‘Living fossils’ are unique, not ancient, researchers say

The new measure, called “evolutionary inheritance,” highlights the importance of unique species characteristics, which include physiological adaptations, such as beak variations in different birds, when assessing the richness and complexity of the life.

This is particularly important in the face of rapidly changing pressures on global biodiversity. It may also help address lingering debates in the field, such as whether “living fossils” – species like lungfish, which do not appear to have changed in millions of years – evolve always.

Scientists from Imperial College London, the Zoological Society of London and the University of Canterbury, New Zealand, proposed this new measure to capture the accumulation and loss of specific evolutionary traits over time .

Led by Professor James Rosindell from Imperial’s Department of Life Sciences, the team’s findings are published in the journal Systematic biology.

“The way we measure biodiversity incorporates not only species richness, but also the richness of evolutionarily inherited traits that are often taken for granted,” Professor Rosindell said.

From history to heritage

There are many ways to quantify the biodiversity of an ecological community. One of the simplest is to simply count the number of different species present.

However, in the 1990s, a focus began on evolutionary history, which takes into account the evolutionary distances between species and their degree of relatedness.

Imagine a tree of all life on Earth, where different branches represent different evolutionary lineages. The leaves hanging on the branches are the current species we see today.

Evolutionary history is calculated by considering a set of species and adding up all the branches that connect these species to a common ancestor. The idea is that two more distantly related species are more likely to be distinct from each other than species that diverged from each other relatively recently.

However, a drawback of phylogenetic diversity is that it often fails to fully capture the functional traits that differentiate species physically and ecologically from one another.

Species may be closely related but have very different characteristics, such as Asian and African elephants which have evolved to adapt to their different environments. African elephants have larger ears and more wrinkles on their skin that help them radiate more heat. This is where evolutionary inheritance comes into play.

“With evolutionary inheritance, we’re trying to capture all the unique traits that we expect to exist and that might have all kinds of important uses, but that aren’t yet formally identified and measured,” said Professor Rosindell.

Evolutionary heritage incorporates not only the accumulation of biological characteristics over time, but also their erosion – the gradual loss of characteristics by mechanisms other than extinction.

Not only do species distinguish themselves from each other by acquiring new traits along their evolutionary branches, but they also lose traits that they both inherited from their common ancestor.

This process can be captured by calculations or simulations using an algorithm assigning a random chance of winning or losing an existing trait.

“We’ve captured something that we’ve always been interested in in evolutionary biology, but which we’ve struggled to understand mathematically,” said co-author Dr Will Pearse from Imperial’s Department of Life Sciences.

“Phylogenetic diversity is also considered an indicator of trait diversity, but it ignores that traits not only appear, but are also lost in an evolutionary tree,” said co-author Professor Mike Steel, a biomathematician at the University of Canterbury.

He said: “Evolutionary inheritance is a way to manage this process of winning and losing in an integrated and mathematically natural way. »

Explaining Living Fossils

The team applied their framework to settle a long-standing evolutionary debate around the controversial concept of “living fossils.” Traditionally, living fossils are considered species that appear to have changed little over long geological periods, often retaining a strong physical resemblance to their ancient ancestors.

However, many scientists dislike this term because it implies that the species we see today are literally identical to their ancestors. Professor Rosindell said: “This idea is incorrect; evolution cannot simply be “turned off.” Organisms will continue to mutate and not all will survive to reproduce, so evolution will take place. »

Evolutionary heritage offers a new perspective for understanding living fossils. The new framework defines and identifies living fossils by the uniqueness and rarity of their evolutionary characteristics rather than by their superficial resemblance to ancient species.

The article describes a method in which living fossils are identified not by their total ancestral characteristics, but by the uniqueness or rarity of those characteristics among other living species descended from the same ancestor.

“If we think about a set of ancestral characteristics, some will not survive at all, some will survive in a very small number of living species, and others may be seen today in thousands of descendant species,” he said. said Professor Rosindell.

“It’s the species with rare ancestral characteristics that stand out and are labeled as living fossils according to our method,” he said.

The team is currently working to validate their ideas using genetic and trait data, as well as developing their models for potential use in conservation applications and ecological research.