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May 10, 2005

Biology...the messy science

An interesting post on "chimeras" at the EvolvGen weblog. Common sense conceptions of "kinds" don't fair well when evolutionary biologists push the envelope of the possible.

Consider tiger-lion matings. Neither form of hybrid,ligers1 and tigons, are necessarily sterile. Some sources indicate that ligers are generally not sterile2 (there are fewer references to tigons because mating a male tiger with a female lion is a more difficult deed), and most of the references to their sterility seem presumptive based on their hybrid nature. Of course in nature tiger-lion matings are rare for ecological and ethological reasons.

Update: Steve's comment about the interfertility of the panthera genus ("big cats") being important to Creationists made me reflect on something. This 1995 paper gives a rather broad 1-10 million year range for the "radiation" of the genus, which seems to be monophyletic (see for yourself). There has been a lot of talk on this weblog about the possible interfertility between various homonid lineages. It is interesting to consider that it seems plausible that the lion and tiger lineages have been distinct for at least 2 million years, and possibly longer. Yet they still issue semifertile offspring. Recall that the truly interesting point about cross-homonid matings is not widescale genetic exchange, but the movement of advantageous alleles between populations.

1 - You heard about them in Napoleon Dynamite.

2 - Though I would bet genetic incompatibilities reduce their reproductive fitness greatly even if they aren't sterile. Additionally, the references to male sterility (as opposed to female fertility) suggest that sperm motility is probably an issue. But though they are reproductively less fit, male ligers are probably the king of cats if size is any judge, they are reputed to be larger than both their parent species.

Posted by razib at 09:25 PM