analogous structures: Structures in different species that look alike or perform similar functions (e.g., the wings of butterflies and the wings of birds) that have evolved convergently but do not develop from similar groups of embryological tissues, and that have not evolved from similar structures known to be shared by common ancestors. Note: The recent discovery of deep genetic homologies has brought new interest, new information, and discussion to the classical concepts of analogous and homologous structures.anatomy: (1) The structure of an organism or one of its parts. ancestral homology: Homology that evolved before the common ancestor of a set of species, and which is present in other species outside that set of species. anthropoid: A member of the group of primates made up of monkeys, apes, and humans.

acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weightlifter).

adaptation: Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment.

Peaks on the landscape correspond to genotypic frequencies at which the average fitness is high, valleys to genotypic frequencies at which the average fitness is low. adaptive logic: A behavior has adaptive logic if it tends to increase the number of offspring that an individual contributes to the next and following generations.

If such a behavior is even partly genetically determined, it will tend to become widespread in the population.

They have moist scaleless skin which is used to supplement the lungs in gas exchange.

The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water.

amphibians: The class of vertebrates that contains the frogs, toads, newts, and salamanders.

The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land.

Also used to describe the process of genetic change within a population, as influenced by natural selection.

adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it.

allometry: The relation between the size of an organism and the size of any of its parts.