Challenging Evolutionary Assumptions: Study on Static Traits in Lizards Questions Conventional Wisdom in Evolutionary Biology
Investigating Evolutionary Stagnation with Anole Lizards
Credit: Jon Suh
Through a three-year observational study involving tracking technology affixed to lizard legs, James Stroud from the Georgia Institute of Technology has shed light on why many species remain morphologically consistent over geological time scales, seemingly contradicting Charles Darwin’s postulation of continuous evolution.
Charles Darwin theorized that constant evolutionary changes lead species to adapt in the struggle for existence. However, skeptics among his contemporaries questioned this claim. They wondered how it was possible for identical fossils of the same species, located in the same geographic area but separated by 50 million years, to exist if evolution is ceaseless.
The landscape of evolutionary biology underwent a significant shift in the past four decades, with a multitude of studies demonstrating that evolution could occur at an accelerated pace, even between successive generations. While these findings excited scholars in the field, they also reinforced the original conundrum: Why do the majority of species remain unchanged over extensive periods of geological time?
Decoding Evolutionary Stasis
Credit: Day’s Edge Prods
This contradiction is commonly known as the “paradox of stasis,” a topic James Stroud, an assistant professor in the School of Biological Sciences at the Georgia Institute of Technology, aimed to explore. Stroud’s comprehensive field study examined the natural evolutionary process across multiple lizard species and potentially identified a solution to one of the most puzzling challenges in evolutionary biology.
The research was featured prominently in the Proceedings of the Natural Academy of Sciences.
Addressing the Contradiction
“The term paradox is apt here because the phenomenon appears counterintuitive,” Stroud observed. “The prevailing hypothesis has been that natural selection operates to maintain the average phenotype of a species, yet empirical studies almost invariably fail to detect such ‘stabilizing’ selection.”
Field Research on Lizard Populations
Stroud initiated a meticulous field study involving four distinct species of Anolis lizards on a minor island located within the Fairchild Tropical Botanic Gardens in Coral Gables, Florida. Over five separate phases, Stroud caught and monitored each lizard on the island, meticulously documenting their survival rates.
Working around the clock, Stroud and his team utilized specialized fishing poles equipped with minute lassos to carefully capture the lizards. After documenting each lizard’s original location, they took a series of measurements including head size, leg length, body mass, and even the adhesive qualities of the lizard’s toes.
Periodic Monitoring and Data Analysis
Every six months over the course of three years, Stroud and his team revisited the study, capturing the same individual lizards for updated measurements and tracking which ones survived. By collating data across various time frames, Stroud was able to correlate physical traits with survival rates, thereby gaining a holistic understanding of how natural selection acted on the lizard community.
Unexpectedly, Stroud discovered that the supposed “stabilizing” form of natural selection was exceedingly uncommon. Instead, the form and criteria for survival among the lizards varied substantially over time. In some years, lizards with longer legs had better survival rates, while in other years, those with shorter legs were more likely to survive. At times, no discernable pattern was evident.
Unprecedented Findings and Implications
Stroud’s study broke new ground by offering unparalleled insights into the mechanics of selection at a community level, achieved through an unprecedented level of detail. Typically, the scientific community hesitates to engage in long-term field studies due to the significant resources required, which has led to limited understanding of community-level evolution.
“Evolution is not a stagnant process, even if phenotypic traits appear unchanging over long durations,” Stroud remarked. “It is crucial to our comprehensive understanding of life on Earth, not only for comprehending the distribution and characteristics of flora and fauna but also for understanding how life adapts in a human-dominated world.”
According to Stroud, the scarcity of long-term field studies has given rise to a skewed perception of evolutionary processes.
“For many years, evolutionary biologists have been grappling with the perplexity of the paradox of stasis,” said Stroud. “This study suggests that the solution may not be overly complex; it simply necessitated a sufficiently long study in a natural environment to uncover it.”
Reference: “Fluctuating selection maintains distinct species phenotypes in an ecological community in the wild” by Stroud, J.T., et al., 9 October 2023, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2222071120
Frequently Asked Questions (FAQs) about paradox of stasis
What is the main focus of James Stroud’s study?
The main focus of James Stroud’s study is to explore the “paradox of stasis,” a puzzling phenomenon in evolutionary biology where many species appear morphologically consistent over extended periods, despite the theory of constant evolution. The study aims to resolve this apparent contradiction through a meticulous, long-term field study on Anolis lizards.
What is the “paradox of stasis”?
The “paradox of stasis” refers to the puzzling observation that many species remain morphologically unchanged over geological time scales, even when theories of evolution suggest they should be continuously evolving. This paradox has been a subject of debate and inquiry among evolutionary biologists.
Where was the field study conducted?
The field study was conducted on a small island within the Fairchild Tropical Botanic Gardens in Coral Gables, Florida.
What methods were used to capture and study the lizards?
Stroud and his team used specialized fishing poles equipped with tiny lassos to capture the lizards. Once captured, a series of measurements were taken, including head size, leg length, body mass, and the adhesive qualities of the lizard’s toes. These lizards were then monitored over a period of three years.
How often was the data collected?
Data was collected every six months over a three-year period. The same individual lizards were captured for updated measurements and survival tracking.
What were the key findings of the study?
One of the key findings was that the commonly assumed “stabilizing” form of natural selection was exceedingly rare. Instead, the criteria for survival among the lizards varied substantially over time. Overall, natural selection was found to be extremely variable, effectively maintaining species’ traits across the studied period.
How does this study contribute to the field of evolutionary biology?
This study breaks new ground by offering unprecedented insights into how natural selection works at a community level. It suggests that long-term field studies are necessary to fully understand the mechanisms of evolution, and challenges the notion that stabilizing selection is the primary force maintaining species’ traits over time.
Who published the study and where can it be found?
The study was published in the Proceedings of the Natural Academy of Sciences and can be accessed through their archives, with the DOI reference 10.1073/pnas.2222071120.
More about paradox of stasis
- Proceedings of the Natural Academy of Sciences
- About James Stroud
- Fairchild Tropical Botanic Gardens
- Introduction to Evolutionary Biology
- Understanding Natural Selection
- [The Paradox of Stasis: A Literature Overview](https://academic.oup.com/sysbio/article/66/3/ paradox-of-stasis)
- Anolis Lizards: An Introduction
- Charles Darwin and the Theory of Evolution
- Understanding the DOI System