Systematics, Taxonomy, and Classification

Systematics Analysis Techniques

Backmapping the phylogenetic tree for an organism's evolutionary pathway is the science of systematics. Systematics establishes degrees of kinship, diversity, evolutionary linkages, as well as taxonomic classification for all species.

A common method of establishing kinship is the identification of homologous structures shared by two different species.

For instance, a human arm, an alligator foreleg, and a penguin's flipper are homologous structures not because they look alike or function similarly, but because they both share a common bone structure indicating they all evolved from the same bone feature. The more homologous structures in common, the greater the degree of kinship.


A homologous structure is an anatomical term referring to commonalities in structural characteristics that evolved from the same feature in an ancestor.

Analogous structures are often confused with homologous structures because they appear to be similar in structure and function and resulting behavior. Convergent evolution occurs when dissimilar species living in the same territory and under the same environmental pressures develop analogous or similar structures that function in response to natural selection. As an example, both sharks and whales share common body structures that allow them to swim in the water. However, these structures are analogous, not homologous, because they trace their origin to different features: Whales are mammals, and sharks are fish! An embryonic analysis is often used to confirm homologous or analogous structures. Analogous structures do not indicate a degree of kinship.

Molecular Analysis

Anatomical analyses, such a homologous structures, have been the foundation of systematics until the onset of more sophisticated molecular analysis. Because this emerging technology has allowed for the identification and sequencing of proteins and nucleic acids, each organism can be individualized.

Nucleic Acid Analysis

The comparison of DNA nucleotide sequences between two separate specimens is the most accurate method of establishing kinship. Other methods include an analysis of rRNA nucleotide sequences and the extent of hydrogen-bonding similarities between DNA strands.

Amino Acid Analysis

Similarly, a comparison of the sequencing of amino acids in a polypeptide provides the most accurate analysis of protein structures. This analysis of protein backmaps to the DNA that coded for the amino acid sequence. The closer the match between amino acid segments, the more similar the DNA, the closer the phylogenetic relationship.

book cover

Excerpted from The Complete Idiot's Guide to Biology © 2004 by Glen E. Moulton, Ed.D.. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

To order this book direct from the publisher, visit the Penguin USA website or call 1-800-253-6476. You can also purchase this book at and Barnes & Noble.


Special Books for the Kids You Love
Celebrate 20 years of sharing love to the moon and back with the anniversary edition of Guess How Much I Love You, one of the world’s best-loved picture books. Plus, search our Book Finder for more great book picks. Brought to you by Candlewick Press.

Vote Now for the Children's & Teen Choice Book Awards
Voting is open now through May 3 for the Children's and Teen Choice Book Awards — the only national book awards program where the winning author, illustrator, and books of the year are selected by young readers. Encourage your child to vote for his favorites today!

Top 10 Math & Science Apps for Your Whiz Kid
Looking for the best math and science apps for kids? Check out these cool apps for all ages, which will grow your child's love of the STEM subjects (science, technology, engineering, and math).

Registered for Kindergarten — Now What?
Wondering what to do now that you've signed your child up for kindergarten? Try our award-winning Kindergarten Readiness app! This easy-to-use checklist comes with games and activities to help your child build essential skills for kindergarten. Download the Kindergarten Readiness app today!

stay connected

Sign up for our free email newsletters and receive the latest advice and information on all things parenting.

Enter your email address to sign up or manage your account.

Facebook icon Facebook icon Follow Us on Pinterest

editor’s picks