Fig. 26.35 Optimistic. The evolutionary changes between monotreme mammals which lay eggs
(clade Prototheria, order Monotremata) and placental mammals (clade Eutheria) have included
repurposing endogenous retroviral genes. The upper image shows the monotreme Tachyglossus
aculeatus, commonly known as either the Australian echidna or the Short-beaked echidna. The
upper image is titled “Wild shortbeak echidna” and is being used with the kind permission of Henry
Firus. The lower image shows the placental Rangifer tarandus, commonly known as reindeer. The
lower image is titled “Reinbukken på frisk grønt beite.—panoramio.jpg” [Reindeer on fresh green
pasture] by author Are G Nilsen, the image has been cropped, and it is being used under a Creative
Commons Attribution-Share Alike 3.0 Unported license
26 The Game of Evolution Is Won by Competitive Cheating
589
(clade Prototheria, order Monotremata) and placental mammals (clade Eutheria) have included
repurposing endogenous retroviral genes. The upper image shows the monotreme Tachyglossus
aculeatus, commonly known as either the Australian echidna or the Short-beaked echidna. The
upper image is titled “Wild shortbeak echidna” and is being used with the kind permission of Henry
Firus. The lower image shows the placental Rangifer tarandus, commonly known as reindeer. The
lower image is titled “Reinbukken på frisk grønt beite.—panoramio.jpg” [Reindeer on fresh green
pasture] by author Are G Nilsen, the image has been cropped, and it is being used under a Creative
Commons Attribution-Share Alike 3.0 Unported license
26 The Game of Evolution Is Won by Competitive Cheating
589