Genetic drift15 is represented by random, nonadaptive changes
in the frequency of two or more genotypes within a single population because of fluctuations due to “errors of sampling” (random
processes; Graur & Li, 2000). An example is the so-called “
bottleneck” process (Templeton, 2006; Futuyma & Kirkpatrick, 2017),
whereby a small number of individuals from a population migrate
and establish themselves as settlers (founders) of a new population.
Because the founders represent only a small sample of the original
population, the frequencies of genotypes in the new population
may differ by chance from those of the source population.
Natural selection16 reflects the fact that different phenotypes have
different survival and/or reproduction capacity in the environment in
which they are expressed. Differential survival generates differential
perpetuation of the respective genotypes. Adaptation to that characteristic increases the survival and/or reproduction of the organism that
carries it, in a determined environment. Natural selection is the only
known mechanism that generates adaptations by acting on naturally
occurring variation, so one might say that an adaptation is a feature
that evolved by natural selection (Futuyma & Kirkpatrick, 2017).
Two phenomena could influence natural selection: developmental
processes and niche construction.
Developmental processes17, based on features of the genome that
may be specific to a particular group of organisms, can influence the
range of traits on which natural selection can act (Laland et al., 2015).
Niche construction18 is the process whereby organisms actively
modify their environment and consequently modify their evolutionary niches (Odling-Smee et al., 2003).
Natural selection and genetic drift generate and modify biodiversity. That diversity is not a continuum, because a reduction of the
genetic interchange19 between populations (which usually generates
reproductive isolation) leads to speciation20 and to the formation of
new species (Coyne & Orr, 2004).
The definition of a species21 is very controversial (Crisci, 1981),
and it has been defined in many ways for plants, animals, and
microorganisms (Van Regenmortel, 1997). The most widely used,
but not uncontested, criterion is the biological concept of species:
a group of natural, genetically similar, interfertile populations that
are reproductively isolated from other such groups (Mayr, 1970).
Speciation, therefore, is responsible for the discontinuities we
observe in the diversity of life – that is, the absence of a smooth continuum in life’s history. These discontinuities range from the species
level (microevolution) to higher-ranking taxa (macroevolution)
(Futuyma & Kirkpatrick, 2017). Macroevolutionary changes occur
with the appearance of characteristics that distinguish large groups22,
such as mammals, insects, or flowering plants. They are changes that
occur on a geological timescale (Jablonski, 2007). Macroevolution
includes two schools of thought: gradualism and saltationism.
Gradualism23 proposes that macroevolution results from the
accumulation of small modifications throughout geological periods.
The only difference between macroevolution and microevolution
would then be the amount of time in which they elapse. Macroevolution, in this view, is a simple extension in time of microevolution.
Saltationism24, on the other hand, proposes that macroevolution
includes processes that operate only at macroevolutionary levels. For
example, large changes in chromosomes (macromutations) would
give rise to very different organisms, which would adapt to new ways
of life and generate differences between large groups.
One can resolve the binary distinction between gradualism
and saltationism with the following argument: The evolutionary
forces of microevolution work and are responsible for most of
the large groups we see today. In the long history of life, however,
there have been occasional occurrences of unique events that have
had great consequences (Grant, 1977). An example of the last
type is the evolutionary event by which a symbiotic bacterium
was transformed into mitochondria of the cells of most other living beings (Margulis, 1998).
A special case of evolution is that produced by human
manipulation such as genetic engineering25, also called genetic
modification or genome editing. It is the direct manipulation of
an organism’s genome using biotechnology to produce genetically modified organisms (Vanloqueren & Baret, 2009). To the
extent that those changes are transmitted to subsequent generations, the possibility exists to alter the evolutionary trajectory
of the species in question. That possibility is one of the vexing
challenges inherent in the now pervasive application of CRISPR-based genetic editing (Dickinson & Goldstein, 2016; Winblad &
A concept map of evolutionary biology is a way to promote meaningful learning in biology. In this case, the concept map is an educational tool that generates a context of ideas around every main
concept of the subject in an introductory road map to biological
Biological evolution is a great and stirring account of life on
Earth and of human origins within it. It speaks of our connectedness to the rest of life on Earth and invokes our stewardship of
our planet and its biodiversity. Biological evolution also can be
inspirational by exposing students to the wonders of nature, such
as flowers that attract pollinators by mimicking females, deep-sea
fish that can swallow prey larger than themselves, and snakes that
can strike mammalian prey in darkness by sensing their body heat.
Exposure to evolutionary theory concerns not merely the facts of
natural selection, common ancestry, homology, or speciation, but
also the amazing array of things that organisms do by virtue of their
adapted states (Douglas Futuyma, Stony Brook University, personal
communication, June 6, 2016).
But there is something else important about the study of evolutionary theory: it causes us to engage with one of the most
impressive and far-reaching achievements of the human intellect,
and it is evolution itself that has provided us with the intellectual
capacity to apprehend our own history and our place in the
We acknowledge Douglas Futuyma, Elián Guerrero, and Edgardo
Ortiz-Jaureguizar for their useful comments on a first draft of the
concept map. Those faults that remain are entirely our responsibility. Piero Marchionni and Mary Rose Stoltz provided technical
assistance. The reviewers are also acknowledged for their useful
comments and suggestions.