(a) Describe the stages of human evolution and mention the major hominid forms giving their time of origin. (20 marks) (b) What…

Human evolution is best described as a sequential record of hominid forms in which bipedalism, brain enlargement, dental reduction and tool use became progressively linked. Stages and hominid forms. In the Miocene, early apes such as Dryopithecus (~12–9 Mya) and Ramapithecus (~14–8 Mya) provide the background for hominid origins; Ramapithecus was historically debated as a hominid relative but is not accepted as a bipedal ancestor. In the Pliocene and early Pleistocene, Australopithecus appears: A. anamensis (~4.2–3.9 Mya), A. afarensis (~3.9–2.9 Mya, represented by Lucy), and A. africanus (~3.3–2.1 Mya, represented by the Taung Child). These forms show habitual bipedalism, cranial capacities of about 400–550 cc, reduced canines and jaws, and little consistent tool use. Homo habilis (~2.4–1.4 Mya) marks the first clear association of larger brains (~500–700 cc) with Oldowan stone tools and further dental reduction. Homo erectus (~1.9–0.3 Mya) shows cranial capacity rising to about 800–1200 cc, Acheulean tools, probable control of fire, and wider dispersal. Homo neanderthalensis (~0.4–0.04 Mya) in Europe and western Asia had a large brain (~1200–1700 cc), robust body, and advanced stone-tool behaviour. Homo sapiens (~0.3 Mya to present) originated in Africa, with cranial capacity around 1300–1500 cc, symbolic behaviour, complex tools and global expansion. Across these stages, the post-cranial skeleton indicates bipedalism before major brain expansion, while the dentition and skull show reduction of jaw and tooth size as diet and tool use changed.

Hardy-Weinberg law. The Hardy-Weinberg law states that allele and genotype frequencies in a population remain constant from generation to generation when the population is large, mating is random, and there is no mutation, selection, migration or genetic drift. For two alleles A and a, with frequencies p and q, p + q = 1 and the genotype frequencies are p² + 2pq + q² = 1, where p² is homozygous dominant, 2pq heterozygous and q² homozygous recessive. The law is a null model: if observed genotype frequencies deviate from p², 2pq and q², one or more assumptions are being violated. Mutation changes gene frequency by converting one allele into another and by introducing new alleles; it is the raw material of evolution. Mutation pressure may be directional, when one allele changes into another more often, or non-directional/balanced when back mutation occurs. Mutation rates are usually low, so mutation alone changes frequencies slowly, but it continually supplies variation on which selection and drift act. Genetic drift changes gene frequency by random sampling error, especially in small populations. It can fix or eliminate alleles regardless of fitness. Drift is stochastic; its effect is inversely related to population size, so isolated or fragmented populations may diverge rapidly. Bottleneck effects, where a population is sharply reduced, and founder effects, where a small group colonises a new area, are special cases of drift.

Systematics and taxonomy. Systematics is the broader science of biological diversity, including description, identification, nomenclature, classification and evolutionary relationships. Taxonomy is the practical discipline of naming, describing and classifying organisms. Classical taxonomy relies on morphology, anatomy, embryology and comparative anatomy, using herbarium sheets, museum specimens and dichotomous keys. Classical taxonomy can be constrained by convergent morphology and incomplete fossils, whereas molecular taxonomy can detect cryptic species and clarify deep relationships. Molecular taxonomy uses DNA and RNA sequences, PCR, RFLP, DNA barcoding and phylogenomics to infer relationships. Its tools include BLAST for sequence comparison, ClustalW for multiple sequence alignment, mitochondrial DNA for maternal lineages and ribosomal RNA sequencing for deep phylogenies. Thus, modern evolutionary biology integrates fossil hominid morphology, population-genetic principles and molecular systematics to explain how forms, gene frequencies and classifications change over time.