ABSTRACT BASIC TYPES OF LlFEl

BASIC TYPES OF LlFEl SIEGFRIED SCHERER, PH.D. ARIBOSTRASSE 18, 0·85356 FREISING, GERMANY The main conflict In the species discussion may be summarized as follows: the population geneticist is mainly Interested in gene flow and, therefore, has to prefer a biospecies concept. On the other hand, the practicing taxonomist and the palaeontologist are mainly interested in similarity and, hence, have to use a morphological species concept. This conflict is fundamental and cannot easily be resolved. It is often stated that higher levels of classification are even more problematic than the species definition. Using a genetical criterion based on InterspecifiC hybridization, it is suggested that a systematic category above the genus level may be defined rather objectively: two organisms belong to the same basic type If (I) they are able to hybridize or (ii) they have hybridized with the same third organism. In principle It Is possible to check experimentally by artificial insemination or artificial pollination if two biparental individuals belong to the same basic type. The basic type category thus may prove to be open to empirical validation. Advantages and problems of this basic type criterion are discussed. A general summary follows on a few basic types of the plant and animal kingdom that have been described. Based on rather limited data it appears to emerge that (i) the basic type criterion can be applied successfully in animal as well as plant taxonomy, (Ii) a clear gap of overall similarity Is found between different basic types, (iii) within basic types a variety of mlcroevolutionary processes may help to understand speciation, and (iv) the distribution of characters across different species of the same basic type may be discussed under the hypothetical assumption of a large hidden variation potential harboured by a genetically complex ancestral population. It must be emphasized that only 14 basic types have been described to date. This number is too low to provide for a reliable basis of generalization. Therefore, the basic type concept is only suggested to serve as a preliminary working hypothesis. (I) THE SPECIES PROBLEM Currently, about 1.5 million species are binominally named. However, this is probably only a fraction of the total number of extant species. Estimates vary between 3-5 millions and 10-50 millions (May 1988). For four reasons, it is necessary to name the species on earth. First, only by naming is it possible for biologists to communicate on their subjects. Second, only by naming is it possible to classify. Third, only by naming is it possible to understand the mechanisms of mlcroevolution, I.e. speciation and fourth, only by naming Is It possible to protect the threatened diversity of life. Therefore, classification of organismic diversity remains one of the most important as well as most fascinating tasks of biology. (Unfortunately, there is an irritating world-wide tendency to reduce funding for such fundamental researCh.) The numbers of species given above are rather unreliable estimates. In part, this is due to some uncertainty of species definitions. Very often, systematic studies, for practical reasons. , cannot avoid using a morphospecles definition. The definition of the biological species (see below) Is not usually applicable in field or museum studies. This causes an on-going conflict In taxonomy. Dobzhansky wrote: ''The species problem is the oldest in biology" (Dobshansky 1972). Although there Is a seemingly endless discussion of the species problem In the biological literature, it is still unsolved. The discussion has a long history, which Is not to be summarized in this paper (see, e.g., Mayr 1982; Willmann 1985). Neither shall I present the various philosophical implications of the species definition (see, e.g., Sucker 1978; Van der Steen & Voorzanger 1986; Ereshefsky 1992). Numerous species definitions (for review see, e.g., Hauser 1987) as well as speciation mechanisms (for review see l Thls paper is reprlnled from the monograph, Basic Types 01 Ule, edHed by Slegrled Scherer, Berlin, 1993, pp.l130.