Genes, inheritance and selection Study Guide

Evolution by natural selection describes how species change over many generations. The process starts with variation within a population of organisms. Individuals in any population display some differences in their characteristics, known as phenotypes. This variation arises partly from random mutations in DNA, which can be passed on to offspring. If environmental conditions change or resources become scarce, there will be competition for survival. Individuals with phenotypes that make them better suited to their environment are more likely to survive and reproduce. For example, an animal with better camouflage might be more successful at avoiding predators, or a plant with deeper roots might be better at finding water during a drought. These 'fitter' individuals pass on their advantageous genetic traits to their offspring. Over time, as generations continue, these favourable traits become more common in the population because more individuals possessing them survive and successfully reproduce. Conversely, individuals with less favourable traits are less likely to survive and pass on their genes. This continuous process, acting over vast periods, leads to gradual changes in the characteristics of a population, eventually resulting in the evolution of new species or better-adapted forms of existing ones. This mechanism is often summarised as 'survival of the fittest'.

Genetic variation refers to the differences in the inheritable characteristics, or genes, within individuals of a population. This means that not all individuals of the same species are identical; they have slightly different traits due to variations in their genetic makeup. For example, within a population of humans, some individuals might have blue eyes, while others have brown eyes. Some might be tall, others short. These differences are a result of genetic variation. This variation is crucial for the survival of a species. If all individuals were genetically identical, a single change in the environment, like a new disease or a shift in climate, could wipe out the entire population because no individuals would have the necessary traits to survive. However, with genetic variation, some individuals might possess traits that make them more resistant to the disease or better adapted to the new climate, allowing them to survive and reproduce. This process, where individuals with favourable variations are more likely to survive and pass on their genes, is a fundamental concept in natural selection and evolution. The sources of this variation include mutations, which are random changes in DNA, and sexual reproduction, which combines genetic material from two parents in a new way.