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By the end of this section, you will be able to:
  • Define species and describe how species are identified as different
  • Describe genetic variables that lead to speciation
  • Identify prezygotic and postzygotic reproductive barriers
  • Explain allopatric and sympatric speciation
  • Describe adaptive radiation

Although all life on earth shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and have offspring that can then successfully reproduce. Scientists call such organisms members of the same biological species.

Species and the ability to reproduce

A species    is a group of individual organisms that interbreed and produce fertile, viable offspring. According to this definition, one species is distinguished from another when, in nature, it is not possible for matings between individuals from each species to produce fertile offspring.

Members of the same species share both external and internal characteristics, which develop from their DNA. The closer relationship two organisms share, the more DNA they have in common, just like people and their families. People’s DNA is likely to be more like their father or mother’s DNA than their cousin or grandparent’s DNA. Organisms of the same species have the highest level of DNA alignment and therefore share characteristics and behaviors that lead to successful reproduction.

Species’ appearance can be misleading in suggesting an ability or inability to mate. For example, even though domestic dogs ( Canis lupus familiaris ) display phenotypic differences, such as size, build, and coat, most dogs can interbreed and produce viable puppies that can mature and sexually reproduce ( [link] ).

Photo a shows a poodle with curly short fur. Photo b shows a cocker spaniel with long, wavy fur that has light brown parts and cream-colored markings on the face, forepaws, belly, hind legs, and tail. The poodle has longer legs than the cocker spaniel. The cockapoo in photo c has curly hair, like the poodle, and short legs, like the cocker spaniel.
The (a) poodle and (b) cocker spaniel can reproduce to produce a breed known as (c) the cockapoo. (credit a: modification of work by Sally Eller, Tom Reese; credit b: modification of work by Jeremy McWilliams; credit c: modification of work by Kathleen Conklin)

In other cases, individuals may appear similar although they are not members of the same species. For example, even though bald eagles ( Haliaeetus leucocephalus ) and African fish eagles ( Haliaeetus vocifer ) are both birds and eagles, each belongs to a separate species group ( [link] ). If humans were to artificially intervene and fertilize the egg of a bald eagle with the sperm of an African fish eagle and a chick did hatch, that offspring, called a hybrid    (a cross between two species), would probably be infertile—unable to successfully reproduce after it reached maturity. Different species may have different genes that are active in development; therefore, it may not be possible to develop a viable offspring with two different sets of directions. Thus, even though hybridization may take place, the two species still remain separate.

Photo a shows a picture of the African fish eagle in flight, and photo b shows the bald eagle perched on a post.
The (a) African fish eagle is similar in appearance to the (b) bald eagle, but the two birds are members of different species. (credit a: modification of work by Nigel Wedge; credit b: modification of work by U.S. Fish and Wildlife Service)

Questions & Answers

what is biology
enock Reply
what type of fluid is filled in hydroskeretal system
Ngenda Reply
The phenomenon by which Protoplasm of a cell shrinks from the wall is 
test Reply
which vein connective from harm to Brian
Burton Reply
which nevel succulate blood system from harm to hear
Burton
if an organism is cartilaginous is fully capable of a protecting the internal organs
Verah Reply
what is different between cell and tissue
Rose Reply
cell is the functional and structural unit of life while tissue is a group of cells aggregate to perform a similar or particular function
Tajudeen
cell is the basic unit of life while tissue is group of related cells that perform the same function Eg. the nerve tissue is made up of nerve cells
AAGifty
please what is meant by mutation
Kyere Reply
mutation is the change in DNA which results in the evolution
Shshank
what is binominal nomenclature?
Furaha Reply
the system of naming organisms depending on their xtics of origin
Vincent
The system of naming organisms using two-words Latin names
Agyeiwaa
what is the fate of reduced NAD in cell metabolism
namirembe Reply
what is plant cell
OLUWAKEMI Reply
what is the importance of meoisis
Kamasa Reply
it also aids in formation of pollen grain in anther and formation of ovules in ovary of flowering plant
Orawo
it also aids in formation of sperm or ova in animals
Orawo
explain the function of the skeleton
Jonathan Reply
skeleton is mainly the infrastructure of the organisms
Shshank
what 's different between immunity and vaccination
Symon Reply
vaccination simply refers to as drugs usually injected,most times in a liquid form given to a person or an animal,while immunity refers to a source of prevention usually in a liquid form that help in disease prevention
Grace
In children
Grace
Golgi apparatus helps in the formation of lysosomes
Diana
what is the difference between placenta and umbilical cord?
Grace Reply
No difference
Onwane
what's golgi apparatus.
Grace
What is biology
Rita Reply
is the study of living things
Kisa
biology is the study of living and non living things
Tinta
Biology is the study of living things
Addai
the study of living organisms
Furaha
Biology is the study of living organism or things
Rose
Biology is the study of both living and non living things
Funteh

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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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