1. Systematics
Systematics is the science of categorizing organisms into like groups and
establishing their relationship relative to each other.
Eight major categories are used to classify organisms:
domain
kingdom
phylum
class
order
family
genus
species

2. Systematics In case of humans: Eukarya domain: kingdom: phylum:
class:
order:
family:
genus:
species:
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens

3. Systematics But how do we establish the groups of organisms?
1. Phenetic classification
2. Cladistic classification (Phylogenetic)
3. Evolutionary taxonomy
Although these three approaches give similar results,
there are often some major differences. There is no
“correct” way, and biologists are still trying to decide
on the best way of classifying organisms.

4. Systematics – Domains and Kingdoms
Note that Taxonomies are constantly changing. Part of the reason is new information
(mostly based on molecular biology) being discovered about different groups.
* Some of the reasons though are purely political!!
* Since there is no absolute “correct way”, it is all about how we define the
species concept.

5. Systematics –Kingdoms
Relationships are not quite as
simple as suggested by this figure.
Ideally, each branch point is where a new form
(i.e. adaptation) has created two distinct forms
from a single common ancestor.

6. Systematics – Evolutionary Connections
Monophyletic versus Polyphyletic groups
Ideally, we want monophyletic groups where all members have one common
ancestor. Under this definition, “Reptiles” are not a good group.