Natural selection is a fundamental mechanism of evolution that occurs in populations over time. Individuals with certain traits are more likely to survive, reproduce, and pass on their genes to future generations, thereby influencing the genetic makeup of the population. This process results in the adaptation of populations to their specific ecological niches and the emergence of new species over a period of time. It is a gradual and ongoing process that has shaped the diversity of life on Earth.
Natural Selection
The term natural selection was proposed by Charles Darwin. The basic concept of natural selection is as follows: within a population, individuals exhibit variation in their traits, such as their physical characteristics. Some of these traits may be advantageous, making individuals better adapted to their environment and increasing their chances of survival and reproductive success. Other traits may be disadvantageous and reduce an individual’s fitness. Individuals with advantageous traits pass on these traits to their offspring, increasing the frequency of those traits in the population. Over time, the population becomes better adapted to its environment as the advantageous traits become more prevalent. Natural selection is driven by several key factors such as:
- Genetic and phenotypic variation within a population, which can be inherited and passed on to future generations.
- Selective pressure imposed by the environment influences the characteristics and traits of an individual.
- Through inheritance, the traits that confer advantages are passed on to offspring.
- Differential reproduction means individuals with traits that confer advantages are more likely to survive, reproduce, and pass on their genes to the next generation.
History
Before Charles Darwin, there were some early theories that gave an idea about the concept of natural selection. However, these theories lacked the comprehensive explanation and evidence-based support that Darwin’s theory provided. A few of the theories are explained as follows:
- Lamarck suggested that organisms could change and acquire new traits during their lifetime in response to their environment. He further proposed that these acquired traits could be passed on to offspring, leading to species transformation over time. However, Lamarck’s theory lacked a mechanism for how traits were inherited accurately, and it did not account for the role of variation and competition in natural selection.
- Charles Darwin’s grandfather, Erasmus Darwin, proposed ideas about the transmutation of species and the concept of common descent. Erasmus Darwin’s ideas influenced Charles Darwin’s later work, but he did not provide a detailed mechanism for natural selection.
- Thomas Malthus, an economist, proposed the idea that populations tend to grow exponentially while resources remain limited, leading to competition and a struggle for survival. This concept influenced Darwin in developing his theory of natural selection.
Darwin’s theory of Natural Selection
Charles Darwin’s theory of evolution by natural selection, presented in his book “On the Origin of Species’‘ proposed that species change and adapt over time through a process driven by two key factors: variation and natural selection. Within a population, individuals exhibit variations in their traits, which can arise from genetic mutations or be inherited from their parents. These variations influence the ability of individuals to survive and reproduce in their environment, leading to a struggle for existence. Individuals with traits that provide advantages in this struggle, such as better camouflage or more efficient foraging, are more likely to survive and pass on their advantageous traits to their offspring. Over successive generations, as advantageous traits become more common, populations become better adapted to their environment, giving the concept of ‘‘survival of the fittest”. This gradual accumulation of small changes can lead to the emergence of new species and the diversity of life we observe today.
How does Natural Selection work?
Natural selection is a key factor in evolution and works through various interconnected steps. The steps are :
- First, within a population, there exists variation, meaning individuals exhibit different traits. These variations can be inherited or arise from genetic mutations.
- Second, the environment exerts selective pressures on individuals. These pressures can be biotic, such as competition for resources or predation, or abiotic, including climate or habitat conditions. Certain traits may provide advantages in dealing with these pressures.
- Third, there is differential survival and reproduction. Individuals with advantageous traits are more likely to survive and reproduce, passing on their genes to the next generation. This leads to a greater representation of those advantageous traits in subsequent populations.
- Fourth, the process of heredity ensures that the advantageous traits are inherited by offspring, increasing their prevalence in the population over time.
- Finally, this process leads to the accumulation of beneficial traits in the population, enhancing the overall fitness and adaptation of the species to its environment. Gradually, populations become better suited to their specific ecological niches. This ongoing process of natural selection continuously shapes the characteristics and diversity of life on Earth.
Examples of Natural Selection
There are numerous examples of natural selection observed in nature that show how this mechanism shapes the traits and characteristics of different species. Here are a few examples:
- Peppered Moths (Biston betularia): During the industrial revolution in England, the population of light-colored peppered moths underwent natural selection. Light-colored peppered moths mutated to dark color, as industrial pollution darkened the tree trunks, a mutation causing dark-colored wings to become advantageous. The dark-colored moths had better camouflage against the sooty background, leading to their increased survival and reproduction. Over time, the proportion of dark-colored moths in the population rose significantly.
- Darwin’s Finches: Darwin noticed diverse finches on the Galapagos Islands, each with a beak tailored to its diet. For example, finches with robust beaks cracked nuts, while those with slender beaks fed on insects. Different food sources created selective pressures, favoring finches with efficient beak shapes. This led to diverse beak forms among finch species.
- Antibiotic Resistance in Bacteria: Bacteria can evolve resistance to antibiotics through natural selection. When exposed to antibiotics, most bacteria are killed, but a few may carry genetic mutations that make them resistant. These resistant bacteria have a survival advantage and can reproduce, passing on their resistance traits to offspring. With continued antibiotic use, the population of resistant bacteria increases, rendering the antibiotic less effective over time.
- Mimicry in Butterflies: Some butterfly species exhibit mimicry, where they have evolved to resemble toxic or unpalatable species. This adaptation provides protection from predators. Individuals with a closer resemblance to the toxic species have a higher chance of survival, leading to the selection of the mimetic traits in the population.
Are we still Evolving?
Evolution is an ongoing process that occurs over long periods of time, and it continues to shape the genetic makeup of populations, including our own. While the timescale of human evolution is much slower compared to other organisms, factors such as natural selection, genetic drift, mutation, and gene flow still influence the genetic diversity and characteristics of human populations.
FAQs on Natural Selection
Q: What is natural selection?
Answer:
Natural selection is the process by which certain traits or characteristics become more or less common in a population over time due to their impact on an organism’s survival and reproduction in a particular environment.
Q: Who proposed the concept of natural selection?
Answer:
The concept of natural selection was proposed by Charles Darwin and Alfred Russel Wallace in the mid-19th century as a key mechanism driving the evolution of species.
Q: Can natural selection lead to the extinction of species?
Answer:
Yes, natural selection can lead to the extinction of species. If a species fails to adapt to changing environmental conditions or faces intense competition from other species, individuals with less favourable traits may have reduced survival and reproductive success. Over time, this can lead to the decline and eventual extinction of the species.