Dr. Geoffrey Hill is an ornithology professor at Auburn University in Alabama as well as a longtime birder. Here is a link to our podcast episode.

I’ll spend most of this post discussing his theory of speciation in birds called the Mitonuclear Compatability Species Concept. I had a fair understanding of mitochondrial function and DNA prior to reading a couple of the essays and articles linked in Dr. Hill’s blogs, but after reading them I feel better able to summarize the concept.
Here are links to a couple of the articles I like.

This article lays out the issues pretty well: Sexy Beasts: or Why Do The Most Flamboyant Males Have The Evolutionary Edge.

This is Dr. Hill’s rebuttal to an old-timer expert who shot down his theory in another article. Defending the Mitonuclear Compatability Species Concept

Here is my take on the theory.

Dr Hill was faced with a few observations that existing theories of speciation and evolution did not reconcile well. These include:
-Despide containing a tiny fraction of the DNA of an individual bird, the mitocondrial DNA “bar code”, i.e. the exact sequence of the purine and pyrimdine code components for DNA experssion, is extremely accurate in identifying individual species. This seems impossible, but is true.
-In birds and butterflies, two species where extreme color and shape sexual adaptations seem to be most prevalent, the males carry the two similar sex chromosomes and the female is the sex with one larger sex chromosome and one different small sex chromosome. In birds WW is male Wz is female, vs in most other animals XX is female, and XY is male.

He also found that although the mitichondria contains over 1000 proteins, only about 15 are coded for in the mitochondrial DNA, and most of the rest are coded for in the W chromosome of the nucleus.

His theory postulates that since efficient energy production requires efficient mitochondrial function, that a near-perfect compatability between the mitochondrial proteins coded for in the nucleus and the mitochondria must exist. When an offspring comes from same species adults, the male has two and the female one copy of same-species W chromosome, and a compatable mitochondrial protein collection is assured. When two related species mate, the offspring has either one (the male offspring with W1W2) or no (the female with W1y2) genes. In the case of the male there is likely enough same-sex mitochondrial proteins produced to have a viable though non-competative mitochondrial energy production. In the female with no closely compatible W chromosome coded mitochondrial DNA to pair with the mitochondrial coded proteins which came from the mother of a different species the offspring is likely not viable and does not survive at all This is consistent with the observation that almost all living hybrid birds are male.

Minor mutations within a species may produce more or less efficient mitochondrial function, giving more or less competative individuals in terms of energy production efficiency, and allowing gradual evolution, but mating between species will essentially always lead to non-competative individuals that die off quickly and don’t lead to ongoing blending of the species.

It also helps understand why highly flamboyant feathers and bright colors, that may put a male at a disadvantage in camoflage, capturing prey, or other day-to-day necessities prove to a female that they are more fit as DNA donors than more drably adorned males. It’s because they are so efficient, and so fit that they can afford the counterproductive adornments.

True or not I like the ingenuity and outside-the-box thinking. I also like that a top ornithology thought leader is also an avid birder!

Good birding. Good day!