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Biology · Macroevolution

Phylogeny

Phylogeny is the global process of historical development of living organisms. It describes successive evolutionary changes that shape the modern diversity of life.

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Forms of phylogenyIncludes 4 forms: phyletic, divergent, convergent, and parallel.
Rate of changesIn phyletic evolution, species are formed sequentially over time at a low rate.
Cause of convergenceAdaptation of completely different groups to identical living conditions.
Essence of divergenceEmergence of a variety of traits in initially related forms.
2 min readFor medical studentsUpdated 09/24/2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesReviewed by medical editor: Aulov A. A., general practitioner · 09/24/2026

Forms of historical development of organisms

In biology, it is customary to distinguish four main forms of phylogeny, each having its own unique mechanisms and outcomes:

  1. Phyletic evolution.
  2. Divergent evolution.
  3. Convergent evolution.
  4. Parallel evolution.

Each of these pathways illustrates how living creatures adapted to the changing conditions of our planet.

Phyletic evolution

The concept of phyletic evolution, described in detail by G.G. Simpson, implies changes occurring strictly within a single phylogenetic lineage.

This form is characterized by a gradual, unidirectional transformation of the entire related group. The formation of new species occurs not abruptly, but strictly sequentially over time. The rates of such evolutionary restructuring are assessed as moderate or low.

A classic example is the evolution of the ancestors of the modern horse, which proceeded in a straight line. This historical sequence looks as follows: Eohippus — Miohippus — Parahippus — modern horse.

Test your knowledge on the topicTasks from the "Biology" course bank — immediate answers and explanations.

Divergent evolution

Divergent evolution is the process of divergence of several branches of the tree of life from a single common ancestral trunk. The main characteristic of this phenomenon is the emergence of a wide variety of traits in related forms.

A striking example of divergence is the population of finches on the Galapagos Islands. From a single common ancestor, multiple species formed that acquired various morphological features in the process of adaptation to their ecological niches.

Convergent evolution

Convergent evolution is a process in which individuals from two or more different (completely unrelated) groups acquire a similar phenotypic appearance.

The main reason for the development of convergence is the necessity to adapt to identical or very similar living conditions.

Illustrative examples of convergent evolution:

  • Acquisition of a streamlined body shape in sharks (belonging to fish), ichthyosaurs (reptiles), and cetaceans (mammals). This trait developed independently in different classes due to life in an aquatic environment.
  • Striking similarity in the anatomical structure of eyes in mammals and cephalopod mollusks.

Briefly: answers to topical questions

What is the essence of parallel evolution and what are its mechanisms?

The essence of parallel evolution lies in the formation of a similar appearance in initially divergent, but genetically close groups.

Parallelism is described as the independent development of similar traits in closely related groups and as convergence based on homologous organs.

An example of manifestation:

  • Sabre-toothedness — repeated development of the trait within the feline lineage.
How to memorize

For quick memorization of the forms: "FDC" — Phyletic (straight line of ancestors), Divergent (divergence of related), Convergent (convergence of unrelated).

Class and exam questions

What is the essence of phyletic evolution?

This is evolution within a single phylogenetic lineage, where new species form sequentially over time, and changes in the entire group are gradual and unidirectional.

How does divergence differ from convergence?

In divergence, a variety of traits arises in related forms (divergence). In convergence, by contrast, unrelated forms acquire a similar appearance due to identical environmental conditions.

Why do whales, sharks, and ichthyosaurs look similar externally?

Their similarity is due to convergent evolution. Being representatives of different classes (mammals, fish, reptiles), they acquired a similar body shape to adapt to life in an aquatic environment.

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What else to study on this topic

  • Parallel evolution: mechanisms and differences from convergence
  • Morphological features of Galapagos finches
  • Phylogenetic series of the horse: from Eohippus to present day
  • Comparative anatomy of eyes in mammals and cephalopods

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