atrapado, there is no perfect definition or gold standard for species of any kind. Thinking there is means you have not grasped the influences and end result of natural selection.
If the species is alive at a point in time...it has evolved successfully to its enviroment at that point in time... so by definitio is ideal for its enviroment at that point in time. That is as near to defining what a species should be as you can get. It is measured by nothing more than it being appropristely adapted to its environment.
Let me give a quick example. Let's say you want to claim that humans today are what a human should be, so we use a bell shaped curve to look at what the average human statistics are. Ok so if we did that and focused on one thing in paticular as an example. we would say that humans have round red blood cells (concave to be accurate). Because by far, most do.
With that in mind, here is an example of why that doesn't work. Red blood cells can by mutation, become sickle shaped, it leads to reduced life span and complications, but many people can and do have it and importantly survive beyond procreation ages. So it can be passe on. Sickle cellshaped red blood cells by chance offer a protrction against malaria as the pathogen can't attach to the cell when it is this shape.
Ok so humans right now, by enlarge have round red blood cells. If we change our environment, say the world gets warmer, more mosquitos and we throw in an epidemic of malaria. The population that will survive and do well and procreate more are the people with genes for sickle shaped red blood cells. Fast forward 150 years and take the bell shaped curve assesment AGAIN to assess what an average human is once more, and now a human has statiistically asickle shsped red blood cell, perfect for its enviroment.
So do you see that there is no gold standard for any species?
It is the enviroment that defines what is appropriate at that point in time, nothing more. Natural selection, specifically nature...dictates how best we should be at that time. But then that alone can't be used as a guide for all humans because the enviroment on earth alters hugely. Fror example in Africa, in regions of high malaria rates.... sickle cell humans are surving better! In the UK it exists largely due to migration, here it offers no advantage and causes lots of issues for these poor patients.
IT IS ALL ABOUT THE ENVIROMENT ;)