Evolutionary processes are the basic workings on which almost all of biological thought and explanations are based - it's as much a part of biology as atomic theory is part of chemistry. This presents an interesting set of puzzles - if traits arise because of the advantage they convey on the organism that has them, then there must be a recognizable advantage. Solving the "Why is that there?" puzzle is one of the most interesting aspects of biology. And you can almost always come up with a trait's disadvantages, too - the evolutionary assumption is that the advantages outweigh the disadvantages for this species in its present place.
Remember, in simple terms evolution is found in those changes a type of organism goes through over time to better suit it to its environment, or to increase its fitness. The new traits are considered to be adaptations, which are usually inborn changes that make one or a few individuals in the group better able to deal with the environment. These better-adapted individuals are more likely to live to breed and pass on those advantageous traits, which spread through the population - each generation, more and more of the group reflects the advantageous adaptations of those ancestors, and gradually the basic "plan" of the species changes.
Evolution often is a result of competition between species (predators and prey, parasites and hosts, etc) or between individuals within a species (for mates, for food, for territory, etc.). Any adaptation that supplies an edge in those competitions will probably spread, generation after generation, through the population, changing it.
Many factors influence the value of any adaptation. For instance, any ecosystem is filled with niches, those "slots" or jobs in which particular types of organisms fit. Niches may exist that no group is exploiting, or that can be subdivided between new specialists, giving spaces for new adaptations to move into - new species can arise without replacing the old species in such cases. Groups can be bumped from a niche by others better suited to it - they either move to a new one or die out. Niches themselves may appear and disappear, taking species with them - at the end of the Age of Dinosaurs, large animal niches disappeared, for some reason, and all of the large animals in them vanished.
Another factor to consider is isolation: groups of individuals separated over any long period will start to reflect those good adaptations (they show up randomly - what variations will exist can't be predicted) that have appeared in each group. Over time, the groups, if they stay separate, will be more and more different, sometimes dramatically so, creating new species.
We will try to solve some of the evolution puzzles - decide what advantages
particular traits give to particular species. We'll also look at the downside - what
disadvantages go with each trait? There's no way to tell whether an answer is
absolutely right or wrong - and often many will make sense.
Here we will look at several familiar animals and try to decide, for particular traits found in each species, what advantages and what disadvantages go along? Put answers on the answer sheet provided.
All of the Part One animals are adapted to the African savannah ecosystem: fairly hot, fairly open country, grasslands with occasional stands of trees and bushes, tropically hot with alternating wet and dry seasons.
These you can answer right on the Part Two sheets. These cover other evolutionary ideas - pay attention to the explanations and hints.
First Written 1996; Last Update 2003; Web Version 2001, M. McDarby
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