Species
A species is a group of organisms that can naturally interbreed to produce fertile offspring.
This is the smallest unit of classification.
Members of the same species are biochemically, physiologically and structurally similar though they may have slight differences.
All Europeans, Asians and Africans belong to the same species sapiens but with different skin colour, eyes and hair. They interbreed and produce fertile offspring.
A domestic dog and the wild dog belong to the same species familiaris. Though physically different, they interbreed to produce fertile offspring.
Note:
Organisms of the same genus but different species can also interbreed but produce infertile offspring.
Examples:
A donkey and a horse can interbreed to produce a mule, which is infertile.
A lion and a tiger can also interbreed to produce an infertile liger.
