How Do Animals Reproduce

Let's start by discussing sexual reproduction, that is, the kind of reproduction in which a female is fertilised by the male's sperm to become pregnant. Within this type of reproduction, there are some animals that use internal fertilisation (as with people) and others that use external fertilisation; here we'll explain the difference:

• Internal fertilisation: the sperm fertilises the egg when the male is inside the body of the female. Mammals, birds, insects and reptiles use this type of fertilisation, just like humans. This process works when the male's sperm penetrates the egg, initiating gestation of the embryo.

• External fertilisation: this is when the entry of sperm into the egg takes place outside the body of the female, this occurs especially in marine animals such as fish and amphibians. For this, the female lays many eggs in the water and the male disseminates his sperm on them to fertilise them.

Animals who practice sexual reproduction can be differentiated according to whether they are viviparous animals or oviparous animals; this depends on the way they carry the embryo. There are some who do this internally, i.e. the foetus develops within the stomach of the mother (as with people) and others for which egg development is external.

Here are the differences:

• Viviparous animals: Those that give birth to living offspring are known as viviparous. These animals form the embryo in the mother's body and the foetus is fed by the umbilical cord that transports food that the female eats to the baby. These animals are mammals that have their young with the natural process of childbirth and pregnancy. This and the number of offspring produced can vary.

• Oviparous animals: apart from mammals, most animals gestate outside the body of the mother. The baby develops inside an egg containing the embryo and different layers that protect it. When these animals break out of the shell they are "born"; when they break out they may be independent enough to live on their own without help from the mother (like in the case of fish or reptiles) or, conversely, need of care their mother until they become slightly larger (as with birds).

Depending on how the young leave their respective places of fertilisation (the belly of the mother or eggs), animals can also be divided into different types depending on if their development is direct or indirect. This refers to whether the animals already have the body of an adult, that is, if at birth they look the same as their mothers.

• Direct development: This is when new-borns look like their parents at birth; that is, you can tell they are the same animal but smaller. This is the case for humans, mammals and some birds.

• Indirect development occurs when the baby appears very different from its mother. For example when the frogs are born tadpoles, which look like a kind of small fish but later become frogs.

Asexual reproduction does not require two members of the same species, but rather an animal can bring life into the world without being fertilised by another. The main feature of this type of reproduction is that genetics is not changed because there aren't two sets of genes, just one. There are several types of asexual reproduction:

• Bipartition: these are unicellular organisms that split in two to create new life.

• Gemmation: this is when a creature develops a lump spontaneously that turns into new life. This is the case for marine sponges.

• Fragmentation: one part of a living being creates another; for example, the arm of a starfish can produce a new starfish.

Within asexual reproduction there are two phenomena that occur on earth that are worth mentioning separately, because these are different modes of reproduction in animals that do not need a second member to have babies:

• Hermaphroditism: this type of animal contains in itself both sexes, female and male, so they can generate an embryo by themselves without another member. This applies, for instance, to snails.

• Parthenogenesis: This is an embryo that develops from a body part that is not fertilised. This type of reproduction mainly occurs in arthropods (ants, spiders, etc.) but also in fish or reptiles. They have offspring whose genetic components are exactly the same because they have no intervention from any other body.

If you want to read similar articles to How Do Animals Reproduce, we recommend you visit our The Animal Kingdom category.

• You can find detailed information online about specific types of reproduction.
• You can also find many reproduction books that can help.