biosci 2008, 127:277-289.
40. Cavalier-Smith T: Membrane heredity and early chloroplast evolution.
Trends Plant Sci 2000, 5:174-182.
41. Cavalier-Smith T: Deep phylogeny, ancestral groups, and the four ages of
life. Philos Trans R Soc Lond B: Biol Sci 2010, 365:111-132.
42. Cavalier-Smith T: Origin of the cell nucleus, mitosis and sex: roles of
intracellular coevolution. Biol Direct 2010, 5:7.
43. Cavalier-Smith T: Rooting the tree of life by transition analysis. Biol Direct
2006, 1:19.
44. Koonin EV: On the origin of cells and viruses. Primordial virus world
scenario. Ann NY Acad Sci 2009, 1178:47-64.
45. Koonin EV: The origin and early evolution of eukaryotes in the light of
phylogenomics. Genome Biol 2010, 11:209.
46. Koonin EV, Wolf YI: The fundamental units, processes and patterns of
evolution, and the Tree of Life conundrum. Biol Direct 2009, 4:33.
47. Yutin N, Wolf MY, Wolf YI, Koonin EV: The origins of phagocytosis and
eukaryogenesis. Biol Direct 2009, 4:9.
48. Bowman JL, Floyd SK, Sakakibara K: Green genes - comparative genomics
of the green branch of life. Cell 2007, 129:229-234.
49. Knoll AH: Life on a Young Planet. The First Three Billion Years of Evolution
on Earth Princeton and Oxford, Princeton University Press; 2003.
50. Gross J, Bhattacharya D: Uniting sex and eukaryote origins in an
emerging oxygenic world. Biol Direct 2010, 5:53.
51. Davidov Y, Jurekvitch E: Predation between prokaryotes and the origin of
eukaryotes. BioEssays 2009, 31:748-757.
52. Lane CE, Archibald JM: The eukaryotic tree of life: Endosymbiosis takes its
TOL. Trends Ecol Evol 2008, 23:268-275.
53. Lane N, Martin W: The energetics of genome complexity. Nature 2010,
467:929-934.
54. Kutschera U, Niklas KJ: The modern theory of biological evolution: an
expanded synthesis. Naturwissenschaften 2004, 91:255-276.
55. Bell G: Selection: the mechanism of evolution New York: Chapman and Hall;
1997.
56. Doolittle WF, Bapteste E: Pattern pluralism and the tree of life hypothesis.
Proc Natl Acad Sci USA 2007, 104:2043-2049.
57. Maxwell JC: Dynamic Earth. J Appl Physics 1971, 42:1467.
58. Snider-Pellegrini A: La Création et ses mystères dévoilés Franck et Dentú,
Paris; 1858.
59. Wegener A: Die Entstehung der Kontinente und Ozeane. 4. Auflage
Braunschweig, F. Vieweg & Sohn; 1929, (1. Auflage 1915).
60. Skinner BJ, Porter SC: The Dynamic Earth: An Introduction to Physical
Geology. 5 edition. New York: John Wiley & Sons; 2003.
61. Gould SJ: The structure of evolutionary theory Cambridge, Massachusetts,
Harvard University Press; 2002.
62. Kutschera U: Symbiogenesis, natural selection, and the dynamic Earth.
Theory Biosci 2009, 128:191-203.
63. Zhang P, Chen YQ, Zhou H, Lin YF, Wang XL, Papenfuss TJ, Wake DB,
Qu LH: Phylogeny, evolution, and biogeography of Asiatic Salamanders
(Hynobiidae). Proc Natl Acad Sci USA 2006, 103:7360-7365.
64. Nield T: Supercontinent. Ten billion years in the life of our planet Cambridge,
Harvard University Press; 2007.
65. Steinberger B: Reconstructing earth history in three dimensions. Science
2008, 322:866-868.
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 19

66. Whelan RJ: The Ecology of Fire Cambridge, Cambridge University Press; 1995.
67. Kutschera U: Plant-associated methylobacteria as co-evolved
phytosymbionts. A hypothesis. Plant Signal Behav 2007, 2:74-78.
68. Franklin JR, Mac Mahon JA, Swanson FJ, Sedell JR: Ecosystem response to
the eruption of Mount St. Helens. Nat Geogr Res 1985, 1:198-216.
69. Steinman AD, Lamberti GA: Lotic algal communities in the Mt. St. Helens
region six years following the eruption. J Phycol 1988, 24:482-489.
70. Kutschera U: Darwin’s philosophical imperative and the Furor
Theologicus.Evo Edu Outreach 2009, 2:688-694.
71. Reif W-E, Junker T, Hoßfeld U: The synthetic theory evolution: general
problems and the German contribution to the synthesis. Theory Biosci
2000, 119:41-91.
72. Scheiner SM: Toward a conceptual framework for biology. Quart Rev Biol
2010, 85:293-318.
73. Niklas KJ: The Evolutionary Biology of Plants Chicago: The University of
Chicago Press; 1997.
74. Kutschera U: From Darwinism to evolutionary biology. Science 2008,
321:1157-1158.
75. Weiner J: Planet Earth New York: Bantam Books; 1986.
76. O’Malley MA: What did Darwin say about microbes, and how did
microbiology respond? Trends Microbiol 2009, 17:341-347.
77. Müller-Wille S: The dark side of evolution: Caprice, deceit, redundancy.
Hist Phil Life Sci 2009, 31:183-199.
78. Schopf WJ: Fossil evidence of Archaean life. Phil Trans R Soc B 2006,
361:869-885.
79. Doolittle WF, Zhaxybayeva O: On the origin of prokaryotic species.
Genome Res 2009, 19:744-756.
80. Cracraft J, Donoghue MJ: Assembling the Tree of Life Oxford: Oxford
University Press; 2004.
81. Kutschera U: Lay aside the ladder of descent. Nature 2011, 471:37.
82. Herrada EA, Tessone CJ, Klemm K, Eguiluz M, Hernandez-Garcia E,
Duarte CM: Universal scaling in the branching of the tree of life. PLoS
One 2008, 3:e 2757.
83. Eldredge N: Macroevolutionary dynamics:Species, niches and adaptive
peaks. New York: McGraw - Hill; 1989.
84. Levin HL: The Earth through Time. 7 edition. Hoboken, John Wiley; 2003.
85. Gradstein FM, Ogg JG, Smith AG, (eds): A geologic time scale 2004
Cambridge University Press, Cambridge; 2004.
86. Szathmary E, Maynard Smith J: The Major Transitions in Evolution Oxford:
Oxford University Press; 1998.
Kutschera Biology Direct 2011, 6:33
http://www.biology-direct.com/content/6/1/33
Page 20