Question

The theory of evolution by natural selection requires variability of a given trait. Why is variability necessary and where does it come from?

Short answer

Variability is crucial for the process of evolution by natural selection as it allows species to adapt to changing environments. It primarily originates from mutations and sexual reproduction, resulting in a variety of traits among individuals in a species.

Step-by-step solution

Understanding Evolution by Natural Selection

Evolution by natural selection refers to the process in which species change over time adapted to their environment. Charles Darwin theorized this as 'survival of the fittest.' Those organisms are more fitted and have advantageous genes are more likely to survive and reproduce, passing their traits to their offspring.

Importance of Variability

Variability is crucial in the natural selection process because it enables populations to adapt to changing environments. Without variation, all organisms of a species would be identical. If the environment changes, the uniformly-expressing traits might not support survival. But with variation, some organisms might possess traits that enable them to adapt and survive, and pass on these favorable traits to the next generation.

Source of Variability

Variability comes from two main sources: mutation and sexual reproduction. Mutation is a change in the DNA sequence of a gene, causing a different characteristic to be expressed. Sexual reproduction, on the other hand, leads to variation because it allows the offspring to inherit a unique combination of genes from both parents.

Key concepts

Variability in Species

Variability within species is indispensable to the mechanisms of evolution. Think of it as nature's vast palette of traits that allow organisms to adapt and thrive. This genetic diversity arises from multiple factors, including gene mutations and the shuffling of alleles during sexual reproduction.

For instance, a population of beetles might exhibit different colors: some green, some brown. This color variation could be due to random mutations, the random assortment of genes from their parents, or a combination of both. If the environment favors brown beetles because they are less visible to predators, over time, the proportion of brown beetles will increase. This is evolution at work, powered by variability in species.

Survival of the Fittest

The phrase 'survival of the fittest', coined by Herbert Spencer and popularized by Charles Darwin, doesn't necessarily mean the strongest or fastest individuals survive. Instead, it refers to organisms that fit best in their environment. It's like a lock and key model, where the organisms with traits that 'unlock' the advantages in their environment are the ones that survive and reproduce.

Imagine a species of birds with varying beak sizes. On an island where the only food source is hard seeds, birds with bigger, stronger beaks are more 'fit' as they can easily access food. Over generations, these birds will predominate, illustrating how survival of the fittest guides evolutionary processes.

Genetic Mutation

Genetic mutations are the random errors that occur during DNA replication. These errors can lead to changes in the genetic code and can result in new traits in an organism. Think of genetic mutations as unintentional experiments by nature, some of which can produce features that give organisms a survival advantage.

For example, a mutation in a flower might result in a new, vibrant petal color. If pollinators prefer this new color, the mutated flower variant will likely have more reproductive success, and the trait will spread through the population. Mutations add to the natural variability upon which natural selection acts.

Sexual Reproduction

Through the magic of sexual reproduction, genetic mixing occurs, leading to offspring that are genetically distinct from their parents. During this process, genes from two parents are combined in unique ways by the random assortment of chromosomes during gamete formation and by crossover events.

Consider how siblings look similar yet distinct due to inheriting different combinations of their parents' genes. This jumbling of genetic materials ensures ample variability among individuals, providing a rich substrate for natural selection to act upon in the continual dance of evolution.

Adaptation to Environment

Adaptations are the traits that increase an organism's chances of survival and reproduction in a particular environment. These traits can range from the physical, like the thick fur of arctic foxes for warmth, to behavioral, like birds migrating to warmer climates during winter.

Adaptive traits emerge over generations as those individuals with characteristics suited to their environment tend to live longer and leave more offspring. Such traits become more common in the population, and this is how species evolve. It's a continuous process of trial and error, with the environment determining which variations work best.