Key Terminology (Grade 12 NSC Matric Life Sciences): Revision Notes

Key Terminology

Introduction

Understanding evolution by natural selection requires mastery of specific scientific vocabulary. These key terms form the foundation for explaining how species change over time, how new species develop, and what drives evolutionary processes. Each term connects to the bigger picture of how life on Earth has diversified and continues to evolve.

Essential evolutionary terms

Biological evolution

This refers to hereditary genetic changes that occur within groups of organisms across multiple generations. Think of it as the gradual transformation of species over time through inherited modifications. Evolution isn't something that happens to individual organisms during their lifetime, but rather describes changes that accumulate in populations as advantageous traits get passed down from parents to offspring. These genetic alterations become established when they provide survival or reproductive benefits.

Biological species

A biological species consists of organisms that share similar traits and can successfully mate with each other to produce offspring capable of reproduction themselves. This concept emphasises reproductive compatibility rather than just physical appearance. For example, different breeds of dogs can interbreed and produce fertile puppies, making them all part of the same biological species despite looking very different. The key requirement is that the offspring must be fertile and able to reproduce.

Population

A population describes all the individuals belonging to the same species that live together in a specific area or habitat. This is the actual group where evolution takes place, as genetic changes occur within these local communities rather than across entire species globally. For instance, all the springbok living in a particular nature reserve would form a population, separate from springbok populations in other reserves.

Natural selection

This fundamental evolutionary mechanism explains how environmental pressures determine which organisms survive and reproduce successfully. Individuals with characteristics that help them thrive in their specific environment are more likely to live long enough to pass these beneficial traits to their descendants. Over many generations, these advantageous features become more common in the population. Natural selection acts like a philtre, allowing well-adapted organisms to flourish while less suitable individuals struggle to survive.

Artificial selection

Unlike natural selection, this process involves humans deliberately choosing which organisms reproduce based on desired characteristics. Farmers and breeders use artificial selection to develop crops with higher yields, livestock with better meat quality, or pets with specific appearances. The selective pressure comes from human preferences rather than environmental challenges. Examples include breeding cattle for milk production or developing different flower colours in roses.

Breeding patterns

Inbreeding

This occurs when organisms that share close genetic relationships mate with each other. While this can help maintain desired traits within populations, it often leads to reduced genetic diversity and increased risk of harmful genetic conditions appearing in offspring.

Outbreeding

This involves mating between organisms that aren't closely related genetically. Outbreeding typically increases genetic variation within populations and often produces healthier offspring with better survival chances. Many species have natural mechanisms that encourage outbreeding.

Species formation processes

Speciation

This describes the evolutionary process through which new species develop from existing ones. Speciation occurs when populations become so genetically different that they can no longer successfully interbreed to produce fertile offspring. This process typically takes thousands or millions of years.

Geographic speciation

This specific type of speciation happens when physical barriers separate members of the same species into different populations. Mountains, rivers, or islands can isolate groups, preventing gene flow between them. Over time, each separated population evolves independently, potentially becoming distinct species. The Galápagos finches that inspired Darwin's thinking evolved through geographic speciation.

Reproductive isolation

These are biological mechanisms that prevent different species from successfully mating and producing fertile hybrid offspring. Reproductive barriers can include differences in mating behaviours, breeding seasons, or genetic incompatibilities. These mechanisms help maintain species boundaries and prevent the blending of distinct evolutionary lineages.

Punctuated equilibrium

This evolutionary pattern describes how species often remain relatively unchanged for extended periods, followed by brief intervals of rapid evolutionary change. Rather than gradual, constant transformation, evolution sometimes occurs in bursts when environmental pressures suddenly intensify or new ecological opportunities arise.