Zebra Book Chapter 17 Section 2

Not always easy to define a species Organisms that are one species by a certain definition could be another species by a different definition As knowledge increases, definitions change The concept of a species today is much different than it was 100 years ago.

Classification is based on comparison of physical characteristics with a type specimen LIMITS: alleles produce a wide variety of features within a species BENEFITS: descriptions of type specimens provide detailed records of physical characteristics of many organisms Example… Humans

1930s-1940s Classification is determined by similar characteristics and the ability to interbreed and produce fertile offspring LIMITS: some organisms, such as wolves and dogs, can interbreed and produce fertile offspring but are still separate species. Does not account for extinct species or those which reproduce asexually BENEFITS: works in most cases, so still used frequently

Late 1940s Companion to B.S.C. PHYLOGENY: evolutionary history of a species Classification is determined by evolutionary history LIMITS: evolutionary history is not known for all species BENEFITS: accounts for extinct species and considers molecular data

Inherited features that vary among species Used to construct patterns of descent Morphological or Biochemical

HOMOLOGOUS: anatomically similar, functionally different EX. Bird wing and Human Arm ANALOGOUS: anatomically different, functionally similar EX. Fish gill and human lung

Homologous Characters: shows an anatomical similarity inherited from a common ancestor EX. oviraptor and sparrow What similarities do you see?

Use amino acids and nucleotides to determine evolutionary relationships Also chromosome number and structure EX. Broccoli, Cauliflower and Kale All same Family (Cruciferae) but look completely different

Molecular data has changed traditional taxonomic categorization (DNA and RNA) For example: African Savannah Elephant, African Forest Elephant and Asiatic Elephant Asiatic Elephant is Elephas maximus and both the African elephants are Loxodonta africana even though the two types of African elephants have several different traits Recent studies show that the two African elephants diverged from a common ancestor about 250 million years ago therefore scientists have considered renaming the forest elephant Loxodonta cyclotis

A model that is used to compare DNA sequences from two different species to help determine how long the species have been evolving since they diverged from a common ancestor CONVERGENT EVOLUTION: two organisms who are evolving traits which are similar DIVERGENT EVOLUTION: two organisms from a common ancestor which develop different traits

A METHOD WHICH CLASSIFIES ORGANISMS ACCORDING TO THE ORDER THAT THEY DIVERGED FROM A COMMON ANCESTOR CLADOGRAM: A BRANCHING DIAGRAM THAT REPRESENTS THE PROPOSED PHYLOGENY OF A SPECIES OR GROUP

Charles Darwin used the analogy of a tree to suggest that the majority of organisms developed from a few species Tree Trunk represented ancestral groups, each of the branches to have similar species and the leaves were living species This represents the diversity of living organisms Currently there have been 1.75 million species described and more are found every year HOW LARGE WOULD A TREE INCLUDING ALL KNOWN ORGANISMS BE???