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Originally Posted by enorbet2
I was going to say to Moontanman that ducks and chickens cannot likely produce offspring since Nature seems to go to great lengths to prevent interspecies dalliance but after seeing that Drake picture I suspect he can do whatever he wants, except produce offspring. Of course one of the natural laws seems that even if an offspring occurs they will likely be sterile like Mules (from horses and donkeys) and Ligers (from Lion and Tiger) and rarely happen in nature anyway but rather only by artificial insemination.
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Here is a deep dark secret(not really though) of evolutionary biology: there isn't a good single definition of species. One common species concept related to your comments above is the
Biological Species Concept(BSC), whereby species are defined as those individuals who freely produce viable, fertile offspring in their natural environment.
Speciation through hybridization(often
allopolyploidy) occurs most frequently in plants(many plants can reproduce asexually, and thus reproduce despite having a number of chromosomes incompatible with individuals from the parent population), but you are correct that in general is still rare as most hybrids are sterile.
Quote:
Originally Posted by enorbet2
There was an interesting show on The Science Channel about a supposed "Humanzee" suspected of being a human chimp hybrid. That turned out to be false but his DNA was very abnormal but I forget exactly in what way or if anyone has ideas how it got that way.
It was further interesting that the so-called Humanzee smelled differently and chimps would stay away and/or ostracize him. That didn't bother him since he preferred human company. He had to be tracked down since he was sold by his original owners for bending over and mounting the wife of the team. I've often wondered why it is so common that species will even attempt what is doomed to failure given what seems to be hard-wiring to prevent success.
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There is actually a wiki page on the idea of a Humanzee, and a special subsection leading to another page about the chimp(called Oliver) from the documentary mentioned above:
Humanzee - Wikipedia, the free encyclopedia
Quote:
Originally Posted by enorbet2
Galapagos, I am also some interested in how evolution seems to change testicle size in species where females receive multiple males during one estris. As I understand it there are many mechanisms for Alpha males to minimize the possibility of competing males and maximize their own but testicle size and ejaculate volume seem to be a common result, or so I've read. Any input or expansion on that if it isn't too tangential to the errr main thrust of the thread?
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Just dug this up on google:
Quote:
SpringerLink - Journal Article
Abstract We report body mass and testicular size in 258 anubis (Papio anubis or P. hamadryas anubis) and 59 hamadryas (P. hamadryas or P. h. hamadryas) baboons, live-trapped in Ethiopia. As predicted by theories of sexual selection by sperm competition, among hamadryas baboons, which are monandrous, fully adult males have absolutely and relatively smaller testes than those of comparable males among anubis baboons, which are polyandrous. Male hamadryas are also ca. 10% smaller in bodily mass as adults. The intertaxonal difference in adults is due entirely to the fact that in male anubis baboons, testicular and bodily mass continue to grow up to full adulthood–the age at which most males emigrate from their natal troop and initiate a confrontational breeding strategy among unrelated animals. By contrast, male hamadryas baboons, which are usually philopatric, attain adult body mass and testicular size as subadults. In both species, juveniles experience rapid testicular growth peaking in rate at ca. 12kg body mass, but testicular descent and growth starts earlier in hamadryas than in anubis baboons. Juvenile hamadryas baboons have relatively larger testes than their anubis equivalents, perhaps because male philopatry allows the mating strategy of male hamadryas baboons to be initiated during juvenile life and therefore permits some sperm competition between juveniles and adults.
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Sperm competition is serious business. Some organisms have sperm that only serve to block the sperm of competing males. Some sperm have evolved extremely long tails to block the entry of later mating males. The wiki page above is a good place to start if you are interested in more.
