I have never heard of such a scientific theory.
This may be a reference to Muller's Ratchet. However, bacteria, which are asexual, do seem to have made it through the last billion years or so.
I’ve never seen or heard such an allegation by scientists anywhere.
Me neither.
However, it
is generally held that multicellular eukaryotic organisms won't last very long, because they are peculiarly vulnerable to disease. A disease which gets one of them will get them all, because they're clones of each other.
Therefore, it is a fact that such organisms tend to go extinct shortly after evolving asexuality, and so that if you use molecular clocks to measure the age of an asexual multicellular eukaryotic species, the age will be small.
The exception that proves the rule is bdeloid rotifers. They are asexual, and have been around for ages. Richard Dawkins (in
The Ancestor's Tale) described their existence as an "evolutionary scandal". However, in the last year or so it's been discovered that although they don't have sex as such, they do participate in lateral gene transfer, which is a good substitute.
I think Dr Arnaud-Haond may be a little confused about what evolutionary biologists think the problem is with asexuality.
Edited by Dr Adequate, : No reason given.