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Why do zebras have stripes? This question has been researched and hypothesized for many years. Up until now there have been four main theories for why one of our favorite African animals has its black and white coat. The prevailing theories were that the stripes a) confused predators, b) protected against biting insects that carried disease c) helped to control and maintain body temperature, and d) were used as a way of identifying with their herd. Previous research has focused on testing one of these hypotheses at a time. The latest study from a team out of UCLA's department of ecology and evolutionary biology tested a bigger set of hypotheses against one another to come to their conclusion.

Zebra (photo credit: Angela Sevin)

The research team, led by Brenda Larison, determined that the temperature of the area the zebras lived in was the biggest factor determining their striping pattern. Larison and others have committed themselves to learning more about the striping pattern of zebras, with their cutting-edge research including DNA sequencing to determine what genes code for striping. In this particular study, Larison's team observed the plains zebra, which is the most common of the three species of zebra. This zebra has a wide range of stripe patterns. By comparing sixteen different areas where the zebras lived, the scientists found that the zebras in colder areas had lighter, narrower and fewer stripes. Often these zebras did not have striping on their legs. In the warmer regions the zebras had bolder striping patterns and the stripes covered their entire bodies. This is the first evidence that we have to show that the black and white patterns on the zebras have to do with thermoregulation, or maintaining body temperature.

Other research, that has yet to be published, also investigates the zebra's body temperature. Daniel Rubenstein, one of the world's leading zebra researchers, has found evidence suggesting that the external body temperature of the zebras is about five degrees Fahrenheit colder than animals of similar size, such as antelopes. These comparable animals do not have stripes but are found living in the same areas as the zebra. This study definitely corroborates the idea of the stripes as an important factor in thermoregulation in different climates.

It takes a lot of research to make a determination that is not theoretical in evolutionary biology. There is no doubt that the prevailing theories of zebra striping do have some relevance, but having some conclusive evidence based on a combination of factors is welcome information in piecing together this evolutionary puzzle.

Read more:

Science Daily: "Why do zebras have stripes? Temperature counts"
Royal Society of Open Science: "How the zebra got its stripes: a problem with too many solutions"
Science World Report: "Why do Zebras Have Stripes? Scientists Uncover the Evolutionary Answer"

Zebra and Animal Coloration Resources and Activities:

Plains Zebra- Animal Information
Purdue Extension: Coloration Exploration Lesson Plan
Discovery Education: Animal Colors and Shapes
Kids Discover: African Safari

photo credit: chefranden

Scientists love to organize things into categories. Scientists also love to re-organize the same things into different categories. This happens constantly when it comes to phylogeny, or the history of the evolution of a species. Often the re-organization takes place after new clarifying evidence emerges. Last week a series of papers were published in the journal Science, after a study that was literally an international collaboration took place over the course of the past four years. Scientists joined forces globally to map and analyze the genomes, or the genetic material, of 48 different bird species. With these new genetic maps they were then able to reorganize the family tree of many bird species. What they found was surprising, but sensible.

The new evolution map (see it in this article) shows very clearly the population and diversity explosion that resulted after a large asteroid collided with Earth and caused mass extinction about 66 million years ago. Although land birds suffered during this time, flying birds flourished. With this new data it is obvious that prehistoric birds evolved into just a few groups. Paleognathae branched off as two groups of land birds, the ostrich and tinamous, a group of land birds found in Mexico, Central and South America. Another large group, Neognathae, branched twice. One branch is the Galloanseres, which are land fowl and water fowl, birds like chickens and ducks. The other branch is the Neoaves, which includes all other birds. So, lets put aside the scientific names and break this down- unless you are a land bird or fowl, you are very closely related (genetically speaking) to all other birds. Of course there are many groups within Neoaves: birds of prey, water birds, songbirds, etc. What is mind-boggling is how many different species evolved after that asteroid hit. Scientists have seen a similar pattern in the evolution of mammal species. Mammals and birds capitalized on filling the newly open niches left behind by the dinosaur's extinction.

Scientists learned a lot through this collaboration. Other papers in the series dealt with evolutionary connections in vocal learning, bird's loss of teeth and the cold tolerant adaptations of penguins. Although science is often collaborative, it is rare that it is on such a grand scale. I believe that due to cooperation on the part of scientists globally these studies were able to happen much more quickly than they usually do. Hopefully this will spur many other team efforts. Science certainly does not happen in a bubble!

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