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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

What is the Molecular Biology?
Service Reply
The branch of biology that deals with the structure and function of the macromolecules (e.g. proteins and nucleic acids) essential to life.
what is the difference between mitosis and meiosis?
Fatima Reply
what is an element
Saidu Reply
Element is any one of the simplest chemical substances that cannot be decomposed in a chemical reaction.
an element is a substance that cannot be broken down into any other substance
explain why only one sperm fertilisers the ovum
Frazzy Reply
its because other sperms are destroyed on the way
what is cell
Dau Reply
Cell is the smallest unit of life
cell refers of the basic, structural and function unit of an organism
smallest functional unit of an organism
explain for me for ecological factors affecting each of aquatic and terrestrial habitats
Ikeh Reply
Temperature, high humidity
temperature,light intensity,Co2
what's meosis
Umoke Reply
meiosis this is the type of cell division which reduces the number of chromosomes in order to form a gamete
meiosis refers to the form of cell division in which a cell divides into four daughter nuclei each containing the same number of chromosomes as the parent cell
cell division where one cell sprits into 4 daughter cells each having half number of chromosomes as parent cell
The end of the linear chromosomes are maintained by
birabwa Reply
is the process of undigested food in body
Enoch Reply
what up nigga
Help me, I'm new here.
What is biology
Hope Reply
What is DNA in full
Deoxyribo Nucleic Acid
deoxyibonucleic acid
Deoxyribonucleic acid
is the study of living things and their interactions with the environment
is the energy production of studying in life (every living things)
de-oxybonuclic acid
Biology is the study of life.
Biology is the study of plant, animal and it's environment
biology is the branch of science that deal with plants and living organism
what's the difference between bi-enial crops and perennial crops
Johnson Reply
Bi-enial crops are crops that live/exist/can last for as long as 2 years while perennial crops are crops that are evergreen and can last eternity or an inestimable amount of time.
what isrespiration
Massa Reply
Mg is very important part of enzymes which deal with DNA. It is a very simple reason but overlooked.
Eric Reply
what mitochondria means
its is the most universal organelle among eukaryotes,it is surrounded by double membrane and in it are foldings and invaginationscalled cristae where areobic respiration takes place
an organelle found in large number in most cell ,in which the biochemical process of respiration and energy production occur
Mitochondria is the power house of a cell
is the energy production in a female hormones
how does a cell look like
Clara 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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