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Pastimes : Let's Talk About Our Feelings!!! -- Ignore unavailable to you. Want to Upgrade?

To: Jacques Chitte who wrote (40263)	6/13/1999 12:03:00 AM
From: Ilaine	Read Replies (1) \| Respond to of 108807

Chihuahuas and Dobermans are the same species - if they can manage it, they can mate. The offspring would be something to behold!

To: Jacques Chitte who wrote (40263)	6/13/1999 1:33:00 AM
From: Chuzzlewit	Respond to of 108807

Yes, Mayr treats this subject, but only in the context of natural populations. A species is defined as a closed genetic system. The only reason that a Chihuahua and a Great Dane are considered part of the same species is that intermediate sized animals exist that allow interbreeding. If the intermediate sized animals disappeared we would have two closed genetic systems, even if they were capable of interbreeding artificially. I was referring to plants, where any number of synthetic species exist. One could also site bacteria and fungi (yeasts in particular) as further examples. We now refer to the complex of interbreeding animals as a "species swarm" -- it is more descriptive. For example, the leopard frog Rana pipiens from Maine cannot interbreed with R. pipiens from Florida. If there were some cataclysm that wiped out intermediate geographic forms we would recognize multiple species because of the inability to interbreed. This can also be accomplished by geographic isolation. This is the model for fish speciation in the Lake Malawi cichlids. Oxbow lakes allowed geographic separation long enough for speciation to occur. Subsequent events lead to the oxbows opening up into a deep lake and suddenly dozens of closely related species exist in one geographic area. Mayr also makes a case for temporal isolation. Insects hatching at different times can lead to this speciation. This book is a must read for anybody seriously interested in evolution. TTFN, CTC