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.

MODERN CLASSIFICATION

Zebra BookChapter 17 Section 2

Determining Species

• 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.

Typological species concept

• 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

Biological Species Concept

• 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

Phylogenetic Species Concept

• 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

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

TERMS YOU NEED TO KNOW

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

Morphological Characters

• Homologous Characters: shows an anatomical similarity inherited from a common ancestor

• EX. oviraptor and sparrow• What similarities do you see?

http://www.critterzone.com/animal-pictures-nature/bird-sparrow-white-crowned.htm, http://mmfrankford.deviantart.com/art/Oviraptor-Philoceratops-95046955

BIOCHEMICAL CHARACTERS

• 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

http://www.gardeningblog.net/how-to-grow/broccoli/, http://acozykitchen.com/parmesan-and-dill-cauliflower-puree/, http://www.treehugger.com/green-food/weekday-vegetarian-yet-another-version-kale-pesto.html

Species Examples

• 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

MOLECULAR CLOCK

• 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

CLADISTICS• 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

http://en.wikipedia.org/wiki/Phylogenetic_tree

TREE OF LIFE

• 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???