Fossils Fossils are the remnants or traces of an organism that once lived on earth. Fossils may include parts of organisms or the traces they left e.g. footprints. The parts of organisms that are usually preserved are the ‘hard parts’ such as bones or shells. The ‘soft parts’ of an organism are usually decayed and decomposed by bacteria. Fossils can also be preserved in amber or be formed by petrification.
Fossils are usually found in sedimentary rocks • Age of rocks can be determined by using radioactive dating and by correlating the fossils found in them with rocks of known age. • Relative age of rocks – assumption that younger rocks are situated on top of older rocks, which infers that older rocks must contain older fossils. • The theory of evolution is clear because the more recent the rock, the more complex the structure of an organism
Biogeography Biogeography is the study of living things in relation to its geographical regions. Darwin and Wallace used biogeography as strong evidence of evolution. They observed species living in the same area had more similarities than species living in similar habitats far apart. They concluded that species evolved due to selective pressure in their own habitats.
Comparative Anatomy The comparison of the anatomies of different species looks for evidence of evolution from a common ancestor. Homologous structures: • Found in plants and animals • Have the same origin but not exactly the same function • Example of divergent evolution (species from one ancestor, becoming less alike due to habitat differences) • Example: pentadactyl limbs (limbs with 5 digits) of vertebrate animals – same structural plan from common ancestor but have altered to suit different environments
Comparative Embryology Comparative embryology is a branch of embryology that studies the comparison between embryos of different species. The embryos of organisms all looked the same which shows that we are from a common ancestor.
Comparative DNA DNA and the proteins it produces can provide evidence about evolution. If 2 new species evolve from 1 common ancestor, their protein molecules and DNA change and become different due to separation. The amount of differences is proportional to the time since separation. It shows us how related the species are depending on how similar the DNA sequence is.