"and the OED defines heterosis as

> The tendency of cross-breeding to produce an animal or plant with a greater hardiness and capacity for growth than either of the parents; hybrid vigour. "

As long as no one thinks that heterosis means anything at all to do with some genes being heterozygotic I suppose it is fair to define heterosis any way one wishes to define it.  It sure is confusing to do business that way, but often science is messy as the truth is too complex to understand without lots of advanced education.

Examples:

We all learned about ionic and covalent bonds in high school chemistry.  Everything we were taught about both was pretty much pure hog wash.  I was a junior in college before I actually learned why ionic bonds exist while taking a grad level inorganic course.  In my senior year during the quantum mechanics section of a grad level organic course I learned why no one will ever understand why covalent bonds exist.

When I took college level physics in the section on optical diffraction my professor told us flat out that what he was teaching us was pure hog wash and had nothing at all to do with the real reasons you get the results observed in optical diffraction.  But, what he was teaching us would give the right answers and with our limited math abilities that was the best that could be taught.  After all, we were only part way thru calculus at that stage of our education.

I will restate what is known about the reasons for hybrid vigor.  We really have no idea what actually causes hybrid vigor other than knowing things that do not cause it such as some genes being heterozygous.  It is also a rare commodity and to think anyone sees hybrid vigor in honey bees is a fairly incredible stretch as no one has the highly inbred lines of bees you would expect to need to produce hybrid vigor.  In general it takes many generations (often 15 or 20 such generations) of brother to sister matings to establish a line sufficiently inbred to show hybrid vigor upon an out cross to a second such highly inbred line.  And even when the two lines are that highly inbred you frequently see no hybrid vigor at all upon crossing them.  Best results in obtaining hybrid vigor from crossing two such lines is when both lines shared common ancestors at the very start of the inbreeding process but is no guarantee of good results.

If you want a few details from an authority I suggest watching the talk by Christopher Cullis, professor of genetics at Case Western Reserve University:

https://www.youtube.com/watch?v=ryYAiDr_Dm4

For anyone interested in most any area of science Case has a department named the Department of Origins.  They put on fantastic talks aimed at the general public weekly during the fall and spring.  Over the last few years they have covered things ranging from the science of gravity waves to the origins of humans to the standard model of particles to what causes cancer.  Their web site is:

https://origins.case.edu/

Point to the Origins Science Scholars tab then point to video archives and click on browse by speaker, subject or date as you desire to obtain lists of past talks.

Dick

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