Fossils as evidence for evolution

In a nutshell

Fossils are remnants of organisms that lived a very long time ago and they are often found in rocks. By comparing fossils of different ages, scientists can observe how organisms have changed over time. Fossils have provided evidence suggesting that humans have evolved from a common ancestor with apes.

Human ancestors

Humans and their ancestors are known as hominids. Fossil evidence of hominid species (1.) suggests that humans (2.) and chimpanzees (3.) evolved from a common ancestor about six million years ago.

Biology; Natural selection and genetic modification; KS4 Year 10; Fossils as evidence for evolution

Ardi

'Ardi' is the name given to the female fossil of the species Ardipithecus ramidus that is believed to have lived $4.4\ million\ years\ ago$ in Ethiopia. Scientists identified that Ardi had both human and ape features.

Ardi's feet were structured with a big toe that resembled an ape's. This suggested that she climbed trees. Her body structure more closely resembled an ape's as she had long arms and short legs. Her brain measurement was calculated using her 'cranial capacity' which is the space in the skull that is taken up by the brain. The size of her brain closely resembled that of a chimpanzee.

However, her leg structure indicated that she walked upright like a human not an ape. Her hand structure also showed that she did not use them to help her walk, which is a characteristic of apes.

Lucy

'Lucy' is the name given to the female fossil of the species Australopithecus afarensis that is believed to have lived $3.2\ million\ years\ ago$ in Ethiopia. Lucy also had human and ape features but hers more closely resembled human features than Ardi.

Lucy did not have the same ape-like big toe that Ardi had. Instead, she had arched feet that were better adapted for walking rather than climbing. Her arm and leg length was in between what you would expect for humans and apes and her leg bone structure suggested she walked upright better than Ardi. Lucy's brain was still similar to a chimpanzee's but was slightly bigger than Ardi's.

Leakey

Richard Leakey was a scientist who found many fossils of Australopithecus and Homo species in Kenya in the $1980s$ . He discovered Turkana Boy.

Turkana Boy

'Turkana Boy' is the name given to a $1.6\ million\ year$ old fossil skeleton of Homo erectus. He still had human and ape-like features but was more human-like than Lucy.

His leg and feet structure suggested he walked upright better than Lucy and he had short arms and long legs that more closely resembled a human than an ape. Turkana Boy also had a brain size similar to that of a human.

Timeline of human evolution

Comparing the fossils of Ardipithecus, Australopithecus and Homo have allowed scientists construct a timeline of human evolution.

Biology; Natural selection and genetic modification; KS4 Year 10; Fossils as evidence for evolution

Further evidence for human evolution

Homo species	Time	Tool
*Homo habilis*	$2.5-1.5\ million\ years\ ago$	They made simple pebble tools by hitting rocks together to make sharp fragments. They used these to crack bones open and scrape meat off bones.
*Homo erectus*	$2-0.3\ million\ years\ ago$	They used more complex tools like hand-axes that they made from sculpting rocks into simple shapes. They used these to hunt, dig and chop meat.
*Homo neanderthalensis*	$300,000-25,000\ years\ ago$	They used complex tools like wooden spears, flint tools and pointed tools.
*Homo sapiens*	$200,000\ years\ ago-present$	They still use flint tools. They also started to use pointed tools like arrowheads, fish hooks and needles around $50,000\ years\ ago.$

Note: Present day humans are Homo sapiens and we still exist!

Dating

Scientists use three techniques to find the ages of fossils and ancient stone.

Technique	Explanation
Looking at the structural features	Simpler tools will be older than complex tools.
Stratigraphy	This is the study of rock layers. The deeper the rock layer, the older it is. So fossils found deeper in the rock will be older.
$^{14}C$ dating	When stone tools are found they are often found with parts containing carbon, like a wooden handle. $^{14}C$ dating can be carried out to work out the age of the tool.

Biology; Natural selection and genetic modification; KS4 Year 10; Fossils as evidence for evolution

Biology; Natural selection and genetic modification; KS4 Year 10; Fossils as evidence for evolution