Answer
When we say biology is both vertical and horizontal, we mean the hierarchical organization of life as well as the diversity therein. The vertical scale of biology begins with the biosphere, and then descends into levels of the ecosystem, communities, populations, organisms, organ systems, organs, tissues, cells, and organelles. Meanwhile, the horizontal scale considers diversity of life and across a long time scale. The horizontal scale considers the different domains, kingdoms, phyla, classes, orders, families, and species and how so many different, diverse ones exist at the same time.
Work Step by Step
Biologists explore life in both vertical and horizontal dimensions. The subfield of taxonomy is especially important in this context as this field classifies life both vertically and horizontally.