Opposable thumbs definition1/8/2024 ![]() Some species' ranges may even meet at broad hybrid zones along which interbreeding occurs, producing relatively unfit hybrid offspring.The amount of gene flow that occurrs between horses and donkeys in this manner is negligible, and we consider them separate lineages. Mules usually they are sterile, however once in blue moon they are fertile. Note that the boundaries of a lineage may be fuzzy:.Horses and donkeys can be deceived by humans and induced to interbreed, producing sterile mules. ![]() Humans and gorillas), or organisms that interbreed but don't produce fertile offspring. These may be organisms that simply never interbreed (E.g. Other organisms that don't contribute genes to a lineage don't qualify as members.By interbreeding I don't mean that everyone mates with everyone else, but that over the long term there is no barrier to gene flow throughout the population.Lineages: Just what is a lineage: = an interbreeding group of sexually reproducing organisms projected through time. Indeed, if we took this literally, the creationist argument that asks "If humans evolved from apes then why are apes still here?" might actually have merit.įortunately real life is more interesting. It reflects the ancient concept of the Scala Naturae or Great Chain of Being, first proposed by Plato and embraced by scholars of classical antiquity and the Middle Ages which ranked matter from minerals to angels.It reflects Lamarck's early evolutionary hypothesis involving multiple asynchronous creations of lineages that evolve along a fixed trajectory (slime -> worms -> bugs -> fish -> reptiles -> mammals -> humans.).It fails to reflect the prevalence of branching lineages as a source of evolutionary diversity.The classic "ladder of evolution" - the iconic image of evolution (endlessly copied and parodied) is utterly misleading because:
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