From Evolutionary Advantages to Fatal Threats in Turtles

Turtles have inhabited the Earth for over 100 million years. Their most distinctive feature, the shell, stands as a testament to the long evolutionary history of this lineage. However, in the age of humans, this very shell—along with other evolutionary advantages accumulated over millions of years—has paradoxically become a disadvantage, intensifying the risk of extinction faced by turtles today.

Wildlife is an essential component of ecosystems, yet human activities such as overexploitation, habitat destruction, and the introduction of invasive species are posing severe threats to biodiversity. Many species have experienced rapid population declines, and numerous others have already gone extinct. It can be said that humans have become the primary driver of global biodiversity loss. Among vertebrates, members of the order Testudines (turtles and tortoises) are heavily targeted due to their high value as food, cultural items, and pets. Each year, approximately 800,000 individuals are traded globally, making them the second most threatened group of vertebrates after primates.

Today, there are over 360 extant species of Testudines, representing a highly successful evolutionary lineage. Their success is attributed to several key traits, including long lifespans, high environmental tolerance and adaptability, protective shells, and temperature-dependent sex determination. However, in the Anthropocene, these once advantageous traits have turned into liabilities.

Schematic diagram showing the transformation of turtles’ advantages into disadvantages（image source：卜榮平， 李天明， 施海濤. （2023），採用 CC BY 4.0 授權）

The long lifespan and relatively high reproductive potential of turtles allow them to adapt to environmental changes. However, longevity has also led to cultural beliefs—such as the idea that consuming turtles can promote human longevity—resulting in their exploitation, for example in traditional Chinese medicine. Moreover, their long lifespan means that turtles take a long time to reach sexual maturity. Many individuals are captured before reproducing, and even those that reach maturity are often harvested before producing sufficient offspring, leading to population decline and insufficient recruitment.

Turtles also possess a strong tolerance for extreme environmental conditions, allowing them to survive in diverse habitats and endure long periods without food. While this trait has helped them persist through natural selection, it also makes them easy targets for commercial farming and global wildlife trade. Their ability to survive long-distance transport further facilitates their exploitation.

The shell, a key adaptation for defense against predators, has been crucial to the long-term survival of turtles. However, it also restricts mobility—especially in terrestrial tortoises—making them slow and easy to capture. Over the past 500 years, human hunting has driven at least five large tortoise species to extinction. Additionally, the shell’s aesthetic appeal has made turtles popular in the pet trade.

Yellow-footed tortoise（image source：Maarten Sepp，採用 CC BY-SA 4.0 授權）

Turtle sex determination depends on temperature, a reproductive strategy that has functioned effectively throughout evolutionary history. However, rapid human-induced climate change now disrupts this mechanism. Due to their long generation times and limited mobility, turtles are unable to adapt or migrate quickly enough. As a result, skewed sex ratios are emerging, posing a serious threat to population viability.

In summary, turtles face multiple, compounding threats to their survival. Addressing this crisis requires banning commercial exploitation of wild turtle populations, strengthening wildlife protection laws, and improving enforcement against illegal trade. Additionally, further ecological research is needed to better understand turtle habitats and to mitigate habitat destruction and pollution. Reducing greenhouse gas emissions is also critical—not only for turtle conservation but for humanity as a whole. Finally, public education plays a vital role in raising awareness and reducing illegal activities, ultimately contributing to the conservation of global turtle diversity.

（Author: Bai Leng）

reference：

卜榮平， 李天明， 施海濤. （2023）.The evolutionary advantages of chelonians are making them vulnerable to extinction in the Anthropocene. Integrative Conservation.