The 4 billion year story of life is written in our DNA

Science · Published 23 October 2026 Swipe more like this →

In short: Evolution is not just a historical event, but a continuous process of change in heritable characteristics. From the microscopic bacteria of the ancient past to the complex biodiversity of today, understanding how populations shift through mutation and selection reveals the profound interconnectedness of all living things.

At its core, biological evolution is the change in heritable characteristics of populations over successive generations. This process is driven by several key mechanisms: natural selection, where individuals with advantageous traits are more likely to survive and reproduce; genetic drift, which involves random changes in gene frequencies; mutations, which introduce new genetic variations; and gene flow, the movement of genes between populations. While Charles Darwin and Alfred Russel Wallace independently conceived the theory of natural selection in the mid-19th century, it was not until the early 20th century that modern evolutionary theory emerged by synthesizing these ideas with Mendelian inheritance and population genetics.

The evidence for this descent with modification is found across multiple scientific disciplines. The fossil record provides a chronological progression, moving from early biogenic graphite to microbial mats and eventually fossilized multicellular organisms. We also see evidence in homologies—structural or genetic similarities between species—and in biogeography. Modern molecular biology, which advanced significantly since the 1960s, allows scientists to compare genetic sequences directly. For instance, we now know that humans and chimpanzees differ by only about 1–2 percent in their genetic units.

This evolutionary lineage traces back to a Last Universal Common Ancestor (LUCA) that lived approximately 3.5 to 3.8 billion years ago. All life on Earth shares this common origin. Over eons, this single lineage branched into the staggering diversity we see today, including over 2 million named species. This history includes the rise of archosaurs, such as dinosaurs and birds, which have dominated ecosystems for over 250 million years, and the divergence of mammals from shrewlike creatures more than 150 million years ago.

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