now stored in Cambridge University Library), the image of a family
tree to represent the history of life. The only illustration in On the
Origin of Species (Darwin, 1859) is a hypothetical tree of life.
Life on Earth came from a common ancestor more than 3.5 billion
years ago; it then branched out over time, generating many new and
diverse species reflected in the phylogeny of life (Coyne, 2009). The
history of life has always been influenced by the history of the Earth3.
Fossils (remains or evidence of life >5000 years old) are traces of
that past and are a fundamental element for establishing the minimum
age of groups and the rates of evolution of each (Pascual & Ortiz-Jaureguizar, 2007; Wyse Jackson, 2010). Fossils also reveal the
phenomenon of extinction (disappearance of all members of a group
of living beings), a fact common in the history of life (Lomolino
et al., 2010).
Currently, scientists reconstruct the history of life by using
phylogenetic methods, which are based on the character distribution of organisms and on applying homology4 as evidence of common ancestry. Homologous characters are those that originated,
with or without modification, from the common ancestor of that
group (Hall, 1994). The most widely used techniques of phylogenetic reconstruction5 are parsimony, maximum likelihood, and
Bayesian inference (Felsenstein, 2004; Baum & Smith, 2012).
Phylogenetic trees6 are active hypotheses about order in nature
and, as such, are refined or amended through continued research
(e.g., the finding of new characters). The phylogenetic tree of the
different groups of organisms is assembled to build a hypothesis
about the tree of life (Hillis, 2010).
Furthermore, phylogenetic trees are the basis of classifications7 that have explanatory and predictive power because they
reflect the generative system responsible for the observed attributes of the organism: biological evolution (Crisci et al., 2014).
These classifications provide a reference system for the whole of
biology (Crisci, 2006).
What Processes, in Mutual Influence with the
Interaction among Organisms and Their
Environment, Generated the History of Life?
The first step in answering this third question is to investigate the
mechanisms of evolution (Figure 4).
The mechanisms at the population level8 are subject to the interaction of organisms with their environment9 (Pianka, 2011). These
processes generate genetic change and are due mainly to three
well-settled mechanisms – mutation, genetic recombination, and
gene flow (Futuyma & Kirkpatrick, 2017); and two mechanisms
whose importance is still a matter of debate – nongenetic inheritance
and phenotypic plasticity.
Mutation10 is the alteration of a gene whether or not it generates
a change in the characteristics of the organism (Hamilton, 2009).
Genetic recombination11 shuffles the genes of both parents during
sexual reproduction. It does not change the frequency of genes in the
Figure 2. Concept map of evolutionary biology showing the two components of evolution: history of life and processes that