Evidence of Evolution Palaeontology Fossils Transitional forms Biogeography Selective environmental pressure Continental drift Comparative anatomy Homologous structures Vestigial structures Comparative embryology DNA sequencing

fossils A fossil is a remnant of a once living organism. It can either be a part of that organism or a trace that it left. Fossils are created by the dead organism or the trace it left being buried in sediment. Therefore, fossils are found in sedimentary rocks. Due to the way in which sedimentary rocks form, younger sedimentary rocks are found above older sedimentary rocks, assuming no geological upheavals have occurred. This means that younger fossils, as they were buried in younger sedimentary rock, are found above older fossils, as they were buried in older sedimentary rock.

fossils The oldest sedimentary rocks contain no fossils, as when the first sedimentary rocks formed the organisms on Earth were very soft and could not be fossilised. Older sedimentary rocks contain fossils of organisms that were simple and water living. Younger sedimentary rocks contains fossils of organisms that are more complex and both water and land living. This fossil record is in accordance to evolution, as all life came from the original single cell organism, shown through the simple eldest fossils. Then as evolution occurred, organisms varied, should through the more complex younger fossils.

Transitional forms Fossils have been found that appear to have the characteristics of two different groups of organisms that exist today. This shows how all organisms evolved from the same common ancestor. The archaeopteryx is an extinct organism that had a skeleton similar to theropod dinosaurs but had feathers and a wishbone. This shows common ancestry between reptiles and birds. The lobe-fin fish is the transitional form between fish and amphibians. Unlike fish, the lobe-fin fish had lungs, which a characteristic of amphibians. Fossils of amphibians similar to the lobe-fin fish have been found, but with larger rib, pelvis and limb bones, showing further evolution for support on land.

Selective environmental pressure Biogeography is the study of living things in relation to geographical regions. It shows how evolution occurs due to selective environmental pressure. Species living in different habitats close together are more similar to each other than species living in similar habitats far apart. This is because the single species living in a particular area evolves into others species to suit the different habitats within that area, due to the selective environmental pressure.

Continental drift Originally the Earth’s southern continents were part of one supercontinent called Gondwana. Today, several of these southern continents have a species of flightless bird. Each species is slightly different, but they are all very similar to each other. As they are flightless, they could not have flown from one southern continent to the others and then evolved. Instead, an original species of flightless bird existed on Gondwana, then when it split up the flightless birds on each new continent evolved to suit their new environment, creating the different species on each continent. The original flightless bird was a ratite. Today there is the: Ostrich in Africa Rhea in South America Emu in Australia Kiwi in New Zealand

Continental drift

Homologous structures Due to evolution, different species of organisms have similar body anatomy. This is because they all originated from the same common ancestor, and hence have similar body parts. The more alike two species are the more recent their common ancestor was. Homologous structures are similar structures in two organisms that are used to perform different tasks. These occur due to the structure staying with the organism during evolution, but slightly changing to suit its new task. An example is the leg of a dog and the flipper of a whale. Each has a different purpose, but they are similar and share traits due to their common underlying anatomy. Homologous structures are an example of a divergent evolution, where a number of species develop from one common ancestor due to having different selective environmental pressures.

Homologous structures Another example of a homologous structure is the pentadactayl limb which has five digits and is found in many organisms’ structures including human arms and dolphin fins.

Vestigial structures Vestigial structures are structures that an organism no longer uses but still has as a part of its body. This is because due to common ancestry different species have similar anatomy, but then due to evolution how they use their body parts changes. Hence, structures become unneeded. An example is the appendix in humans.

Comparative embryology The embryos of living things such as fish, humans, birds, turtles and rabbits all look extremely alike to each other. Due to evolution they have inherited similar stages of embryonic development from their common ancestor.

Dna sequencing All living things have DNA as they come from a common ancestor. In all organisms DNA has the same four base code. The more closely related a species is the more common their DNA sequencing is. When two new species evolve from a common ancestor their DNA slowly changes and becomes different. The number of differences in their DNA is proportional to the time since they separated.