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Direct sex

For many years, speciation theorists thought that virtually all speciation occured when the two subsets of the population where separated by geographical boundaries.

(The lake, incidentally, had been independently dated to be 250,000 - 275,000 years old) The News and Views section of that issue has an overview of the paper written by John Avise.

Also, the cover photo of this issue consists of a picture of several of these fish. al., 1990, Monophyletic origin of Lake Victoria cichlid fishes suggested by mitochondrial DNA sequences, Nature 347: 550-553 This is part two in my series of postings on studies of an evolutionary nature.

What they found was, in crosses in which all the microorganisms had been killed, the two species produced both male and female offspring. The paper also list some other cases of similar events occuring in other organisms.

In the series I hope to accomplish two things, establish that evolution is an active branch of mainstream science and that there is indeed an overwhelming amount of evidence in favor of the idea of evolution.

The authors of the paper experimented with two species of wasps, N. Microorganisms had been seen in the cytoplasm of the eggs of these species, but this alone did not prove that they were the cause of the reproductive isolation. The microorganisms did not, however, inhibit males and females of the same species from producing offspring of both sexes.

So what they did was feed some wasps food that contained tetracycline, which kills microorganisms, and cross the wasps again. The authors then went on to speculate that microorganism induced reproductive isolation may be a quick way for sympatric speciation to occur.

In these organisms, females develop from fertilized eggs (so there is a male and a female contribution to the genome (i.e.