Diversity, Complexity, & Adaptation


A coral reef.

Biological diversity or biodiversityBiodiversity:
The variety and variability among living organisms and the ecological complexes in which they occur.
is the collection of all the differences among life forms within an ecosystem. When organisms are significantly different from one another, they are considered different species, so it is often easiest to discuss biodiversity in terms of species numbers (also called species richnessSpecies Richness:
The total number of species, or biodiversity, in a given geographical area.
). For instance, a coral reef supports much more biodiversity than a fish tank, because the coral reef can easily have hundreds of species within the same volume as a fish tank with only a few species. The coral reef is also more “biodiverse” ecologically — sand, hard coral, rock, algae, seagrass, and soft coral (gorgonians) are often all found within a very small area on a coral reef. Each of these substrata or nichesNiche:
The specific ecological role that an organism inhabits.
has its own habitat specialists occupying it.

New species are being discovered by researchers every day and therefore our understanding of Earth's biodiversity is continually increasing. There are approximately 25,000 living species of bivalves plus at least as many extinct species, each distinct from the others. To fully understand the biodiversity of bivalves evolutionarily, both the living and extinct species must be considered.

Living Neotrigonia lamarcki, from Moreton Bay, Australia (above left), is a living relic — a member of a now-small genus at the Recent end of a large group that flourished in the Cretaceous Period. At right is Pterotrigonia thoracica from the Cretaceous of Coon Creek, Tennessee (also the state fossil of Tennessee). To fully understand this group, both living and fossil species must be studied.

Other types of biodiversity include trophic diversityDiversity:
The variety of species in a sample, community, or area.
(the range of how organisms feed in different ways and/or on different prey), and genetic diversity (the range of genetic variance within a species, that produces, for example, different color forms or subspecies).


Close examination of even the simplest organism often reveals great complexityComplexity:
How the vast and varied components of an organism (genes, molecules, cells, organs) function together to create life, behaviors, species interactions, ecosystems, etc.
in its anatomy, chemistry, and/or behavior. The complexity of an organism must be understood within (and can often provide clues to) the species' evolutionary history.

This externally simple Nut Clam reveals complex anatomy internally (at right).

It is often difficult to understand how complex traits evolved. Researchers must spend enormous efforts using all of their available tools (such as the fossil record, genetic analysis, comparative anatomy, etc.) to understand how complexity evolved through the small favorable steps of natural selection.

Creationists, and those promoting intelligent designIntelligent Design:
The assertion or belief that physical and biological systems observed in the universe result from purposeful design by an intelligent being rather than from chance or undirected natural processes.
, often capitalize upon the difficulty of understanding biological complexity and suggest that complexity is evidence for an intelligent designer. However, given enough time and scientific testing, researchers have been able to show how many complex systems evolved through small advantageous steps over long periods of time. There are still numerous complex systems and structures that have not yet been fully explained, however, this is only due to research not yet completed or to evidence not yet analyzed. Researchers are continuously finding new fossils, discovering new genetic relationships, and understanding additional relationships. Therefore, given sufficient time, more complex systems will be understood. Absence of evidence does not prove anything; a lack of information is not a valid argument against the principles of evolution or for any other theory. A lack of information is merely a signal that more research needs to be done.


The evolutionary process through which a population becomes better suited to its environment over many generations of natural selection.
is the evolutionary process through which a population becomes better suited to its environment over many generations of natural selection. Adaptations can involve anatomy, chemistry, and/or behavior. The word “adaptation” is often misused to describe the physical features of a species which result from the process; however, it is more accurate to call the process “adaptation” and the features “adaptive traitsAdaptive Trait:
A heritable feature of an individual’s phenotype that improves its chances of survival and reproduction in the existing environment.
”. For example, the hard shell of a clam is an adaptive trait that evolved through the process of adaptation to survive crab predation, dessication, etc.

Adaptation in a genus or family can be understood by following an adaptive trait, in progressive steps, through the fossil record. Adaptive traits are responsible for a large proportion of the biodiversity and complexity of the species on Earth.