Life Defined
All living things share certain basic characteristics. They grow, feed, respire, and reproduce—either sexually or asexually. They also produce waste or by-products, and these often support other life. For example, bacteria break down organic matter, releasing nutrients that plants can absorb. In turn, plants produce oxygen during photosynthesis, which we and countless other creatures breathe. Life is interconnected in this way, a delicate web that has been evolving for billions of years.
Some characteristics, like movement and senses, are more complex. Plants, for instance, can sense and grow toward light, but they cannot move from place to place. Viruses blur the lines further—they rely on hosts to reproduce, so whether they are truly “alive” remains a topic of debate.
Understanding these patterns through evolutionary ecology helps us appreciate the richness and fragility of life today. The biodiversity we see in our gardens, forests, and wetlands is a snapshot of the Holocene epoch, a brief moment in Earth’s long history. Past eras, stretching back billions of years, have seen life evolve, diversify, and go extinct. Future epochs will continue this cycle, producing new adaptations and, inevitably, new extinctions.
Even in our own gardens, we can witness the results of co-evolution—species shaping each other over millions of years. Flowering plants and insects, for example, have developed mutually beneficial relationships over the past 140 million years. Flowers provide nectar, and insects pollinate the plants in return. About 35 million years later, wind-pollinated grasses evolved, offering a different but highly efficient way for plants to reproduce. Evolution works in many ways, and history shows that some species survive while others vanish, just as trilobites, ammonites, and dinosaurs are now gone.
Today, humans are shaping the planet faster and more profoundly than any species before us. Scientists generally agree there have been five major mass extinctions in Earth’s past—and many now believe we are in the midst of a sixth, driven by human activity. Some call this the Holocene or Anthropocene extinction. Whether immediate or gradual, the impact of our actions on biodiversity is undeniable.
Our global population now exceeds eight billion, and while individual actions may seem small, collectively they matter. Choosing to protect habitats, plant native species, and nurture wildlife can help guide the future of life on Earth in a more balanced way. Every garden, pond, or green space contributes to a healthier, more resilient ecosystem.
Some of life’s earliest survivors, such as bacteria, archaea, and viruses, have remained remarkably unchanged for around 4 billion years. Blue-green algae (cyanobacteria) still form mats on ponds, lichens and mosses cling to rocks, and ancient plant lineages like ferns, cycads, and conifers remind us of the greenery that once shaded dinosaurs. Grasses, a much more recent addition, evolved only around 20 million years ago, but today they dominate many landscapes.
Even a simple rock surface covered in lichens, mosses, grasses, and woody plants tells the story of life colonizing land over 500 million years ago. By observing these small details in our gardens and local wild spaces, we glimpse the slow but extraordinary march of evolution—and the remarkable resilience of life when it is allowed to thrive.