Why can't evolution work on traits that aren't inherited?
Evolution is a change in what is inherited across generations. Natural selection shapes heritable traits in ways that affect fitness, and genetic drift changes the frequency of inherited variants, especially in small populations [4]. Both processes require that the trait in question be passed from one generation to the next. A trait that is not inherited—say, a scar or a skill learned in one lifetime—cannot be passed on, so it cannot become more or less common in a population over time.
The origin of DNA-encoded heritable traits is itself treated as a key step in the emergence of Darwinian evolution. In models of early life, the transition to a world where DNA sequences encode heritable phenotypes is what allows populations to evolve by natural selection [3]. This suggests that heritability is not just a detail of evolution but a precondition for it: without a mechanism to pass traits to offspring, there is no lasting variation for selection to act on.
What does it look like when evolution acts on heritable traits?
In fisheries, harvesting can cause genetic changes in heritable traits of targeted fish stocks. Size-selective fishing typically selects for younger and smaller spawners, which is the opposite of what natural selection would favor [5]. This is a clear example of evolution in action: because the traits are heritable, the selective pressure from fishing changes the genetic makeup of the population, with potential knock-on effects through the food web [5].
In plant disease systems, natural selection shapes heritable traits in ways that maximize host fitness, and coevolution between hosts and pathogens involves reciprocal selection on inherited traits [4]. The traits that influence these interactions are often evolutionarily conserved, meaning they are inherited and can be traced through lineages [4]. This shows that heritability is what allows traits to respond to selection over many generations, whether the selector is a predator, a pathogen, or a human harvester.
Why do heritable differences within a species matter for evolution?
Not all heritable differences are simply genetic noise. A 2025 analysis of quantitative traits asks whether heritable individual differences are adaptive or non-adaptive, and distinguishes several different questions about their evolution [1]. The key point is that heritable variation is the substrate on which selection and drift can act. Without heritable differences among individuals, a population cannot evolve in response to selection, because there is nothing for selection to favor or disfavor.
In plants, reproductive traits such as flower number and inflorescence branching are heritable and have evolved in diverse ways across the Cyperaceae family. Comparative analyses show that these traits can be reconstructed through evolutionary history and that some traits are correlated with each other [2]. This illustrates that heritable traits are the ones that leave a trace across generations—the ones that can be studied as evolving characters.
Sources used in this answer
Are heritable individual differences just genetic noise? What the architecture of quantitative traits says about their evolution
Heritable individual differences can be adaptive or non-adaptive, and their evolution depends on genetic architecture and selection processes.
Inherit the wind: evolution of reproductive traits in Cyperaceae
Reproductive traits in Cyperaceae are heritable and have evolved in diverse ways, with some traits correlated across the family.
The RNA-DNA world and the emergence of DNA-encoded heritable traits
The emergence of DNA-encoded heritable traits was a key step in the transition to Darwinian evolution, where DNA sequences encode heritable phenotypes.
Evolution
Natural selection shapes heritable traits to influence fitness, and genetic drift changes allele frequencies, both requiring heritable variation.
Marine food web perspective to fisheries‐induced evolution
Fisheries-induced evolution changes heritable traits in targeted fish stocks, often selecting for younger and smaller spawners.