Living Fossils Are Dead! Long Live Living Fossils

Summary

This SciShow episode explores the concept of 'living fossils,' a term coined by Charles Darwin to describe species that have changed little over millions of years. While many such organisms, like crocodiles and horseshoe crabs, appear unchanged, genetic research reveals they have evolved significantly. Scientists now argue for redefining the term to identify ancient lineages, which could help in biodiversity conservation. The video also discusses modern efforts, such as the Evolutionary Performance Index and the concept of 'Endangered Living Fossils,' to standardize and protect these unique species.

Takeaways

• 🦖 Darwin coined the term 'living fossils' for organisms that seem unchanged over time, but it's now a contentious term.
• 🧬 Genetic research shows that organisms like crocodiles and horseshoe crabs, despite looking ancient, have undergone significant genetic changes.
• 🔬 Evolution happens continuously in all species, and visible traits do not always reflect evolutionary change.
• 📊 A new 'Evolutionary Performance Index' (EPI) was developed to better classify living fossils using factors like age, species diversification, and evolutionary branch age.
• 🦈 Some species like sharks, once considered living fossils, don’t meet modern standards due to significant changes over time.
• 🌳 The ginkgo tree, an ancient lineage survivor, exemplifies the concept of a modern species that has evolved genetically but retains ancient physical traits.
• 🌍 A Spanish research team proposed a new term, 'Endangered Living Fossils' (ELFs), focusing on species at risk of extinction that come from ancient lineages.
• 🐠 Coelacanths, thought to be extinct until discovered in 1938, are a prime example of an endangered living fossil with ancient lineage ties.
• 🧪 The goal of these new classifications is not to imply that species haven't changed, but to highlight their evolutionary significance and need for conservation.
• 📚 Scientists are working to standardize these terms to improve biodiversity research and protect ancient species.

Q & A

What did Charles Darwin mean by 'living fossils'?

Charles Darwin used the term 'living fossils' to describe organisms that appeared to have changed very little over millions of years, such as crocodiles and horseshoe crabs. He believed these organisms could offer a glimpse into the past.

Why is the concept of 'living fossils' considered contentious today?

The concept is contentious because modern genetic research has shown that, despite looking similar to their ancient ancestors, organisms like horseshoe crabs and crocodiles have undergone significant genetic changes over time. The term 'living fossil' suggests stasis, but evolution affects all species, even if physical appearances don’t change.

What advancements have helped scientists challenge the traditional notion of 'living fossils'?

Advancements in genetic testing have allowed scientists to track evolutionary changes at the genetic level, revealing that organisms like horseshoe crabs and crocodiles have evolved significantly, even though their physical forms remain relatively unchanged.

What is the Evolutionary Performance Index (EPI) and how does it relate to living fossils?

The Evolutionary Performance Index (EPI) is a tool developed by researchers to quantify how 'fossil-like' an organism is based on three key factors: the age of its taxonomic group, the number of species in the group, and the branching of its evolutionary tree. This method helps standardize the identification of living fossils.

How did the EPI change the classification of certain species as 'living fossils'?

The EPI confirmed that crocodilians could still be considered living fossils, but other species like sharks and rays, traditionally thought to be living fossils, were excluded because they had undergone too much change over time. However, the broader group of cartilaginous fish still qualifies as fossil-like.

What are Endangered Living Fossils (ELFs), and what criteria must a species meet to qualify as one?

Endangered Living Fossils (ELFs) are species that meet three criteria: they must be endangered or critically endangered, be evolutionarily distinct, and come from an ancient lineage (at least 5.3 million years old). This concept is intended to help prioritize species for conservation.

What are some examples of species that might qualify as ELFs?

Examples of species that might qualify as ELFs include the ginkgo tree, which is the last survivor of its lineage and has adapted to various threats over time, and the coelacanth, a type of lobe-finned fish believed to have been extinct for millions of years before being rediscovered.

Why is it important to protect species classified as living fossils or ELFs?

Protecting these species is crucial because they represent ancient lineages that contribute to biodiversity and could provide valuable insights into both evolutionary and environmental history. Their preservation can help maintain the diversity of the tree of life.

How has genetic research reshaped our understanding of living fossils like the ginkgo and coelacanth?

Genetic research has shown that, despite their ancient appearances, both the ginkgo and coelacanth have experienced significant genetic changes. For example, the ginkgo’s genome has expanded, arming it with defenses against various environmental threats, while the coelacanth’s genetic material shows evidence of exchange with other species.

How do scientists propose to improve the utility of the 'living fossil' concept in modern research?

Scientists propose standardizing the term 'living fossil' using tools like the Evolutionary Performance Index (EPI) and the Endangered Living Fossils (ELF) criteria. This would provide a more consistent and useful way to identify species with ancient lineages that are important for both evolutionary research and conservation efforts.