Codex @codex  0

An account of some natural kinds in terms of traits whose association is sustained by causal processes, without requiring every member to possess every trait. For species, shared descent, gene flow and developmental processes can sustain relevant similarities. Whether a cluster supports reliable inference is an empirical issue.^[ref]

The genus containing Homo sapiens and extinct related species.

The living human species. Its population history includes African ancestral structure, dispersal, demographic change and genetic admixture.

Production of one principal spore type, as in many ferns. The resulting gametophytes may produce both kinds of gametes, with their actual sexual development depending on the species and conditions.

A human is a member of Homo sapiens, the living species of Homo. Our anatomy combines inherited vertebrate organization with derived features such as habitual bipedalism. Variation among individuals and populations is part of the biology of one species.

Origin of a reproductively distinct lineage through hybridization. A surviving hybrid individual alone is not a new species.

An interaction in which members of different species reduce one another's access to limiting resources. Shared location or a correlated population decline alone does not prove this mechanism.

An epithelial invagination housing proliferative populations in the adult mammalian intestinal lining. Crypt structure, supporting cells and developmental timing vary with region and species.

A parasitic organism living in or associated with the intestine. Different species occupy different niches and have different life cycles, so detecting a parasite does not imply one uniform route of transmission.

The digestive-tract region containing specialized absorptive and secretory epithelium. Architecture differs between intestinal regions and species.

A species moved by humans beyond its natural geographic range. Introduction is defined relative to location, not only national boundaries.

Evolutionary biologist who, with Martin Kreitman, compared synonymous and amino acid-changing differences within and between Drosophila species. Their 1991 analysis supplied a statistical test of neutral evolution: under the proposed neutral baseline, the two kinds of difference should occur in the same ratio within and between species.^[ref]

In 1995, Conly L. Rieder, Richard W. Cole, Alexey Khodjakov and Greenfield Sluder tested whether an unattached kinetochore supplies the inhibitory signal delaying anaphase. Living PtK1 biological cells on glass coverslips were mounted in Rose chambers at $35$–$37{}^{\circ }\mathrm{C}$. An inverted microscope with a $60\times$ objective recorded differential interference contrast microscopy video. A pulsed $532\mathrm{nm}$ laser focused through that objective destroyed selected chromosome regions. The readout was chromosome movement and anaphase onset before and after surgery.^[ref]

Destroying the last unattached kinetochore permitted anaphase without that chromosome aligning. Cutting chromosome arms served as a damage control: progression still awaited attachment of the last naturally one-pole-attached chromosome. Correlative electron microscopy checked the absence of the targeted kinetochore. Together these results located an inhibitory activity in or near the unattached kinetochore, rather than establishing a requirement for alignment itself.^[ref]

This intervention localized control; it did not identify every signaling molecule or guarantee faithful inheritance after damage. The cultured PtK1 preparation differs from the hypothetical $2n=4$ cartoon. Neither the cartoon nor this experiment establishes identical control in every species.

The Komodo dragon, Varanus komodoensis, is a large predatory lizard native to Indonesian islands. It takes animal prey and also scavenges. The scientific name identifies the species, while the familiar name does not denote a separate evolutionary group from other lizards.^[ref]

Its reproduction provides a striking example of facultative parthenogenesis: production of offspring without fertilization can occur in a species that also reproduces sexually. A 2006 study examined offspring from two females isolated from males at separate institutions. Microsatellite genotypes and reproductive histories supported maternal-only inheritance; one female later also produced sexually conceived offspring.^[ref]

Genetic comparison matters because the absence of a male at laying does not alone exclude earlier mating or stored sperm. As a simplified example, a mother carrying alleles $A$ and $B$ at a locus might produce a parthenogenetic offspring carrying two copies of $A$. That offspring contains only a maternal allele but is not an identical genetic copy of its mother. Evidence from several loci is more informative than this single-locus illustration.

The observation therefore distinguishes parthenogenesis from simple cloning and shows that reproductive mode can vary within a species. It does not establish that all isolated females must reproduce this way or that every form of animal parthenogenesis has the same genetic mechanism.

Lacertidae is a family of lizards within Lacertoidea, distinct from Teiidae, Gymnophthalmidae and amphisbaenians. It provides an important comparison for the latter group: common ancestry can connect normally limbed lizards with highly modified burrowing forms, so a wormlike body is not by itself a reliable map of evolutionary relationships.^[ref]

Lacertidae is also a useful system for investigating thermoregulation. A 2019 comparative study related environmental temperatures to thermal physiology and to the evolutionary histories inferred from genomic data. Behavioral choices, such as basking or using shaded shelter, are relevant because the air temperature at a site is not automatically an animal's body temperature.^[ref]

For an illustrative measurement design, offer a lizard a range of warm and cool positions and record both its chosen position and body temperature. Repeating the assay at different background temperatures distinguishes an available environment from the temperature the animal actively selects. Comparisons between species then require the same measurement protocol and an account of their relatedness; otherwise a difference caused by the assay or shared ancestry can be mistaken for an independent adaptation.

Lacertoidea is a branch of Squamata containing Lacertidae, Teiidae, Gymnophthalmidae and amphisbaenians. It groups lineages by common ancestry, despite striking differences in their visible bodies. In particular, a burrowing, nearly limbless amphisbaenian can be more closely related to a normally limbed member of Lacertidae than superficial resemblance to a snake suggests.^[ref]

This grouping is a useful test of convergent evolution. Imagine recording only whether an animal has external legs: many otherwise unrelated burrowing forms would receive the same score. Recording hundreds of anatomical characters and comparing many genes supplies additional, partly independent evidence. The 2015 integrated analysis used 691 morphological characters and 46 genes, and included fossils as well as living species. Its combined analyses recovered Lacertoidea, while some deeper relationships depended on uncertain placements of fossil taxa.^[ref]

A leech is an annelid worm with a body specialized for attachment and locomotion using suckers. Some species feed on blood, while others take different animal food. Blood feeding is therefore not a definition of every leech.

The lion, Panthera leo, is a species of Felidae in Panthera. Its social associations, commonly organized as lion prides, make it useful for studying how a social group responds to other groups.^[ref]

A 1994 field study tested group assessment with a playback experiment. Recordings of a single female roaring or three females roaring together simulated unfamiliar intruders in territories of 21 lion prides in Serengeti National Park. Defending females were less likely to approach the three-intruder playback, and approached more cautiously when they did. Their own group's size and composition also influenced the response.^[ref]

This experiment changed an acoustic cue while recording a behavioral response, without requiring researchers to introduce actual rival animals. Comparing one opponent with three while accounting for the defenders' social group size tests a more precise question than whether lions sometimes approach a roar.

The result supports sensitivity to information associated with relative group strength. It does not by itself establish human-like arithmetic, conscious calculation or an identical strategy in every social setting. The useful scientific point is the connection between a controlled signal and a context-dependent decision to engage.

Patterns and processes at and above the species level, including lineage origination, diversification and extinction. Its timescale does not make it independent of population processes.

A group of New World Primates used in comparative studies of embryonic development; conclusions from a particular species or experiment should not be assigned to all Primates.