Extinction Rates and Phylogenetic Patterns

Core Idea

Extinction rates vary over geological time and across lineages. Mass extinctions alter ecosystem composition and create radiative opportunities. Modern extinction rates exceed background rates by orders of magnitude, driven by habitat loss, climate change, and invasive species.

Explainer

From your understanding of extinction and recovery dynamics and molecular phylogenetics, you know that species go extinct, that life has rebounded from catastrophic losses, and that evolutionary relationships can be reconstructed from molecular data. Extinction rates and phylogenetic patterns bring these ideas together by asking: how fast do lineages disappear, which lineages are most vulnerable, and what does the tree of life look like after major extinction events?

The background extinction rate is the steady, low-level pace at which species disappear during normal geological time — roughly 0.1 to 1 species per million species-years for most well-studied groups. This baseline allows individual species turnover without disrupting ecosystem structure. Against this background, Earth has experienced five recognized mass extinctions — events where extinction rates spiked to tens or hundreds of times the background rate, eliminating 50–95% of species in geologically brief intervals. The end-Permian extinction (~252 million years ago) wiped out an estimated 90% of marine species; the end-Cretaceous (~66 million years ago) famously eliminated non-avian dinosaurs. Each mass extinction reshaped the phylogenetic tree by pruning entire clades, not just individual species.

Extinction is not phylogenetically random. Some lineages are consistently more vulnerable than others, and phylogenetic analysis reveals why. Species with small geographic ranges, low population sizes, slow reproduction, specialized diets, or large body sizes tend to face higher extinction risk — and these traits are often phylogenetically conserved, meaning closely related species share them. The result is that extinction tends to cluster on the tree of life, removing entire branches rather than plucking random leaves. When a mass extinction eliminates a major clade, it opens ecological space that surviving lineages can radiate into — the explosive diversification of mammals after the dinosaur extinction is the most familiar example. These adaptive radiations fill vacated niches and reshape biodiversity for millions of years.

Modern extinction rates are estimated at 100 to 1,000 times the background rate, driven primarily by habitat destruction, climate change, overexploitation, and invasive species. This has led some biologists to propose that we are entering a sixth mass extinction. Phylogenetic approaches are critical for assessing this claim: by mapping threat status onto evolutionary trees, conservation biologists can identify not just how many species are at risk, but how much unique evolutionary history would be lost. Losing the last species in an ancient, species-poor lineage (like the tuatara or the coelacanth) eliminates far more evolutionary heritage than losing one species from a large, recently diversified clade. This phylogenetic perspective now informs conservation prioritization, helping allocate limited resources to preserve the greatest breadth of the tree of life.