Bird DNA Leads to Strange Family Tree
2016-01-06 05:47
中學科技 2015年10期
Birds of a feather may flock together， but their appearances can be deceiving. Birds that look similar may not be as closely related as field guides might suggest. That's the conclusion of a new study. When researchers grouped birds by DNA， rather than looks， they turned up some surprising family members.
Falcons， for example， hunt small animals. But the new study finds these birds are more closely related to parrots than to hawks， eagles and other birds of prey. Another surprise： flamingos. The closest cousin of these brightly colored waterbirds is the grebe， a diving bird that looks like a duck. In fact， flamingos and grebes occupy a lonely branch on the family tree. And both of these birds are more closely related to pigeons than to any other waterbirds.
It's not uncommon for birds that look or behave differently to in fact be closely related， says the neuroscientist at Duke University， helped lead the new research. And， he points out， bird species with different ancestors may develop similar looks and behaviors. This can happen when animals， over many generations， adapt to similar lifestyles.
A tree of life uses a branched， treelike diagram to depict how organisms relate to one another. Species change slowly over time， through a process known as evolution. On a tree of life， the outer， twiglike branches represent species alive today. Follow those smaller twigs to where they branch off from thicker limbs and you find the ancestors of today's species.
Early trees of life grouped birds together by similarities or differences in their bones and body parts. More recently， scientists have begun focusing on the animals' DNA. The scientists looked at this DNA in a big way.
Inside almost every cell of an organism is information that is passed from parents to their offspring. This information is “written” using a molecule called DNA. It instructs cells on how to grow and function. When a species evolves， its DNA changes.
In 2008， the research team studied 19 different segments of DNA from 169 bird species. Their tree of life suggested that falcons and hawks， and grebes and ducks， were only distantly related. Those surprises were confirmed by the new study. Scientist Jarvis and his team used cutting-edge technology and much more genetic data to get an even clearer picture of bird DNA.
1. What can be inferred from the passage？ ____.
A. Species that look similar must be closely related
B. Birds that flock together must belong to the same family
C. It is possible that birds looking quite different may belong to the same branch on a family tree
D. Falcons are more closely related to other birds of prey than to parrots
2. What is NOT true about flamingos？ ____.
A. Their closest cousin is the diving bird， grebe
B. They are brightly colored waterbirds
C. They are more closely related to pigeons than to any other waterbirds
D. They usually inhabit high， dry places
3. Why do species with different ancestors have similar looks and behaviors？ ____.
A. Because they adapt to similar lifestyles
B. Because they mate with each other and produce common offspring
C. Because they have the same DNA
D. Because they occupy the same branch on the family tree
