Toads are an evolutionary success story. In a relatively short span of time, they diversified into around 500 species and spread to every continent except Antarctica. Now, Ines van Bocxlaer from Vrije University has uncovered the secrets of their success. By comparing the most home-bound toads with the most invasive ones, she has outlined seven qualities that enabled these amphibians to conquer the world. In a common ancestor, these seven traits came together to create an eighth – a pioneer’s skill are colonising new habitats.
Some, like the harlequin toads, are restricted to such narrow tracts of land that they are vulnerable to extinction. Others, like the infamous cane toads, are highly invasive and notoriously resistant to extinction despite the best efforts of Australians and their sporting equipment. This diversity of lifestyles allowed Bocxlaer to search for characteristics shared by the most pioneering of toad species.
She compared over 228 species, representing just under half of all the known toads, and constructed a family tree that charts their relationships. She showed, as others before have suggested, that the family’s fortunes kicked off in South America, around 35-40 million years ago. This was the start of their global invasion.
Seven qualities make for wide-ranging toads. For a start, the adults don’t have the typical amphibian dependency on constant water or humidity. They have skins that can cope with the drier side of life, giving them a chance to seek out new habitats away from the safety net of moist environments. Secondly, they tend to have fat deposits near their groin, which act as a back-up energy source when food is scarce. Thirdly, they tend to be larger (meaning at least 5 centimetres in length), which also helps to conserve water. Larger animals have larger bladders so they retain more water, and they lose less of it because they have small surface areas for their size.
I live in London. According to Google Analytics, 96% of this blog’s readers make their homes in a different city and 91% live in another country altogether. The fact that most of you are reading this post at all is a symptom of the globalised state of the 21st century.
Through telecommunications, the Internet, free trade, air travel and more, the world’s population is becoming increasingly connected and dependent on one another. And as this happens, the problems that face us as a species are becoming ever more apparent, from our relentless overuse of natural resources to the threat of climate change. But how will globalisation affect our ability to handle these problems? Will it see the cliquey side of human behaviour writ large, or the rise of cooperation on a global scale?
Opinions differ. Some say that globalisation makes the differences between ethnic or geographical groups even starker, strengthening the lines between them. This bleak viewpoint suggests that exposing people to an ever greater variety of world views only reinforces xenophobia. And indeed, recent decades have seen a surge in xenophobic political parties and states seeking independent status.
Others take a more optimistic stance, arguing that in a globalised world, people are more likely to find a sense of common belonging and concepts of ethnicity or nationhood become less relevant. After all, recent decades have also seen an increase in foreign aid to developing countries and human rights campaigns.
Nancy Buchan form the University of South Carolina has used a clever psychological game to show that the latter perspective is stronger. Her group recruited volunteers from six countries across five continents and asked them to play a game where they could cooperate with each other at local or global levels. She found that people who were more connected internationally, or who came from more globalised countries, were more likely to work together at a global level. Globalisation, it seems, breed cosmopolitan attitudes, not insular ones.