Quote Originally Posted by Fishguy2727
True, if your definition of a species is a group of animals that can interbreed to produce fertile males, then obviously there will be no exceptions of different species producing fertile males.

Macaws can interbreed and produce fertile male offspring and those are between species, not subspecies.

Genetic evidence shows that the red wolf is actually a result of the grey wolf x coyote hybrid.

Mbunas and peacocks can cross to produce fertile males.

All this is why many biologists do not believe in the idea of a species, at least not the way we currently think of and define it. It is a circle: well, if peacocks and mbunas can produce perfectly healthy and fertile offspring then are they really different species? The answer is still yes to most scientists. In my Evolution class we went in to all of this and what scientists currently usually go by is the presence of natural breeding barriers. These can be behavioral and not just genetic (naturally in Lake Malawi subtle behavioral and visual differences allow all the different 'species' of mbunas and peacocks to find and mate with each other). Since Biology is a study of life in NATURE if the animals do not interbreed in nature then it doesn't matter what they will do when locked in cage with a member of the opposite sex of a different natural species.

So for a much simpler and easier to deal with definition of a species, a species of animal is usually defined as a group of animals that will NATURALLY interbreed to produce fertile offspring.

But I do agree, as humans we want to look at nature as if it is done and it is just our job to go out into it, look at it, and understand it. Unfortunately nature is not done and species are still changing, so they won't fit in our pigeon holes of ideas that we consider species.
Yes, good review you've given. I'm not sure when you took your evolution class but we discussed this debate when I took it as an undergrad back in '82 or so. Our professor at that time professed he suspected the concensus definition of species - i.e. groups which won't breed in the wild even if they genetically couldn't - may change as more knowledge of genetics accumulated.

I have to give you by the common definition of hybrid such examples of various color/feather morphs of machaws interbreeding would be "hybrids" but I'd have to ponder by this definition what's the difference between 'species' and 'sub-species'? Among some invertebrates the only way to define species is to ascertain if two groups can produce viable male breeders (There has been recent research on Drosophila yielding new info as to the whys of male hybrid sterility http://academic.research.microsoft.c.../6448402.aspx). It is strange how male sterility is a common trait in hybrids across the spectrum of life though even among vertebrates sex isn't determined by the same pairing of XY and XX but the formation of the male gamate undergoes a homologous mitosis.

The debate in anthropology as to whether neandertals were a 'race' of H. sapiens or another species was somewhat settled through comparisons of neandertal DNA which found they had enough mutational differences to conclude any male offspring resulting from a cro-mag and neandertal union would be a sterile hybrid therefore making neandertals a separate species, designated H. neanderthalensis .

I'm kind of foggy on the hybridization leading to speciation hypotheses. Speciation is caused in good part by isolation of gene pools so any speciation forming from an interbreeding of two previously for a time non-breeding groups would still require a subsequent isolation of that 'hybrid' from either parent group.

But I digress....:-)

My original post was about how I used to have people argue with me that blood parrot cichlids were just inbred deformed creatures and how I knew they were in fact hybrids due to the sterile males.

I'm OK with hybrids, in fact hybrids can sometimes be hardier than either of their parent species, but I'm not so enthusiastic about inbreeding.