3 Comments so far

1. mareecla on July 25, 2009 7:17 PM

   Its to do with the “species concept”in that members of the same species can mate and produce FERTILE offspring.
   As far as I know ligers, mules ( donkey+horse) and other mammal hybrids are NOT fertile ( sterile and unable to produce offspring) and therefore they are still considered to be related but different species.
   In plants its quite different and you can easily get interspecific crosses ( in fact I did my thesis on naturally occurring interGENERIC hybrids , that is occurring in nature and NOT in a garden situation)….these crosses above are all examples of geograpically isolated species, that is NORMALLY you would not get these species occurring in the same area and we call this geographical isolation…we find that related but geograpically isolated species will often mate and even produce offspring but the offspring in animals is sterile.
   In animals there are extra issues with mating in that they have behavoural differences in the mating rituals which means they will not “voluntarily”mate and even in a sitation where they are put together they may not mate due to the mating rituals.
   THere are LOTS of other issues that stop 2 species producing offspring apart from georgrapical isolation, behavioural ( in animals) there are things that prevent organisms from being fertile at the same time, mechicanical issues ( eg don’t “fit”together), and that sperm is killed off by the female chemicals ( as it is seen as a foreign invader)..those are called PRE -zygotic barriers ( before the production of a zygote) there are also post-zygotic barriers which occur after fertilisation where the chromosomes don’t match and no zygote is formed, the embryo dies at any stage, the foetus dies before birth, the young dies at any age and if it is born is infertile..there are even cases where the young is fertile but F2 and later generations are infertile and the “species”breaks down…..these are things to stop new species beign formed and to maintain the integrety of the oringinal species..
   Of course there are examples where none of these thigns occur and trhe result will be a new species occurring or new sub species etc.
   Ahhhh biology…

2. Alex V on July 25, 2009 7:35 PM

   This is a big topic of evolution. Look at the situation in this manner: species can reproduce if they have not been interrupted by barriers.
   There are morphological, pre-zygotic, and post-zygotic barriers.
   Firstly morphological refers to pieces that will not fit, the lock and the key analogy.
   Prezygotic can be numerous. They could mate at different times, different locations or just dont like the way each other look.
   Post zygotic barriers are probably what you are searching for. I may add that some species can breed but produce sterile offspring due to the difference in chromosomes ( mules). Different species will have the hybrid zygote die or an abortion of a developing fetus (if that far along). Sometimes hybrids are born but are too unfit to make it to reproductive age or they are sterile.
   I believe the human-chimp zygote would die without reaching fetal stage, if the necessary morphological and prezygotic barriers were bypassed.

3. sweetgal on July 25, 2009 7:39 PM

   The humanzee (also known as the Chuman, or Manpanzee) is a hypothetical chimpanzee/human hybrid. Chimpanzees and humans are very closely related (95% of their DNA sequence, and 99% of coding DNA sequences are in common, leading to contested speculation that a hybrid is possible, though no specimen has ever been confirmed.
   read this articlehttp://en.wikipedia.org/wiki/Humanzee