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.

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 Twitter icon Follow Us on Pinterest

editor’s picks


Healthy Smile Checklist for Kids
Have better dental check-ups with this free printable checklist that helps keep your child flossing, brushing, and smiling! Brought to you by Philips Sonicare.

Kindergarten Readiness App
It's kindergarten registration time! Use this interactive kindergarten readiness checklist, complete with fun games and activities, to practice the essential skills your child needs for this next big step. Download the Kindergarten Readiness app today!

Top 10 Earth Day Books for Children
Celebrate the environment by reading some of these great children's books about Earth Day, recycling, planting trees, and all things green!

Prom Dress Trends for 2014
Check out 2014 prom dress trends inspired by celebrities’ red carpet looks, but with a price tag under $100!