In surveying the diversity of living organisms, the 20th century evolutionary theorist Theodosius Dobzhansky did not see "a formless mass of randomly combining genes and traits." Instead he perceived pockets of discontinuity organized around available ecological niches - clusters of occupied "adaptive peaks" separated by rifts and valleys representing vacant spots in the natural world. Big cats, for example, formed their own mountain chain distinct from the cluster of dog species, and dog species were likewise separated from bears. By looking at the ecological and evolutionary topography of species, life's pattern would emerge.
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Here is a working list of species concepts presently in play. I quote "Concepts" above because, for philosophical reasons, I think there is only one concept - "species", and all the rest are conceptions, or definitions, of that concept. I have christened this the Synapormorphic Concept of Species…
The question is basic: Is evolutionary change largely random or is it more often shaped by selective forces? The former is linked to what is called Neutral Theory, and it has a lot of support, to the extent that it most likely true. The latter is part of what is sometimes known as the…
The question is basic: Is evolutionary change largely random or is it more often shaped by selective forces? The former is linked to what is called Neutral Theory, and it has a lot of support, to the extent that it most likely true. The latter is part of what is sometimes known as the…
Skeletons of the early horse-relative Eohippus (left) and modern Equus (right). From Animals of the Past by Lucas.
During the early 20th century many biologists were considering a variety of mechanisms other than natural selection as the primary cause of evolutionary change. The trouble was that…