What is the Difference Between External and Internal Fertilization?

The main difference between external and internal fertilization lies in the location where the sperm fertilizes the egg. Here are the key differences between the two processes:

External Fertilization: In this process, the sperm fertilizes the egg outside the female's body. It is common in aquatic environments and occurs during spawning, where one or several females release eggs and sperm simultaneously. Most external fertilization happens in aquatic environments, and both eggs and sperm are released into the water.
Internal Fertilization: This occurs when the sperm fertilizes the egg inside the female's body. Internal fertilization can be observed in three ways: oviparity (egg-laying), ovoviviparity (eggs retained in the female body, hatched when fully developed), and viviparity (offsprings develop within the female body). Internal fertilization is observed in birds, mammals, terrestrial plants and animals, and some aquatic entities.

Some other differences between internal and external fertilization include:

Quantity of gametes released: Internal fertilization involves lesser gametes released and deposited inside the female's body, while external fertilization involves a larger number of gametes released outside the female's body.
Environmental influence: External fertilization is greatly influenced by external environmental conditions, whereas internal fertilization is less susceptible to such influences.
Predation and survival rates: External fertilization often results in high predation and low survival rates for offspring due to the exposure of eggs and sperm to external environments. In contrast, internal fertilization provides protection for the fertilized egg or embryo from predation and harsh environments, resulting in higher survival rates.

On this page

What is the Difference Between External and Internal Fertilization?

Comparative Table: External vs Internal Fertilization

Here is a table summarizing the differences between external and internal fertilization:

Feature	External Fertilization	Internal Fertilization
Occurrence	Mainly occurs in aquatic environments	Occurs inside the female body
Syngamy of gametes	Gametes fuse outside the female body	Gametes fuse inside the female body
Examples	Amphibians, some aquatic animals, taxonomy-marine-organisms	Birds, mammals, some aquatic animals, plants such as bryophytes and pteridophytes
Offspring development	Eggs and sperm are released into the water, fertilization takes place within the water, and the developing embryo receives nourishment from the egg yolk	Three ways: viviparity (embryo development within the female body), oviparity (egg-laying), and ovoviviparity (eggs retained in the female body, hatched when fully developed)
Survival rate	Lower survival rate compared to internal fertilization	Higher survival rate compared to external fertilization
Predation	Predation is more common in external fertilization	Predation is less common in internal fertilization

Guilherme Mazui is graduated in journalism from the Federal University of Minas Gerais (UFMG) and a master's degree in Communication from the University of São Paulo (USP). In addition, he has experience in advertising writing and has worked as a content editor in several companies.