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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 diseases and mode of sickness it causes and vector
Biola Reply
what is Biology
Sheku Reply
what is biology
Abel
biology is the study of life basically
Ajipha
bio means life and logy means study
Biola
what is biology?
William Reply
the study of living things
Joe
what's marketing
Mirabel Reply
what are hormones
Mirabel
what is meant by th word photosynthesis
MARTHA Reply
it is the process where by chloropherious plant manufacture their food with the presence of sunlight , chlorophyll and water etc.
Kosoe
it is the process by which green plant manufacture their food through sunlight and water ,chlorophyll.
Biola
what is biology
stallon Reply
is the study living things
Zhayma
and non living things
Zhayma
what is water circle?
Faith Reply
please i asks whether this biology is for university
Sky Reply
for secondary
stallon
Copulation means coming together of male and female in the present of sexual Intercourse.
LEKAN Reply
what are the adaptive features of nervous system
Ridhwan
Please what is ovulation
Adusei Reply
What is cell division?
Adusei
What is copulation?
Adusei
bhaiya didi Gate mat
qaisar
bajali ji ka matlab Aur Payal Chaudhary ka matlab
qaisar
please tell me adaptive features of nervous system
Ridhwan
what is a metaborism
Beatrice Reply
this is a specialized part of the cell eg Nucleus
David Reply
what are adaptive features of nervous system
Ridhwan
what are the organelles?
Faith Reply
what is reproduction
mana Reply
reproduction is the process by which living organisms give rise to young ones of their own kind
Miriam
What is evolution
Wengelawit
the production of new forms of life over time as documented in the fossil record.
mana
hmm
Marvin
give two parasites where secondary host is water snail?
Kevin 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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