4.5 species and taxonomy

Two populations can mate and produce offspring, but the offspring are infertile. What does this suggest about their species status?

They are not the same species, because the definition requires fertile offspring.

Explain the role of courtship behaviour in species recognition.

Species-specific courtship signals help individuals recognise suitable mates of the same species and reduce mating with other species.

What is the biological definition of a species?

A species is a group of organisms that can interbreed to produce fertile offspring.

How can courtship behaviour act as a necessary precursor to successful mating?

It helps synchronise and stimulate mating responses (eg, readiness to mate), increasing the chance of successful fertilisation.

What is a taxon (plural taxa)?

A named group in a classification hierarchy.

How is the binomial name Homo sapiens constructed (what does each word represent)?

Homo is the genus

sapiens is the species.

Why is fertility of offspring important in defining a species (rather than just ability to mate)?

Fertile offspring allow genes to be passed on to the next generation, showing the populations share a gene pool.

What is the aim of a phylogenetic classification system?

To arrange species into groups based on their evolutionary origins and relationships.

In a hierarchy with no overlap between groups, what must be true about an organism’s membership of taxa at each level?

At each level it belongs to one and only one taxon, and each lower-level taxon is contained within a higher-level one.

How can advances in immunology help clarify evolutionary relationships between organisms?

By comparing immune-related molecules/responses to infer similarity, closer similarity suggests a closer evolutionary relationship.

What is courtship behaviour, in the context of mating?

A set of behaviours/signals that occur before mating, which can be necessary to trigger successful mating.

How does a phylogenetic classification system organise taxa (groups)?

It uses a hierarchy: smaller groups are placed within larger groups, and there is no overlap between groups.

What is a binomial name, and what two parts does it contain?

A universal species name consisting of the genus name and the species name.

How can advances in genome sequencing help clarify evolutionary relationships between organisms?

By comparing DNA/genome sequences

more similar sequences indicate a more recent common ancestor.

List the taxa in the hierarchy used in one phylogenetic classification system (largest to smallest).

Domain, kingdom, phylum, class, order, family, genus, species.

Why is binomial nomenclature described as a universal identification system for species?

It provides a standard name used worldwide, reducing confusion from different local/common names.

What is a species?

A group of similar organisms that can interbreed to produce fertile offspring.

Why must members of the same species be able to produce fertile offspring?

Fertility ensures they share the same gene pool and pass genes on to future generations.

Why can members of different species not produce fertile offspring?

Genetic incompatibilities prevent normal meiosis in hybrids.

Why is reproductive isolation essential for maintaining species boundaries?

It prevents the mixing of gene pools so species remain distinct.

What is courtship behaviour?

A sequence of behaviours used during mating.

Why is courtship behaviour species-specific?

Because each species has a unique, genetically determined pattern of signals and responses.

How does courtship behaviour help individuals recognise members of their own species?

Only individuals with the correct, species-specific signals will respond.

Why is recognising the same species essential for successful mating?

It ensures mating only occurs between compatible partners capable of producing fertile offspring.

How does courtship behaviour ensure synchronisation of mating?

It ensures mating occurs when both individuals are fertile and ready.

How does courtship behaviour identify sexually mature and receptive mates?

It indicates readiness and physiological suitability to mate.

Why does courtship behaviour improve the probability of successful fertilisation?

It increases the chance of mating between compatible individuals.

Why is courtship behaviour important in preventing interbreeding?

Incorrect courtship signals prevent mating attempts between different species.

How can courtship sequences act as a pre-zygotic isolating mechanism?

They prevent mating and fertilisation before a zygote can form.

Why does natural selection favour effective and precise courtship rituals?

More effective rituals lead to higher reproductive success.

What is classification?

The process of organising living organisms into groups.

What is taxonomy?

The science of classification.

What is the purpose of a hierarchical classification system?

To arrange organisms into groups reflecting evolutionary relationships.

What is a taxon?

A named group within a classification hierarchy.

What is the basic unit of biological classification?

The species.

What is a hierarchy in biological classification?

A system in which smaller groups are placed within larger groups.

Why do groups in a classification hierarchy not overlap?

Each organism belongs to only one group at each level.

What does each higher level of the hierarchy contain relative to the one below?

It contains more organisms, but those organisms share fewer common features.

What are the main taxonomic ranks in order from largest to smallest?

Domain, kingdom, phylum, class, order, family, genus, species.

Why is each lower taxonomic rank more specific than the one above it?

Members share more features because they are more closely related.

Why do organisms in the same genus share more similarities than organisms in the same family?

They share a more recent common ancestor.

What is the binomial naming system?

A universal system giving each species a two-part scientific name.

Why does the binomial system use Latin or Greek?

These languages are not tied to any modern language and remain stable over time.

What does the first name in a binomial scientific name represent?

The genus.

What does the second name in a binomial scientific name represent?

The species identifier.

Why must scientific names be universally recognised?

To prevent confusion across different languages and regions.

Why does binomial naming reduce confusion in scientific communication?

Every species has one universally recognised global name.

Why is classification increasingly based on evolutionary relationships rather than physical features alone?

Evolutionary relationships provide more accurate groupings.

What is phylogeny?

The evolutionary history of a species or group.

Why do phylogenetic trees show common ancestry?

They trace lines of evolutionary descent from common ancestors.

What does each branch point on a phylogenetic tree represent?

A point where one lineage split into two.

What does the length of branches sometimes indicate on phylogenetic trees?

The amount of evolutionary change or time elapsed.

Why do species closer together on a phylogenetic tree share more recent common ancestors?

They diverged more recently and share more inherited traits.

Why is phylogeny more reliable than traditional classification based solely on morphology?

Morphology may converge due to environmental pressures, whereas DNA reflects true ancestry.

How does comparing DNA base sequences help classify organisms?

More similar base sequences indicate closer evolutionary relationships.

How does comparing amino acid sequences help classify organisms?

More similar amino acid sequences in shared proteins indicate shared ancestry.

Why do more similar DNA sequences imply closer evolutionary relationships?

Fewer mutations accumulate when divergence occurred recently.

Why does natural selection cause DNA sequences to diverge over time?

Different selection pressures cause gradual accumulation of genetic differences.

Why is genetic comparison more objective than observable characteristics?

It avoids subjective interpretation based on appearance.

Why can observable features be misleading due to analogous structures?

Different species may evolve similar traits due to adapting to similar environments.

What are homologous structures?

Structures inherited from a common ancestor.

Why are homologous structures useful in understanding evolutionary relationships?

They show shared evolutionary pathways despite functional differences.

What are analogous structures?

Structures with similar function but independent evolutionary origin.

Why are analogous structures not useful evidence of common ancestry?

They arise from convergent evolution rather than shared ancestry.

What is artificial classification?

Grouping organisms by superficial or arbitrary characteristics.

How does artificial classification differ from natural/phylogenetic classification?

Artificial classification is based on shared function, while natural classification is based on shared ancestry.

Why is natural classification preferred in modern biology?

It reflects true evolutionary relationships.

How does courtship behaviour support biological classification?

Shared courtship patterns reflect shared evolutionary ancestry.

How can molecular evidence confirm or change existing classification groups?

Molecular data can confirm or revise existing taxonomy based on objective genetic evidence.

Why can advances in DNA sequencing lead to reclassification of species?

Because DNA evidence may show species are more or less related than previously thought.

Why does classification allow scientists to predict characteristics of organisms?

Related species often share characteristics due to shared ancestry.

Why is understanding evolutionary relationships important for medical and agricultural research?

It helps predict disease spread and improve breeding programmes or treatments.

Why does taxonomy help identify species at risk of extinction?

It identifies unique evolutionary lineages and hotspots of genetic diversity.