Episode 70 – Convergent Evolution

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With all the diversity of life past and present, it’s incredible how often evolution repeats itself. Wings, flippers, eyes … all sorts of fascinating features have shown up multiple times in multiple groups of organisms. In this episode, we discuss this very common, curious, and sometimes confusing aspect of natural selection: Convergent Evolution.

In the news
Genetic info reconstructed from proteins in a 1.7-million-year-old rhino tooth.
Baby sea turtle trackways found in South Africa’s Cape South Coast.
A modern sea snake that breathes through a hole in the top of its head.
Theropods may have had special hot-and-cold packs built into their heads.

What is convergence?

Convergent evolution is a side effect of the natural processes of evolution where unrelated species end up resembling one another in behavior or morphology. Though two species may have evolved from very different ancestors, similar selective pressures can lead to them evolving very similar features (for example, birds and bats both evolved from different non-flying ancestors).

This is similar but different from parallel evolution, in which two unrelated but similar evolutionary lineages follow similar evolutionary pathways (for example,. evolving from climbing species to gliding species).

It’s very common to observe convergent evolution in species that occupy similar habitats or niches. Convergent traits are referred to as analogous structures – that is, they are similar, but evolved separately – as opposed to homologous structures, which are shared features inherited from a shared ancestor.

The Evolution of Flight: The wings of pterosaurs, bats, and birds are a perfect example of convergence. While the bones they are using are homologous (all inherited from early vertebrates), the types of wings are analogous (each evolved independently). From TomCatX at Wikimedia

The almost identical body shape and feeding strategy of a hummingbird (left) and hummingbird moth (right) is an excellent example of convergent evolution in body and behavior. Images edit from Wikimedia Commons by

Mosasaurs and metriorhynchids developed very similar body designs for aquatic lifestyles. Both adapted their limbs into paddles and many even evolved vertical tail flukes. Images by Dmitry Bogdanov at Wikimedia Commons.

Sharks (top), ichthyosaurs (middle), and toothed toothed whales such as dolphins (bottom), also all evolved very similar body shapes for marine life. Ichthyosaurs and dolphins took it a step further and bother developed long skiny snouts to catch fish. Image by Internet Archive Book Images at Wikimedia Commons.

The only large animal with a nose horn today is the rhinoceros (bottom right, image by Ikiwaner), but similar structures are seen in ceratopsians and brontotheres (top left and top right, by Nobu Tamura), and the elephant-cousin Arsinotherium (bottom left, by Dmitry Bogdanov). Images from Wikimedia Commons.

None of the animals pictured above are closely related to alligators or crocodiles. Yet all of these croc look-a-likes resemble them with long jaws, short legs, and an aquatic lifestyle. Top left: Prionosuchus was a large amphibian that lived during the Permian. Top right: Phytosaurs were reptilian cousins of archosaurs during the Triassic. Bottom left: Champsosaurus was a Cretaceous reptile. Bottom right: Ambulocetus was a mammal and one of the earliest whales. Images edited from Dr. Jeff Martz (top right) and Nobu Tamura (rest) at Wikimedia Commons.

Not just animals!

Though many call them banana trees, banana plants are actually herbs. They lack wood but have developed a sturdy structure called a pseudostem that allows them to grow to tree-like heights. Image by Brataffe at Wikimedia Commons.

Top: Euphorbias, or spurges, are native to Africa’s dry regions. Bottom: Cacti are found in the New World’s deserts. The two are not related but both are prickly and retain water to survive their harsh environments. Images by Frank Vincentz (top) and Nabin K. Sapkota (bottom) at Wikimedia Commons.

Though convergent evolution is fascinating, it can be tricky to study and understand at times. There are even those who wonder if these numerous examples of very similar organisms actually makes a case for the limits of evolution.

Links

If you’d like to learn more about how organisms can become so similar through convergence check out some of the link below:
Evolutionary Convergences: The Trend Toward Sameness in Metazoan Evolution
– An excellent source on the concept overall
Tail Weaponry in Ankylosaurs and Glyptodonts
Shocking Differences Between Electric Animals – Electric Eels and Rays
Crocodile fossil shows uncanny convergence with dinosaurs
The remarkable convergence of skull shape in crocodilians and toothed whales
Bats and dolphins may have developed echolocation via similar mutations

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If you enjoyed this topic and want more like it, check out these related episodes:

• Episode 6 – Evolution of Flight
• Episode 140 – Horns and Antlers
• Episode 107 – Tusks

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