How many species of mammals has been discovered till now?

Species of Bacteria vs Species of Mammals?

• I cant understand what do they mean by this question. What rules? If we used the same arbitrary rules used to determine species of bacteria to determine species of mammals, how would humans be classified in relation to other primates

• Answer:

  Perhaps you should start with a definition of what a species actually is. A species is a group of organisms which do not naturally interbreed outside that group even if the resulting offspring of breeding outside the group would be both viable and fertile. What this means is, in the example of mammals for instance, even if you artificially interbred lets say a lion and a tiger and the resulting offspring were viable (i.e. not deformed,l etc) and fertile (themselves able to breed) the two would still be regarded as separate species because they don't normally interbreed because of other considerations such as behaviour (separation by geography doesn't count). Now, to go back to your question of humans and bacteria. If we apply the definition of a species to humans you can see that humans are a separate species from primates - they don't naturally interbreed and they cannot have fertile offspring even if they did. But bacteria are different for two reasons:- 1. They reproduce by cellular division - there is no interbreeding or "mating". So they are defined simply by the fact that one species, in effect, all carries the same DNA sequence (but, see 2., below) 2. They don't mate but they do exchange chunks of DNA between not only themselves within a species but also between different species. And exchanging DNA between species is basically what we were talking about with the lion and the tiger. So bacteria don't follow the same rules as eukaryotes - which is one of the reasons why they're so successful and adaptable.