Yes. Fossil evidence suggests that more species are alive on Earth today than at any previous time, although the exact number of living or past species cannot be determined.
Why Has Species Diversity Increased?
This is part of IB Biology A4.2, Conservation of biodiversity, and is required at both SL and HL. Over geological time, speciation has produced new species by splitting pre-existing species, while extinction has removed species.
The long-term trend has been an increase in global species diversity because lineages have repeatedly diversified and occupied new ecological niches. Evolutionary innovations and events such as adaptive radiations have enabled organisms to exploit different habitats and resources.
However, biodiversity has not increased continuously. Earth has experienced several mass extinction events during which a large proportion of species disappeared over a relatively short geological period. Diversity subsequently recovered as surviving lineages underwent speciation.
Evidence or issue | Significance |
|---|---|
Increasing diversity in the fossil record | Supports the conclusion that more species exist today than in most or all past periods |
Mass extinction events | Show that biodiversity has repeatedly fallen sharply before recovering |
Incomplete fossil record | Prevents exact comparisons because many organisms never fossilized or have not been discovered |
Undiscovered living species | Means the present number of species is also uncertain |
A common misconception is that the current biodiversity crisis means fewer species exist now than at every earlier point in Earth’s history. This is incorrect: present biodiversity may be historically high while the current rate of anthropogenic extinction is also dangerously high. These statements describe different things: total species richness and the rate at which species are being lost.
Exam Technique
For a state question, write: “Fossil evidence suggests that more species are alive today than at any time in the past.” For an evaluate question, add that both fossil and present-day species counts are incomplete, so the conclusion is evidence-based rather than an exact measurement.
