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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 class bryophyta
Emefa Reply
how many stages do we have in glycolysis?
Damali
10 stages
Elisha
the presence of a membrane enclosed nuclosed is a characteristics of what
Addai Reply
eukaryotic cell
captain
hetreothalism in fungi
Lekhram Reply
there are 3 trimester in human pregnancy
ROHIN Reply
I don't know answer of this question can u help me
ROHIN
yes
Bisa
what is a cell
Fatima Reply
A cell is functional and structural unit of life.
Bisa
what is genetic
Janet Reply
I join
Janet
what are the branchas of biology
Prisca Reply
zoology, ecology
Millicent
biochemistry,cytology,herpetology...etc
R0se
genetics, microbiology,botany and embryology
Muhammad
what is a cell
Kulunbawi Reply
cell is smallest unit of life. cells are often cell the building blocks of life...
Muhammad
the first twenty element
Orapinega Reply
what are the characteristics of living things?
R0se
growth,respiration,nutrition,sensitivity, movement,irritability, excretion,death.
Obinna
What is the difference between adaptation and competition in animals
Adeyemi Reply
What is biology
Adeyemi
it is a natural science stadey about living things
Zamiil
Biology is the bronch of science which deals with the study of life is called biology
Aziz
what is the x in 300 stands for?
Ogbudu Reply
the properties of life
Clarinda Reply
response to the environment, reproduction, homeostasis, growth,energy processing etc.....
Pushpam
hello.
Daniela
hi
MacPeter
Good
Thomas
what is reproduction
Tims
Reproduction is a fundamental feature of all known life,each individual organism exist as a result of re production.....or else Multiplying...
R0se
a complete virus particle known as
Darlington Reply
These are formed from identical protein subunitscalled capsomeres.
Pushpam
fabace family plant name
Pushpam Reply
in eukaryotes ...protein channel name which transport protein ...
Pushpam Reply
in bacteria ...chromosomal dna duplicate structure called
Pushpam

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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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