Monday, March 8, 2010

Convergent Evolution

One of the most interesting points Coyne makes is that similar environments will cause similar traits in species that aren't related very closely. He does this on pgs. 92-94. This is called convergent evolution. The idea is that natural selection will make animals on two different sides of the world but in similar environments acquire similar traits. Examples he uses include similarities between many animals that have marsupial equivalents in Australia. What other examples are there of convergent evolution around the world? This could be similarities between any two organisms. What environmental pressures are theorized to have caused the similar traits?


  1. Another example of convergent evolution is the camouflaging white coloration shared by diverse Arctic animals such as the polar bear and the snowy owl. These species do not have common ancestors; however, they both have similar white coloration that allows them to hide from predators in the snowy white environment. Cacti and euphorbs also have convergent traits. Euphorbs colonized the Old World and the cacti colonized the Americas. Both species live in desert environments that are very dry climates. Due to the fact that both are plants, it makes sense that they are tough and leafless and have a fat stem to store water. Leaves would only hurt them through major water loss. "One of the best examples of convergent evolution involves how birds, bats, and pterosaurs (all different species that evolved along distinct lineages at different times) learned to fly. Importantly, each species developed wings independently. These species did not evolve in order to prepare for future circumstances, but rather the development of flight was induced by selective pressure imposed by similar environmental conditions, even though they were at different points in time."( It makes sense that species living in similar environments, even if they are on opposites sides of the world, would adapt similar traits because species must adapt to their environment in order to have the best chances of survival and reproduction. Species want to keep homeostasis. One way to do this is through regulation of certain parts of their bodies and adaption of parts of their bodies so that they can maintain the normal balance they need in order to survive. It is easy for a species to adapt its body since it can't change its environment without migrating, which could put itself in a danger and lower its chances of surviving. An individual can regulate its body through the turning on and off of genes so that different proteins are being synthesized and carrying out the necessary functions to maintain homeostasis or hormones can be regulated by various negative and positive feedback mechanisms. ( lists reasons for why homeostasis is advantageous to organisms. "Homeostasis has survival value because it means an animal can adapt to a changing environment. It can deal with the temperature difference you face when you step our your front door. The body will attempt to maintain a norm, the desired level of a factor to achieve homeostasis. However, it can only work within tolerable limits, where extreme conditions can disable the negative feedback mechanism." All of these regulation techniques keep an individual in balance so that they can survive best in their environment. Species that live in similar environments must do similar things in order to survive because many species need the same types of things. Species in a dry environment need to regulate water balance. They do so by altering their bodies so that they don't loose too much water.

  2. In addition to regulation, convergent evolution also embodies the idea of structure and function. Convergent evolution occurs when separate species in different areas of the world evolve similar traits as they adapt to similar environments. Often times, certain structures are ideal to function in certain environments. Thus, these structures would clearly show up more frequently in various times and locations in evolutionary history.

    As previously mentioned, wings are a prime example of convergent evolution. Bats, birds, and pterodactyls evolved in different segments of evolutionary time as well as various ecosystems. Each of these specie's forelimbs evolved into wings in order to meet the demands of the environment. Common reasons for the evolution of flight in various organisms include escaping from predators, catching speedy prey, moving from place to place, and gaining access to new food sources. These wing functions could not be possible without the unique anatomical structure of the wing. The wing is made of hollow bones essential for a bird to be airborne; the wing is in the shape of an airfoil, which creates a pressure difference that lifts the bird; the wing has an adapted shoulder blade, which allows the large range of motion necessary for flapping. Convergent evolution clearly dictated the creation of the wing in various parts of the globe. Still, birds of differing habitats have slightly different wings, which make them more adapted to their environment. For instance, penguins' bones are much heavier than the average bird because penguins utilize their wings for diving rather than flying. Once again, structure dictates function.

    Another scenario of structure influencing function in convergent evolution is different kinds of anteaters. Anteaters can be found in as distant of locations as Australia, America, and Africa. These organisms are not closely related yet they all developed the perfect instruments to survive on an ant diet. Anteater adaptations include "a long, sticky tongue, few teeth, a rugged stomach, and large salivary glands" ("Convergent Evolution"). Once again, convergent evolution called for similar structures in starkly different parts of the world. These similar structures perform similar functions because although ecosystems may vary, the niches within them may not.