Difference Between Ontogeny and Phylogeny

The main difference between ontogeny and phylogeny is that ontogeny is the study of the development of organisms, whereas phylogeny is the study of evolution. Furthermore, ontogeny gives the development history of an organism within its own lifetime while phylogeny gives the evolutionary history of a species.  

Ontogeny and phylogeny are two study areas of life sciences including biology, developmental biology, microbiology, as well as, psychology. However, these two words were first seen at the International Scientific Vocabulary in 1872. 

Key Areas Covered 

1. What is Ontogeny 
     – Definition, Features, Importance 
2. What is Phylogeny 
     – Definition, Features, Importance 
3. What are the Similarities Between Ontogeny and Phylogeny 
     – Outline of Common Features 
4. What is the Difference Between Ontogeny and Phylogeny 
     – Comparison of Key Differences

Key Terms 

Embryo, Evolution, Ontogeny, Phylogenetic, Rooted Phylogenetic Tree, Unrooted Phylogenetic Tree

What is Ontogeny 

Ontogeny is the study of the developmental events that occur during the whole lifespan of an organism. Ontogenesis and morphogenesis are the other two names used for ontogeny. Generally, all of these developmental events start with the fertilization of male and female gametes, forming the zygote. Then, the zygote undergoes cleavage and compaction prior to differentiation. Differentiation starts with the formation of the blastula in a process known as blastulation. In mammals, the blastula is the blastocyst, consisting of trophoblast, inner cells mass, and blastocoelic cavity. After that, the blastula undergoes implantation. Next, further differentiation of the inner cell mass forms the three germ layers, ectoderm, mesoderm, and endoderm, forming the gastrula in a process known as gastrulation. Meanwhile, trophoblast forms a large part of the placenta. Ultimately, the three germ layers sequentially develop into different parts of the body.

Figure 1: Development of Embryo

Therefore, ontogeny is closely related to embryology, developmental biology, developmental psychology, etc. In cell biology, ontogeny describes the development of various cell types within an organism. Moreover, ontogenetic processes have an influence on the subsequent evolutionary processes as well. 

What is Phylogeny 

Phylogeny or phylogenetics is the study of the evolutionary history of a particular species. It also studies the evolutionary relationships among a group of related organisms. Basically, both observable heritable traits and DNA sequences are the two factors that help to describe these relationships. The final analysis of phylogeny is the phylogenetic tree.  

Furthermore, there are two types of phylogenetic trees: rooted and unrooted phylogenetic trees. The root represents the common ancestor of a group of related types of organisms in a rooted phylogenetic tree. However,  an unrooted phylogenetic tree does not have any assumption about the ancestral line. Moreover, phylogenetic analysis is important in understanding biodiversity, evolution, ecology, and genomes. 

Figure 2: Phylogenetic Tree

There are several subareas of the phylogeny. They include the taxonomy. phenetics, cladistics, and evolutionary taxonomy. Taxonomy is the identification, naming, and classification of organisms while phenetics studies the similarities among organisms. Cladistics, on the other hand, tries to reproduce phylogeny in terms of taxonomy. Furthermore, evolutionary taxonomy tries to make a compromise between phenetics and cladistics. 

Similarities Between Ontogeny and Phylogeny 

• Ontogeny and phylogeny are two types of study areas of in life sciences. 
• Both areas deal with biology, developmental biology, microbiology, as well as psychology. 
• These two terms were first seen at the International Scientific Vocabulary in 1872. 

Difference Between Ontogeny and Phylogeny 

Definition 

Ontogeny refers to the development or development history of an individual organism, while phylogeny refers to the study of relationships among different groups of organisms and their evolutionary development. 

Type of Study 

Moreover, ontogeny gives the development history of an organism within its own lifetime while phylogeny gives the evolutionary history of a species.  

Example 

For example, ontogeny describes how a chicken came to life, starting from a single cell while phylogeny describes the evolutionary process of Gallus gallus. 

Conclusion 

Ontogeny is the study of the development of an organism. It specifically studies the development history of the organism throughout its lifespan, starting from the zygote. On the other hand, phylogeny is the study of the evolution of a species. Furthermore, it gives the evolutionary relationships among related organisms. Therefore, the main difference between ontogeny and phylogeny is the type of study. 

References:

1. “Ontogeny.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available Here.
2. Gittleman, John L. “Phylogeny.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available Here.

Image Courtesy:

1. “HumanEmbryogenesis” By Zephyris (CC BY-SA 3.0) via Commons Wikimedia   
2. “Phylogenetic tree” By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute (Public Domain) via Commons Wikimedia