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

1.3 Relationships between species

SAQ 1

Using the idea of blood relationships in people as an analogy, can you think of two distinct types of relationship between species?

Answer

One is the relationship of descent – as in the parent–child relationship – and the other is that of shared parentage, as with brothers and sisters. Similarity between species may reflect either of these two kinds of relationship. It would be misleading to push the analogy too far, though, for two reasons. First, with the exception of allopolyploid hybrid species, new species are derived from single parental species. Secondly, a newly evolving species derives its characteristics directly from those currently present in the ancestral population: there is nothing in a species population that corresponds to the unchanging germ line of individual parent organisms. Two fundamental patterns of change in a phylogeny thus give rise to the differences between related species: anagenesis refers to descent with modification, within any given single lineage; and cladogenesis refers to the evolutionary division of lineages causing a proliferation of species. The grouping of species to form higher taxa can emphasise either or both of these components of phylogeny (Figure 1).

S365_1

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