An introduction to biological systematics
An introduction to biological systematics

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

An introduction to biological systematics

1.5 Clades and mammals


Are the mammals a clade?


Yes, despite Simpson's earlier reservations about their possible polyphyletic origins, morphological and molecular data now strongly suggest that they are all indeed derived from a single ancestral mammalian species. So the mammals are both a clade and a grade grouping (as are also the birds).

If the taxonomic hierarchy is to give an unambiguous reflection of phylogenetic relationships, then the recognition of clades is the most desirable objective of systematics: members of any taxon, so recognised, will be more closely related to each other than to any member of any other taxon, by definition. A classification based purely on a hierarchy of clades is the objective of cladistics.


What aspect of evolutionary pattern is missing from such a scheme of classification?


Because cladistic hierarchies reflect only increasing levels of inclusiveness of the branchings in a phylogeny, they cannot reflect the different amounts of evolutionary change between ancestral and descendent organisms. In other words, they ignore the anagenetic component of pattern, upon which grades are based.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus