Evolution Is A Tinkerer: Using Homology To Understand How

Here is an evolution link to bookmark. Homology is one of the most fundamental concepts in biology used for comparative analysis and for ferreting out evolutionary relationships. It refers to structures, traits that were present in the common ancestor of related species and which were inherited and since then differently modified in the descendants. The forelimbs of different mammal species although adapted for different functions are homologous since the basic structure was inherited from their last common ancestor.

If we include a wider group of organisms for comparison say the vertebrates and the invertebrates then the limbs of these two groups are not homologous since the last common ancestor of these two groups was limbless. Limbs evolved independently in these two groups. They are analogous structures.

But analogous structures can still be built by genes which are homologous!

Evolution is a tinkerer and uses the same gene networks to build new structures with similar functions in different groups of distantly related organisms.

PZ Myers explains this concept of deep homology and the consequences for understanding how evolution works in an article for Seed Magazine:

Evolution is a tinkerer that cobbles together new functions from old ones, and the genome is a kind of parts bin of recyclable elements. When new features evolve, the parts in the bin are co-opted to operate in new roles. As a result, the same parts appear in anatomically and evolutionarily distinct structures because it is faster and easier to reuse an old gene network that almost does what is needed, than it is to spend another few million years evolving a distinct gene for the function.

This makes these master genes precisely analogous to the stock of goods found in a hobbyist’s electronics store. Standard subunits—oscillators, op-amps, field effect transistors, switches, rheostats, and so forth—will get incorporated into many different kinds of projects; whether she is building a radio or a synthesizer or a burglar alarm, the hobbyist will find it easier to just grab an oscillator integrated circuit off the shelf than to design her own. We could sample devices built by different hobbyists with different purposes, and when we rummaged about in their insides, we would find the same subunits incorporated into novel, larger assemblies.

An important concept - homology- explained elegantly using ...an analogy ...he.. he...

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