The Percentage of Species Surviving to Present Day

Estimates suggest that around 1 to 4 billion species have existed on Earth over its history. Currently, approximately 8.7 million species are estimated to be living, though only around 1.2 million have been formally described by scientists. This raises the natural question: approximately what percentage of the species that have ever existed are on Earth today?

Understanding the Current Estimate

Most estimates suggest that about 0.1 to 0.01 percent of the species that have ever existed are not yet extinct. However, this question is complex and contentious for several reasons.

The Problems with the Question

1. Lack of Knowledge on Current Species

There was a time when it was believed that there were about one million species alive on Earth today. More recent estimates have pushed that number to 3 million, 15 million, or even 30 million. We simply don't know the exact number because new species are discovered annually. This ongoing discovery makes it challenging to provide a precise answer to the percentage of surviving species.

2. The Evolution of Species Definitions

The challenges don't end with just discovering new species. The way we define "species" has evolved over time. Now, species are defined by the ability to produce fertile offspring. However, fossils do not reproduce, leading to a different system of categorization. Therefore, the species we find in the fossil record are defined by morphology alone, which doesn't align with modern definitions of species.

Historical Perspective on Species Extinction

1. Mass Extinctions

While some argue that species survived mass extinctions, the reality is that only unicellular organisms survived major extinction events, whereas multicellular organisms perished in significant numbers. There have been approximately five major mass extinctions over the past 450 million years, each causing a significant drop in biodiversity.

2. Calculating Survival Rates

Roughly a quarter of the species survived each major extinction. This means that after each of the five major extinctions, the remaining species might have been as low as 1 in 1,024. If we consider mutations and the replacement by better adapted species, the survival rate could be even lower. For example, none of the hominins that evolved over the past 6 million years have survived, and the same applies to many other species.

3. Examples of Persistent Species

There are exceptions, such as sharks, which have survived for about 450 million years, cockroaches for 300 million years, and coelacanths for 65 million years. However, these are rare exceptions. The vast majority of species, if not all, have gone extinct.

Conclusion

Given the vast numbers of species that have existed on Earth and the significant periods during which they were alive, it is probable that less than one percent of the species that ever lived on Earth are still alive today. The complexity of the question and the limitations of our current knowledge make it impossible to provide a definitive answer. Nonetheless, it is clear that the vast majority of species that have ever existed are now extinct.