Evolution depends on a simple but essential fact: organisms can pass biological information from one generation to the next. That transmission is called heredity.
If every organism’s traits disappeared when it reproduced, natural selection would have little lasting effect. A useful characteristic that helped one organism survive or reproduce would not reliably appear in its descendants. Likewise, a harmful characteristic would not necessarily decline over generations. Heredity gives evolutionary change a way to persist.
Evolution therefore depends on the interaction of three things: variation among individuals, differences in survival or reproduction, and inheritance of some of that variation. Heredity is the link that connects differences between parents and offspring to changes in populations over many generations.
What heredity means in evolution
Heredity is the passing of biological characteristics from parents to offspring. In organisms that reproduce sexually, offspring receive genetic material from both parents. In organisms that reproduce asexually, descendants generally inherit their genetic material from a single parent.
The inherited information is encoded primarily in DNA, a molecule whose sequence contains instructions used in building and maintaining an organism. Segments of DNA called genes contribute to particular biological characteristics, although most traits are influenced by many genes as well as by environmental conditions.
Heredity does not mean that offspring are exact copies of their parents. Instead, offspring inherit genetic information while also acquiring new combinations of that information and, ultimately, new genetic variants. This combination of continuity and variation is what makes evolutionary change possible.
Why inheritance is necessary for natural selection
Natural selection acts on differences among individuals, but its evolutionary effects occur in populations across generations.
Imagine a population of insects in which some individuals happen to have a genetic variant that makes them better camouflaged against predators. If the better-camouflaged insects tend to survive and reproduce more successfully, they may leave more offspring. If the camouflage trait is heritable, their offspring are more likely to possess genetic variants contributing to that trait.
Over many generations, the variants associated with better camouflage can become more common in the population.
The important point is that selection does not create the useful trait because the organisms need it. Instead, naturally occurring genetic variation already exists, and differences in reproductive success can change how common those variants become. Heredity allows those changes in genetic composition to accumulate.
Without inheritance, selection could favor an individual during its lifetime without producing a corresponding, persistent change in the population.
Genes provide the mechanism of inheritance
The modern understanding of heredity rests on genetics. DNA is organized into chromosomes, and genes occupy specific locations on those chromosomes.
Different versions of a gene are called alleles. For example, a population may contain multiple alleles of a gene involved in a particular biological process. Individuals can inherit different combinations of alleles from their parents.
During reproduction, genetic material is copied and transmitted to offspring. In sexual reproduction, processes such as meiosis and the joining of reproductive cells create new combinations of parental genetic material. As a result, siblings can inherit different genetic combinations even though they have the same parents.
This matters for evolution because natural selection can change the frequencies of alleles in a population. If an allele contributes to a heritable characteristic that increases reproductive success in a particular environment, selection can cause that allele to become more common over generations.
Heredity preserves information, but it is not perfectly faithful
For evolution to occur, heredity needs to provide substantial continuity between generations. At the same time, inheritance must allow occasional differences to arise.
One major source of new genetic variation is mutation, a change in DNA sequence. Mutations can arise from errors during DNA replication or from other biological processes. Most mutations are neutral with respect to reproductive success, some are harmful, and some can be beneficial in particular environments.
Sexual reproduction also reshuffles existing genetic variation. During the formation of reproductive cells, chromosomes are separated and genetic material can be recombined. Fertilization then brings genetic material from two parents together.
These processes mean that heredity is not simply a photocopying system. It preserves genetic information while allowing variation to appear and existing variants to be rearranged.
That balance is crucial. If genetic information were transmitted with no variation at all, populations could not acquire new inherited characteristics. If inheritance were so inaccurate that offspring bore little genetic resemblance to their parents, useful adaptations would be difficult to maintain.
Not every inherited trait is equally visible
A heritable trait is not necessarily controlled by a single gene, and genes do not always determine a trait on their own.
Many characteristics are polygenic, meaning that they are influenced by many genes. Height in humans, for example, reflects the effects of many genetic variants as well as environmental influences such as nutrition and health during development.
Other traits are strongly affected by environmental conditions. A plant may inherit genetic potential for a certain range of growth, but its actual size can depend heavily on water, nutrients, temperature, light, and other conditions.
For evolutionary purposes, what matters is whether differences associated with a trait have a genetic component that can be transmitted across generations. Natural selection can change the frequency of heritable variants even when the visible trait is influenced by both genes and environment.
Heredity and adaptation are closely connected
An adaptation is an inherited characteristic that has been shaped by natural selection and contributes to reproductive success in a particular environment.
Consider a population living where a particular food source is abundant. If individuals with inherited characteristics that help them exploit that food tend to leave more descendants, the genetic variants associated with those characteristics may increase in frequency.
The environment matters because the effect of a genetic variant depends on circumstances. A characteristic that is advantageous in one environment may provide little benefit—or even impose a disadvantage—in another.
This is why evolution does not produce organisms that are universally or permanently “better.” Natural selection changes populations in relation to their environments and reproductive conditions.
Heredity explains why populations, not individuals, evolve
An individual organism develops and lives with a particular genetic makeup. It does not ordinarily evolve genetically during its lifetime in the sense used by evolutionary biology.
Evolution is a change in the inherited characteristics of a population across generations.
Suppose a population initially contains several alleles of a gene. If individuals carrying one allele consistently contribute more offspring to later generations, that allele may become more common. The genetic composition of the population has changed.
Heredity makes this possible because offspring tend to resemble their parents genetically. The reproductive success of one generation can therefore influence the genetic makeup of subsequent generations.
Heredity also allows evolutionary changes to accumulate
Evolutionary change does not have to arise from a single dramatic genetic event. Small inherited differences can be preserved and combined over many generations.
A mutation that has little effect by itself may eventually occur alongside other variants. Natural selection, genetic drift, mutation, migration, and other evolutionary processes can alter the frequencies and combinations of genetic variants within populations.
Over long periods, accumulated genetic differences can produce substantial changes. Populations can become increasingly different from one another, and, under the right conditions, those differences can contribute to the formation of new species.
The underlying principle remains the same: changes can persist because biological information is inherited.
Heredity is broader than DNA, but DNA is central to modern evolutionary biology
In most discussions of evolution, heredity is understood primarily through genetic inheritance. DNA provides the principal mechanism by which information is transmitted from parent to offspring across generations.
There are also biological effects that can influence offspring without being simple changes in DNA sequence. Epigenetic inheritance, for example, involves molecular modifications that can affect how genes are regulated and, in some circumstances, can persist across generations.
These mechanisms do not replace genetic inheritance as the central foundation of evolutionary biology. Rather, they add detail to our understanding of how inherited biological differences can arise and persist.
The essential connection
Heredity makes evolution possible because it gives biological variation continuity across generations.
Mutation and genetic recombination help produce variation. Natural selection can favor some heritable variants over others, while other processes such as genetic drift can change variant frequencies through chance. But none of these processes could produce cumulative evolutionary change without some mechanism for transmitting biological information from one generation to the next.
In that sense, heredity provides the bridge between individual differences and population change. What is inherited can persist; what persists can change in frequency; and changes in inherited variation accumulated over generations are the substance of evolution.
