The lowest category in a taxonomical hierarchy is the species. Taxonomy is the science of classifying and naming organisms based on their characteristics and evolutionary relationships. It provides a system for organizing and categorizing the vast diversity of living organisms on Earth.

1. Taxonomical Hierarchy:
Taxonomy follows a hierarchical system with various levels or categories. These categories, from highest to lowest, are:

- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species

Each level represents a progressively more specific grouping of organisms. The lowest level, species, represents the most specific category in the taxonomical hierarchy.

2. Species Definition:
A species is defined as a group of organisms that can interbreed and produce fertile offspring. Members of the same species share common characteristics and can freely exchange genetic material. They are reproductively isolated from other species, which means they cannot interbreed with organisms from different species.

3. Importance of Species:
Species is a fundamental unit of classification because it represents the basic building block of biodiversity. The diversity of species on Earth is immense, and each species plays a unique role in maintaining ecological balance and functioning of ecosystems. Understanding and identifying different species is crucial for conservation efforts, ecological research, and understanding evolutionary relationships.

4. Species Naming:
Each species is assigned a unique scientific name consisting of two parts: genus and species epithet. This naming system is known as binomial nomenclature, introduced by Carl Linnaeus in the 18th century. The genus represents a broader group of closely related species, while the species epithet distinguishes one species from another within the genus.

5. Example:
For example, humans belong to the species Homo sapiens. Here, Homo represents the genus, and sapiens represents the species epithet. This scientific naming system ensures clear and precise identification of organisms across different languages and regions.

In conclusion, the lowest category in the taxonomical hierarchy is species. Species represents the most specific grouping of organisms and is defined by their ability to interbreed and produce fertile offspring. Understanding and classifying species is crucial for studying biodiversity, conservation, and understanding the intricate relationships between different organisms.