Taxonomy and Phylogeny

How many species are there?Assumptions:

• Humans can agree on how to define a species…

— biological

— geographical

— molecular

• The murky definition of a species can be

applied to asexual microbes…

Scientists’ best guess…

• There are 8.7 million +/- 1.3 million extant eukaryotic species

• 1.2 million have been classified• 14% of land species (86% undiscovered)

• 9% of marine species (91% undiscovered)• Remember, estimates are that somewhere between 25-200 species go extinct

every day – Holocene Mass Extinction

• Estimates of the number of extant prokaryotic species range from millions to 10,000,000,000,000 (10 trillion)(1 per second = 317,098 years)

• Estimates are that 99% of all species that ever lived are currently extinct

• That would mean up to 1 quadrillion species have existed (1,000,000,000,000,000)(1 per second = 31,709,792 years)

Taxonomy is the branch of biology that produces a formal classification

system for organisms.

Taxonomy was first formalized by Swedish botanist Carolus

Linnaeus in 1735.

His system divided organisms into plants and animals based

on a hierarchical system.

A taxon (pl. taxa) is a category that contains related

organisms.

Taxa are subdivided from broadest (most inclusive) to

narrowest (least inclusive) groups.

The most specific classification is a species.

Each species is given an unique name denoted by both its genus and species.

Names are often based in Latin or Greek, but not always…

The genus is always capitalized, the species is not capitalized.

Genus-species is always italicized or underlined.

The genus can be abbreviated by using the first letter and a period and then the species written out.

Loxodonta africana L. cyclotis Wockia chewbacca

Two primary benefits:

1. minimizes communication confusion amongst scientists

2. provides clues to evolutionary relatedness

Describe a neko…

Levels of Classification

Domain

Kingdom

Phylum

Genus

Species

Class

Family

Order

Eukarya

Animilia

Chordata

Mammilia

Carnivora

Alopex

Canidae

lagopus

Alopex lagopus

Arctic Fox

Modern Human Classification

Eukarya

Animalia

Chordata

Mammalia

Primates

Hominidae

Homo

sapiens

*Honors

Additional Taxa

Additional levels are often used in order to be more

precise; these are denoted by prefixes and suffixes.

super and infra denote a level above

– e.g. infraclass or superfamily

sub indicates a level below

– e.g. subspecies

Tribe is an additional taxon falling between family

and genus. It is often used in plants and insects, but

is also used in primate classification.

Domains

Eukarya KingdomsProtista – heterotrophic or autotrophic (photosynthesis only),

single celled and/or communal, most aquatic; e.g. protozoans,

algae

Fungi – multicellular, absorptive heterotrophs, chitin cell walls

Plantae – multicellular, autotrophic, photosynthesis,

cellulose cell walls

Animalia – multicellular, ingestive heterotrophs, most motile

Kin

gd

om

An

ima

lia

Classification Reflects Evolution

Determining Evolutionary Relationships

Modern Taxonomy (also sometimes called systematics) relies primarily on the following:

-- Comparative morphology

Compares structures between species

-- Comparative embryology

Compares development of embryos

-- Comparative biochemistry

Compares proteins (amino acid sequences) and nucleic acid sequences (RNA and DNA)

-- Comparative cytology

Compares number, type, and shape of chromosomes

**note the commonality: COMPARE

Comparative Morphology – homologous structures

These are all tetrapods, descended from a

common ancestor.

Analogous structures are not homologous structures…

analogous structure: similar function, different structure; not shared by common ancestor

Comparative Embryology – similar embryos

Comparative Biochemistry and Cytology

Cladistics Terms

character – any feature used to

study variation within and

among species; can be

morphological, chromosomal,

or molecular (in this class, we

will focus on morphological)

ancestral character – the

character state that was present

in the most recent common

ancestor of the taxon (also

called primitive character)

derived character – all other

contrasting versions of the

ancestral character

IMPORTANT: These are relative terms! They only work when used together.

Cladogram

clade (Gr. klados, branch) –

fundamental unit of grouping species;

comprises an ancestral linage and all

species descended from that linage.

All members of a clade will share a

derived characteristic.

Nesting multiple clades creates a

cladogram that shows evolutionary

relationships.

**For the purposes in this class, cladogram and phylogenic tree are used interchangeably.

Hominid Evolution

Genus Homo

In zoology, “human” is defined as any animal

within the genus Homo.

The exact path of evolution of this genus is still

being worked out.

Current information indicates it evolved about

2.3 million years ago and, so far, scientists

have identified 7 species of human.

Homo erectusAfrica and Asia

1.89 mya-143,000 ya

Homo rudolfensisAfrica

1.9-1.8 mya

Homo floresiensisIndonesia

100,000-50,000 ya

Homo sapiensGlobally

300,000-present

(has 2-5% neanderthal DNA in non-African lineage)

Homo heidelbergensisAfrica, Europe, Asia

700,000-200,000 ya

Homo habilisAfrica

2.4-1.4 mya

Homo neaderthalensisEurope and Asia

400,000-40,000 ya