Faster evolution means faster extinction?

01

Biodiversity is uneven, as evidenced by the fact that many equally ancient sister evolutionary branches contain both many and few species.

It is generally believed that in the evolution of biodiversity, many large evolutionary branches emerged through rapid evolution and have higher biodiversity, while smaller branches experienced slower evolution and have lower biodiversity.

However, in the 1940s, the famous paleontologist George Gaylord Simpson put forward a contradictory view in his classic book "The Rhythm and Pattern of Evolution".

Simpson believes that rapid evolution may lead to instability and extinction, while slow evolution can lead to higher biodiversity. Because high-rate evolution is unlikely to last for a long time, it can make evolutionary branches very unstable, leading to extinction or turning to a slower evolutionary rate. By studying the basic patterns of evolution within the framework of Darwin's theory of evolution, he observed that many rapidly evolving species actually belong to unstable groups that are likely to adapt to rapidly changing environments.

It's a challenging idea. Now, a new study published in the journal Paleontology has found evidence for Simpson's claim by examining lizards and some of their closest relatives. In simple terms, their results suggest that the faster you evolve, the faster you go extinct.

02

In the new study, researchers analyzed a group of animals called Lepidosauria, which includes lizards, snakes and some of their close relatives. Lepidosauria originated in the early Mesozoic era 250 million years ago and can be divided into two main groups: Squamata and Rhynchocephalus. Squamata has developed into more than 10,000 species of modern lizards and snakes, while Rhynchocephalus has only a single species left today - the Rhynchocephalus (also known as the New Zealand giant lizard).

The evolutionary tree of tuatara, lizards and snakes. During the age of the dinosaurs, tuatara's extinct relatives evolved rapidly, while lizards and snakes evolved slowly. | Image credit: Dr Tom Stubbs

Before this study, the researchers expected to find traces of slow evolution in rhynchocephalans and fast evolution in squamates. However, what they observed was exactly the opposite of what they expected. They found that squamates had slow evolutionary rates for the first two-thirds of their evolutionary history, while their sister branch, rhynchocephalans, which today consists of only one species, showed fast evolutionary rates in the past.

The researchers investigated the speed of body size change in these early reptiles and found that while some squamates (especially those with a special lifestyle) evolved rapidly during the Mesozoic Era, the rhynchocephalans evolved at a faster rate, with an average rate significantly faster than squamates, about twice the background rate. This finding was far beyond the researchers' expectations.

During the late Mesozoic, all modern lizards and snakes emerged and began to diversify, living alongside dinosaurs but probably not in ecological contact with them. Most of these early lizards were small and ate bugs, worms, and plants.

For about 200 million years, the rate of evolution of lizards and snakes (Squamata) (blue) was much slower than that of rhynchocephalans (green), a situation that has only reversed in the last 50 million years or so. The red line shows the average rate of evolution of all Lepidosaurs over geological time. | Image credit: Armin Elsler

After the extinction of the dinosaurs, about 66 million years ago, both rhynchocephalians and squamates suffered greatly. However, the number of squamates recovered later, while rhynchocephalians, which had been "innovators" and "fast evolvers" for most of the Mesozoic, actually declined significantly before the end of the Mesozoic, and after that, the whole dynamic changed.

03

We have all heard the story of "The Tortoise and the Hare" from Aesop's Fables, in which the fast rabbit loses the race, while the slow tortoise crosses the finish line first. The message of this story is that only slow and steady wins the race. In fact, since the time of Darwin, biologists have been arguing about whether evolution is more like the rabbit or the tortoise in "The Tortoise and the Hare". Are many biological populations composed of a large number of species the result of rapid evolution in a short period of time, or the result of slow evolution over a long period of time?

According to the latest research results, the slow and steady way of survival allowed the squamates in the Mesozoic era to win the race; while the rapidly evolving and prosperous rhinoceros lost with only one survivor. For rapidly evolving groups of organisms, sometimes they can stabilize and survive well; but in more cases, their extinction rate will be very fast, as fast as the rate at which new species appear, and their ending is like a rabbit taking a nap in the middle of a race.

In addition, according to Simpson's prediction, species that evolve slowly may also slowly go extinct and be more successful than fast-evolving species for a longer period of time, just like the slow-moving but persistent tortoise in the fable. Next, the researchers hope to explore the situation in more biological groups to prove that rapid evolution leads to short-term high diversity but ultimately leads to long-term low biodiversity.

#Creative Team:

Text: Xiaoyu

#Reference source:

http://bristol.ac.uk/news/2021/november/rapidly-evolving-species-more-likely-to-go-extinct.html

https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12579

#Image source:

Cover image: University of Bristol

Source: Principle (ID: principia1687)

This article has been authorized. Please contact the original author for reprinting.