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By the end of this section, you will be able to:
  • Compare homologous and analogous traits
  • Discuss the purpose of cladistics
  • Describe maximum parsimony

Scientists must collect accurate information that allows them to make evolutionary connections among organisms. Similar to detective work, scientists must use evidence to uncover the facts. In the case of phylogeny, evolutionary investigations focus on two types of evidence: morphologic (form and function) and genetic.

Two options for similarities

In general, organisms that share similar physical features and genomes tend to be more closely related than those that do not. Such features that overlap both morphologically (in form) and genetically are referred to as homologous structures; they stem from developmental similarities that are based on evolution. For example, the bones in the wings of bats and birds have homologous structures ( [link] ).

 Photo a shows a bird in flight with a corresponding drawing of a bird wing. Photo b is a bat in flight with a corresponding drawing of a bat wing. Both the bird wing and the bat wing share common bones, analogous to the bones in the arms and fingers of humans. However, in the bat wing, the finger bones are long and separate and form a scaffolding on which the wing’s membrane is stretched. In the bird wing, the finger bones are short and fused together at the front of the wing.
Bat and bird wings are homologous structures, indicating that bats and birds share a common evolutionary past. (credit a: modification of work by Steve Hillebrand, USFWS; credit b: modification of work by U.S. DOI BLM)

Notice it is not simply a single bone, but rather a grouping of several bones arranged in a similar way. The more complex the feature, the more likely any kind of overlap is due to a common evolutionary past. Imagine two people from different countries both inventing a car with all the same parts and in exactly the same arrangement without any previous or shared knowledge. That outcome would be highly improbable. However, if two people both invented a hammer, it would be reasonable to conclude that both could have the original idea without the help of the other. The same relationship between complexity and shared evolutionary history is true for homologous structures in organisms.

Misleading appearances

Some organisms may be very closely related, even though a minor genetic change caused a major morphological difference to make them look quite different. Similarly, unrelated organisms may be distantly related, but appear very much alike. This usually happens because both organisms were in common adaptations that evolved within similar environmental conditions. When similar characteristics occur because of environmental constraints and not due to a close evolutionary relationship, it is called an analogy    or homoplasy. For example, insects use wings to fly like bats and birds, but the wing structure and embryonic origin is completely different. These are called analogous structures ( [link] ).

Similar traits can be either homologous or analogous. Homologous structures share a similar embryonic origin; analogous organs have a similar function. For example, the bones in the front flipper of a whale are homologous to the bones in the human arm. These structures are not analogous. The wings of a butterfly and the wings of a bird are analogous but not homologous. Some structures are both analogous and homologous: the wings of a bird and the wings of a bat are both homologous and analogous. Scientists must determine which type of similarity a feature exhibits to decipher the phylogeny of the organisms being studied.

Questions & Answers

complete the table below based on the levels of biological organization
Lovely Reply
Give me Examples of living thing which have 2 or more flagella?
Mahesh Reply
insect and plants
qax
bacteria and chlamydompnas
Berhanu
reproduction it's full meaning
Gift Reply
full meaning of ATP
Gifty
A life process in which living things increase their population through sexual or non sexual intercouse
Danisha
please explaination
Daniel
Gifty ATP means Adenosine tri phosphate
Mahesh
the process by which organisms produce their own kind.
Berhanu
reproduction is the process where living organisms producess their offspring
jerry Reply
what is reproduction
Nmesoma Reply
why some kinds of students are failed
Ahmadi Reply
lack of concentration
Faith
lack of guidance and counseling
ali
what's the divination of openstax
John
don't mind about reading
aine
lack of focus
Afolayan
What is the meaning of optic
Kisaky Reply
Giving a specific section of the alimentary canal,describe 3 ways in which physical digestion occurs.
Kisaky
mouth when chewing
ephraim
what is population
Ivy Reply
total number of people living in an area
FILDA
a number of people lives in one catigorize area or named area
Oburak
what is a cell
Chiko Reply
basic and functional unit of life
Edwin
cell is tissues that makes up functional life in human or un animal.
Oburak
is the smallest basic unit of life.
Kisaky
Is the smallest baic unit. o
Kisaky
why cell is very important to human body
Ahmadi
what is diffusion
Henry
diffusion is a process of mix of particles from higher concentration to the lower one,to make the body functional normal
Adam
what is effusion
Mahesh
what is soil
FILDA Reply
Is the finely divided material covering the earth crust.
Kisaky
is the upper moist of layer of the earth surface
Ahmadi
what is reducing sugar
Erica Reply
in genetics which disease is also termed as the queen disease
Phinihas Reply
what are the types of cell
Teye Reply
prokaryote ,eukaryote, akaryotes
bonney
what is akaryotes ?
Chriscia
multicellular and unicellular
Edwin
akaryotes are organisms that function as eukaryotes and prokaryotes
Edwin
akaryotes are cell with no nucleus
Edwin
biology is the study of living organisms
bonney Reply
what's the divination of open stax?
John
biology is designed for multi- semester biology course for science Major
John
what are the important of cells in the body
Nharnhar Reply

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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