30

4

Evolution

4.1

Phylogeny and Evolution

Classical Darwinian theory ⁴ is founded on two observed facts:

1. There is (inheritable) variety among organisms.

2. Despite fecundity, populations remain roughly constant.

From these Darwin inferred that population pressure leads to the elimination of

descendants less able to survive than slightly different congeners. Formally, there-

fore, evolution is a problem of selection. Only certain individuals (or species—see

Sect. 4.1.1) are selected to survive. It is practically synonymous with natural selec-

tion, the “natural” being somewhat redundant.

Modern evolutionary theory is especially concerned with the following: ⁵

1. The levels at which change occurs (e.g., genes, cell lineages, individual organisms,

species). Darwin dealt with individual organisms (microevolution); macroevolu-

tion deals with mass extinctions.

2. The mechanisms of change corresponding to the levels. The root of inheritable

variation lies in the genes, of course; investigations of mechanisms operating

at the higher levels subsume the lower-level mechanisms. The investigation of

macroevolution has to deal with unusual (rare) events, such as the collision of

Earth with a large meteor, and with avalanches of extinctions facilitated by trophic

and other interactions between species.

3. The range of effects wrought by natural selection, and the timescales of change.

Critiques of classical Darwinism are legion. Inter alia, one may note the following:

The selectionist explanation is always a construction a posteriori; evidence cited in

favour of natural selection is often inconsistent, hence rules are difficult to discern ⁶—

all one can say is that every surviving form must have been viable (i.e., having some

selective advantage) or it would not have survived, and this is, of course, no proof

that it is a product of selection; there appears to be no essential adaptive difference

between specialization and nonspecialization—both are found in abundance; selec-

tion presupposes all of the other attributes of life, such as self-maintenance, adapt-

ability, reproduction, and so forth, hence it is illogical to assert that these attributes

are the result of selection; there is no evidence that progression from simple to

complex organisms is correlated with better adaptation, selective advantage, or the

4 It is fairly well known that both Darwin and Wallace contributed independently; perhaps less well

known is that (European) priority appears to belong to Matthew (1831). Insofar as the Chinese were

selectively breeding fancy goldfish several centuries earlier, global priority belongs to them.

5 The term “evolution” was originally applied to the development of an organism from its starting

cell, through to birth (if later), adulthood and throughout life (cf. Sect. 14.9).

6 Examples: what is the selectionist advantage of the onerous migration of Comacchio eels to

the Sargasso Sea for breeding? Why does the cow have multiple stomachs, whereas the horse (a

herbivore of comparable size) has only one? Why do some insects adopt marvellous mimickries

allowing them to be concealed like a leaf, whereas others, such as the cabbage white butterfly, are

both conspicuous and abundant?