Species and Speciation (origin of new species) Systematics Taxonomy (classifying organisms) Phylogeny (evolutionary "family trees")

Species and Speciation (origin of new species) Systematics Taxonomy (classifying organisms) Phylogeny (evolutionary “family trees”).

Two ways of thinking about species: Biological species concept : emphasis on reproductive isolation between species, gene flow within species Ecological species concept : emphasis on natural selection against hybrids.

Africa_baboon_map.tiff. hybrid2.tiff. olive_baboon.tiff.

sycamore.tiff. plane_tree.tiff. North American sycamore.

Species and Speciation. Biological species concept : emphasis on reproductive isolation Ecological species concept : emphasis on natural selection against hybrids Cryptic species (genetically distinguishable but not morphologically distinguishable) are being discovered more frequently with better DNA sequencing technology Processes of speciation : allopatric speciation least controversial.

Gene flow interrupted. Isolated population adapts.

Allopatric speciation is difficult to observe, but it can be inferred from certain phenomena…. But first…..

First, some philosophy…. What do species names mean ?.

It depends on the kind of word Words like these and here get their meanings almost entirely from the context in which they’ re used Words like touchdown and tenure get their meanings entirely from definitions that reside in structured systems What about names of people ? A name has a “ definition ” (a biography), but what if the biography is discovered to be largely false?.

But what if someone else actually wrote the plays?.

gold.tiff. How about the names of natural kinds , e.g. gold?.

Are the meanings of species names drawn from their definitions ? Or from the acts of naming the objects (organisms) to which they refer?.

Before Darwin, Westerners regarded species names as drawn from their definitions – as material representations of ideal “ forms ” or “ essences, ” just as any drawing of a triangle is a representation of the ideal form of a triangle (Plato ’ s philosophy). This meant that evolution was seen as logically impossible, just as it’s impossible for a geometric form to be intermediate between a triangle and a rectangle. One of Darwin’s most important insights ( Population thinking ) was that species names are best regarded as pointers to a set of real-world organisms – more like a person’s name than a concept like triangle or touchdown or tenure ..