population, but it does produce new combinations of genes (Ridley,
2004). Gene mixing also occurs during crossing over in meiosis, prior
to sexual reproduction (Futuyma & Kirkpatrick, 2017).
Gene flow12 is the change in gene frequency in a population
resulting from new genes introduced by the arrival of individuals
from other populations (Templeton, 2006).
Nongenetic inheritance13 comprises changes in genetic informa-
tion that do not involve alteration of the DNA (or RNA) sequence of
a genome. At least three mechanisms contribute to nongenetic inher-
itance: (1) epigenetic inheritance, such as the DNA methylation that
often reduces or eliminates gene transcription (Zenk et al., 2017);
(2) parental effects that occur when the genotype or phenotype of
the parents directly influences the phenotype of their offspring;
and (3) cultural inheritance that is transmitted by behavior and
learning (Jablonka & Raz, 2009; Futuyma & Kirkpatrick, 2017).
Phenotypic plasticity14 is the capacity of a genotype (the set of
genes possessed by an individual organism) to generate any of
several phenotypes (the characteristics of an organism produced
by the interaction of its genes with the environment) depending
on the environment. Some evolutionary biologists hold that phe-
notypic plasticity can precede genetic changes (West-Eberhard,
2003; Laland et al., 2015).
These five basic processes generate heritable variation, which in
turn is subject to processes that may change the frequencies of genes
and phenotypes in populations. These processes include genetic
drift and natural selection.
Figure 3. Part of the concept map showing the reconstruction of the history of life.
