CHAPTER 4: THE FORCES OF EVOLUTION AND THE FORMATION OF SPECIES

HOW NATURAL SELECTION WORKS “Natural selection takes the package of traits each animal or plant inherits from the previous generation and then alters it in response to the current environment. Natural selection is not simply about genes and traits. The environment is the filter through which traits – and the genes that control their expression – are selected for or against.”

DARWIN’S FINCHES – THE GOOD AND THE BAD?

KEY TERMS – I.E. EXTREMELY IMPORTANT TERMS Gene flow : movement of genes between populations Inbreeding : mating between close relatives. Genetic drift : random changes in gene frequency in a population. Founder effect : a component of genetic drift theory, statin that new populations that become isolated from the parent population carry on the genetic variation of the founders. Genetic bottleneck : temporary dramatic reduction in size of a population or species.

GENE FLOW

GENETIC DRIFT

GENETIC BOTTLENECK

FOUNDER EFFECT

Sexual selection : differential reproductive success within one sex of any species. SEXUAL SELECTION

Sexual dimorphism : difference in size, shape, or color between sexes. SEXUAL DIMORPHISM

CLASSIFICATION AND EVOLUTION

KEY TERMS Systematics : branch of biology that describes patterns of organismal variation. Homology : similarity of traits resulting from shared ancestry. Analogous : having similar traits due to similar use, not due to shared ancestry. Convergent evolution : similar form or function brought about by natural selection under similar environments rather than shared ancestry. Cladistics : method of classification using ancestral and derived traits to distinguish patterns of evolution within lineages. Cladogram : branching diagram showing evolved relationships among members of a lineage.

HOMOLOGY AND ANALOGY

CLADOGRAM

WHAT IS A SPECIES? Species : an interbreeding group of animals or plants that are reproductively isolated through anatomy, ecology, behavior, or geographic distribution from all other such groups. Speciation : formation of one or more new species via reproductive isolation.

LIGER

A GUIDE TO SPECIES CONCEPTS Biological species concept : defines species as interbreeding populations reproductively isolated from other such populations. Evolutionary species concept : defines species as evolutionary lineages with their own unique identity. Ecological species concept : defines species based on the uniqueness of their ecological niche. Recognition species concept : defines species based on unique traits or behaviors that allow members of one species to identify each other for mating.

REPRODUCTIVE ISOLATING MECHANISMS (RIMS) Any factor – behavioral, ecological, or anatomical – that prevents a male and female of two different species from hybridizing.

Anagenesis : evolution of a trait or species into another over a period of time. Cladogenesis : evolution through the branching of a species or a lineage. ANAGENESIS AND CLADOGENESIS

SPECIATION Allopatric speciation : speciation occurring via geographic isolation. Paprapatric speciation : speciation occurring when two populations have continuous distributions and some phenotypes in that distribution are more favorable than others. Sympatric speciation : speciation occurring in the same geographic location.

MACROEVOLUTION AND MICROEVOLUTION

Gradualism : Darwinian view of slow, incremental evolutionary change. Punctuated equilibrium : model of evolution characterized by rapid bursts of change, followed by long periods of stasis. GRADUALISM AND PUNCTUATED EQUILIBRIUM

ADAPTION Adaptionism : a premise that all aspects of an organism have been molded by natural selection to a form optimal fro enhancing reproductive success. Holists would point out that the chin is only the meeting point of the two halves of the lower jaw, which do not fuse until infancy in human development. The chin exists because of the position of the teeth, not because the chin has any adaptive role of its own. Reductionism : paradigm that an organism is the sum of many evolved parts and that organisms can best be understood through an adaptionist approach.