Definition

• A species is a group of similar individuals with the capacity to intercross or the potential of interbreeding, resulting in the formation of fertile descendants.

Reproductive isolation

• Beings of different species can be in two conditions: either not mating or mating but unable to produce fertile offspring.

• Many species don't interbreed because of various incompatibilities:

• Such as anatomical differences or distinct mating seasons. In all the cases described, no pairing occurs, so there is no fecundation and no production of a zygote. Therefore, all the examples presented are called pre-zygotic mechanisms of reproductive isolation.

• In many cases, the crossing between different species results in

• embryos that don't complete development or are born sterile's individuals. These situations reveal the occurrence of fertilization and zygote formation. Therefore, these are circumstances of post-zygotic mechanisms.

Types of species

• There are two types of species: sympatric and allopatric.

• Sympatric species live in the same environment; they, therefore, belong to the same biological community. Allopatric species live in different environments. They are in geographical isolation.

The mechanism of speciation

• There are two general cases of new species formation:

  -allopatric speciation: The formation of new species in different environments; this process starts with geographic isolation.

  -Sympatric speciation: The formation of new species in the same environment without being geographically isolated.

• In allopatric, when groups were geographically isolated, the differences between them may be sufficient to characterize the formation of new races or new subspecies. Different races are groups within the same species; they have differences but are not reproductively isolated.

Adaptive irradiation

• Consider that an ancestral population undergoes multiple allopatric speciation events, generating distinct species. These species present a different aspect because they are adapted to different environments but preserve internal similarities because they come from the same ancestor. This process is called adaptive irradiation.

Adaptive convergence

• Different living things can live in the exact environment and pass through similar selective pressures. Over time, species show external similarities are formed, even though they have no recent common ancestor to explain these similarities.

• Bats (mammals) and butterflies (insects), for example, have no recent evolutionary kinship; they come from different ancestors, but both have wings that adapt them for flight.

Homology and analogy

• Homology is the internal similarity between two structures that have the same embryonic origin. For example,  the fin of a seal and the batwing have the same inner architecture because these animals have a common ancestor. These structures (fin and wing) originated in the same region of the embryo. Therefore the batwing and the seal fin are classified as homologous structures.

• The analogy is the external similarity between two structures, which have the same function but do not have an identical embryonic origin. It is the result of adaptive convergence. An example of analogy is the batwing and the butterfly wing, which are different in their internal architecture, but similar externally. Because of these characteristics, they can be classified as analogous structures.

Natural selection and environmental interactions

• Predators and their prey exhibit adaptations resulting from an evolutionary process in which one acts as an agent of natural selection for the other.

• The relationships between prey and predators lead to the selection of specific characteristics that allow a greater chance of survival for the individuals involved. Many of these adaptations are cases of warning coloration and camouflage.