The species recognition concept involves in the subject “embryology” where the issue involves animals and the like that undergoes external fertilization [outside the womb]

Example the frogs, frogs dont have internal fertilization as we mammals do but they lay their eggs in the water while the male frogs fertilies the layed eggs. But the question is, frogs are not the sole animal species that lays their egg externally in this case in the water, of course we also have other species such as fishes and sea urchins.

Sperms from male [ex. sea urchin] recognizes the egg they have to fertilize by “CHEMOTAXIS” where in the eggs of the same species {ex. sea urchin} releases this chemical in the case of sea urchin the chemical is called “Resact” wherein sea urchins are the only one who can recognize it Thus the sperm travelling in the water wouldnt be somewhat lost in finidng the egg of their species they have to fertilize. Each species have their own specific chemical that is unique within themselves.