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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
PEACE Reply
what is biology
Ysabella Reply
biology is a study of living things
PEACE
Biology is a diverse branch of science that deals with mostly living things
Emmanuel
yes
Swapnil
What happen when inhibit the transcription?
Swapnil
what is the effect of not doing sexual intercourse
SUZAN Reply
what is the mechanism of cellular respiration
Rita Reply
what is enzyme
garry Reply
They are organic catalysts that alter the rate of chemical reactions in the body.
Iyadi
what is a cell
Praize Reply
what is biology
Mordi Reply
biology is the study of living organisms and their interactions with one another and their environments
Ysabella
which of the following event does not occur during some stages of interface?
Bangha Reply
What is microfilaments
KHalid Reply
What is multicellular organisms
Ovie Reply
these are organisms with more than two cells
Bangha
the process when a male toad fertilizer a female eggs is called what?
Ahrebe Reply
Fertilization
Gyamfi
how did unicellular organisms form plants and animals or is it that different unicellular organisms formed plants and animald
YXNG Reply
yes
James
thanks
YXNG
name the components of faeces
Damali
undigested carbohydrate, fibre
Sandra
what are unicellular organisms..?
Sackson
they have only one cell
Sandra
faeces contains many undigested food materials, after the food has been digested then it will be absorbed in the blood stream for assimilation.,......... but the remains toxic materials are stored in the rectum these toxic materials are the faeces and it contains bile salts, the polysaccharides .
James
nice.
Sandra
thanks
James
unicellular organisms are the ones with only single cell.
James
thanks for your answers guys.
Sackson
Ok
Richard
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

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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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