For years scientists have been studying evolution and common decent. From

Darwin to the modern day scientists humans have been trying to find out about how

the world has evolved. Even with modern day technology scientists have trouble

finding out how evolution works. Common descent can be proved in multiple ways.

Scientists use fossils, embryology, comparative anatomy, biogeography, and

biochemistry to give evidence that common descent has occurred.

One of the most obvious ways to study extinct animals is to take a look at

fossils. People can look at fossils and see how the animals looked in the past. These

fossils provide scientists with a record of ancient life. There are 2 kinds of fossils

there are fossils of animals that have become extinct and animals that have

undergone little change. By looking at these fossils you can see animals that look half

like a bird and half like a alligator. Seeing these fossilized animals show that over

time they have evolved from one type of creature into many therefor proving that

common descent is true. Although fossils are a great way to prove common descent

has occurred there are also many other ways.

Biochemistry is another way to prove common descent. Biochemistry is

details from many organisms that trace back to a single group of organisms.

Scientists use many different chemical tests to show that all organisms have similar

DNA. They also find that all organisms have similar proteins. By finding that they

have DNA that is similar you can then conclude that these animals have a common

ancestor.

Biogeography is a way of looking at the way plants and animals have evolved

from their geographical distribution. In 1876 a man by the name of Alfred Wallace

wrote a book about Biogeography. This book states that there are 6 different regions

of the earth. Each Biogeographical region has its own specific organisms that are

unique to that region. A major factor that affects where these regions are is the

environment. Animals such as amphibians and reptiles are in almost all of these

regions because of the time that they arose. These animals came to be around the

time when the earth started to change from on super continent to many smaller ones.

Mammals however arose after the breakup and are specific to only a few of these

regions. Scientists look at where these animals came from and fossils to prove that

they have a common descent.

Scientists use embryology to look at organisms before they are fully

developed to find similarities. For example if you look at the embryo of a human a

bird and a lizard you will find that they look almost identical at first but as they

grow the embryo starts to change and features start to form. organisms that are

embryologically similar but have different functions are called homologus

structures. By looking at the lizard the human and the bird embryo and finding that

they have homologus structures you can then prove that they have a common

ancestor. For example they all have the same bone types in the arms or legs. These

homologus structures show scientists that these animals have come from a common

decent.

Another way for scientists to prove that certain organisms have come from a

common ancestor is to compare the anatomy of the organisms. For example scientists

can look at a birds legs and the scales of a crocodile. The legs of the bird have the

same scales as the crocodile does all over its body. this is a good way to prove that

these two animals have come from a common origin. The scientists look for things

that are the same in any animal. If you look at a monkey and the way their arms and

hands are you can see the resemblance to a human. This suggests that we have a

common ancestor. This is one of the easiest ways to find out whether two or more

organisms are related.

Scientists use all these methods to show that certain organisms are related.

They use fossils, biochemistry, biogeography, comparative anatomy, and embryology

to show common descent. All of these methods have their advantages and

disadvantages, but they all help prove that common decent is a feasible theory.