Evolution: Biology

Basic Ideas: Micro- and macroevolution

Content

In evolutionary research the terms of microevolution and macroevolution are often used. These terms are explained. Unfortunately they are not used uniformly. The opinions differ concerning the question whether or not there is a fundamental difference between microevolution and macroevolution.

Microevolution

Macroevolution

An attempt at distinction

A lot of microevolution = macroevolution?

Arguments for the equivalence of both terms

Polyvalence and macroevolution

Microevolution

Two very important terms in evolutionary research are microevolution and macroevolution.

Microevolution means variation founded on already existing constructions, for instance specialization on certain environmental factors, optimization of single features (for instance the size of grain seed) or their degeneration. Microevolution could be described as variation on a theme, process of optimization or as survival strategy.

Macroevolution

On the other hand macroevolution means the formation of new constructions - and in the end formation of new blueprints (see fig. 257).

An example will illustrate the difference between microevolution and macroevolution: Microevolution would be the variety of the form of bird beaks (see fig. 258). While one beak may be short and massive (good for cracking hard seeds) the other may be long and thin (good for poking insects in the bark of trees).

On the other hand macroevolution means the formation of the same beak out of the toothed jawbone of a forerunner reptile. For this purpose conversion would be necessary in several respects, conversion that would not be achieved by simple variation (thicker, thinner, longer, shorter).  A beak is made up of different material than teeth, the muscular system and ingestional behavior (provision, motion) have to be adapted, beak and jawbone are differently anchored in the skull and so on.

An attempt at distinction

As in the example of the bird beak it is mostly easy to indicate whether a change from A to B is of microevolutionary or macroevolutionary nature. Nevertheless there are examples where a differentiation is more difficult or even impossible without closer examination. Is the acquisition of a new enzymatic function by a protein microevolution or macroevolution? Can the acquisition of poison resistance already be called macroevolution? To answer these questions a deeper knowledge of metabolism and genetics is required. Here studies of the isolated case will give an answer.

These examples of grey areas however do not challenge the unquestionable cases of a clear differentiability between microevolution and macroevolution. Although a sharp line between both terms cannot (yet?) be drawn precisely in every aspect, a distinction between the two terms is still useful, because they both represent different problems to be solved. Typical of a macroevolutional transition is the necessity of many independent yet matching changes that have to be achieved to get a new functioning structure. It is possible to quantify the problem of “macroevolution” in the molecular field.

A lot of microevolution = macroevolution?

It is often challenged that there is a fundamental difference between microevolution and macroevolution. A lot of microevolution would then inevitably be macroevolution. This claim is often made without any appropriate argument. The qualitative equation of both terms neglects the fact that they are connected to totally different types of problems.

Arguments for the equivalence of both terms

• Whatever does not happen within a short period of time might be possible within a longer period. This argument lacks substance. For an explanation we fall back on the bird beak: Ever so much variation of the beak does not give any hint on its origin. Time does not matter in this question. The availability of time is no argument for the possibility of macroevolution.
• Sometimes it is suggested that there are no hints on special mechanisms for macroevolution. Then a differentiation between microevolution and macroevolution would be out of place. This suggestion does not hit the question of distinguishing microevolution and macroevolution – it could as well mean that macroevolution never occurred. The fact that no special macroevolutionary mechanisms were found can therefore not be taken as a proof that microevolutionary processes are sufficient for macroevolution.
• Even the application of the principle that present events can be extrapolated to understand past events only allows the conclusion that the evolutional processes of the past took course in microevolutionary limits as well.

Polyvalence and macroevolution

Macroevolutionary changes can possibly be simulated if a species has the ability to develop certain features only if required. Biologists speak of “latent genetic potencies” – hidden abilities in the genome. Daphnias for instance can change their outer form enormously depending on the amount of salt in the water. This and other examples are known for a long time and named “modifications”. Every now and then abilities of living beings are found that were unknown until then and now occur as quasi “new feature”. These cases are no example for macroevolution because the features already existed before within the genome. The ability for modification is much more a sign of already existing polyvalence of living beings.

Translator: Sarah Aziz, 07.01.2008

Author: Reinhard Junker

 
© 2008