There is variation among individuals of the same species, and therefore differential survival, with survival of only the fittest. • Human variation E.g. darker skin at the equator is a function of increased melanin in the skin for protection against the sun (environmental adaptation). Pale skin is an environmental adaptation to reduced sunlight at higher latitudes. Less melanin allows the sun in because sunlight promotes the production of vitamin D. Human variation E.g. Oriental eyes are genetic, due to a relatively isolated gene pool (breeding population) in the past 120 000 years in the East. Lions Panthera leo Lions (Panthera leo) only mate with lions, and that makes them one species. They do not mate with other cats like tigers, leopards and panthers. Tiger Panthera tigris Leopard Panthera pardus Panther Puma concolor Genus: Equus Equus zebra (mountain zebra) Equus quagga (common zebra) Equus africanus (wild ass) All of the horse type, thus the genus Equus, but different enough to be divided into species. Equus zebra Equus quagga Equus africanus Genus Equus Zebras do not mate with race horses. Different species cannot produce viable offspring if mated. e.g. a mule is a cross between a donkey (species) and a horse (species). A mule is always sterile and cannot reproduce. 2. This infers a struggle for survival and competition between individuals of the same species. 4. There is a natural selection for individuals with traits favoured in a particular environment. 5. Traits are in the genes, so are inherited through sexual reproduction (male and female genes paired). • New genetic combinations allow for variation, giving more chances to adapt to a changing environment. 6. Offspring carry the advantageous feature and pass it on to their offspring. The result is a gradual genetic shift (evolutionary change) in the population as the trait is naturally selected. e.g. better thermo-regulation in some lions living in extremely hot desert environments Genes are not the only factor that determine an organism’s appearance. • Environmental influences: A person with a dominant gene for height could end up short due to poor diet and living conditions. • Mutation: random change in an individual’s genes. E.g. of a useful mutation: A lamb born with short, bent legs that prevented it from jumping fences. Used in breeding to establish short-legged sheep.
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