Human Evolution - Physiological

Humans evolved from the great ape family, also known as Hominid, which lived on Earth about 20 million years ago. Until relatively modern times there were a number of different human species, some of which coexisted with our own Homo sapiens. 

A tree is often used to represent lineage. Around 7 million years ago humans and chimpanzees shared a common ancestor. Over time, different evolutionary traits were developed, leading to different human species. Evolutionary biologists currently recognize 7–12 distinct human species. 

Widely considered to be the earliest human species, habilis evolved around 2.4 million years ago. Habilis ate meat, which increased their brain size tremendously, and is believed to be the first species to start cooking food.

At an average height of 6 feet, heidelbergensis was taller and more muscular than the modern human species. Heidelbergensis was crafting spears long before contemporary humans and evidence suggests they were the first species to bury their dead.

Some evolutionary biologists believe that Homo erectus was the first human species to master open water travel, a huge feat for a species existing 130,000 years ago. Erectus appeared to go extinct only 27,000 years ago.

Indonesian legends talk of tiny, cave dwelling people. People assumed they were fantasy until the discovery of tiny human fossils in 2003. Named Homo floresiensis, this species remains controversial. Evidence suggests these diminutive humans used tools and harnessed fire long be

Neanderthals went extinct around 40,000 years ago. DNA analysis shows that 2.5% of today's human population contains neanderthalensis genes, meaning they lived alongside modern humans and bred with them. Evidence tells us that Neanderthals built shelters, wore clothes, and made tools.

Originating in Africa and around for 200,000 years, Homo sapiens survived when all other human species became extinct. Some evolutionary biologists believe their survival was because of diet. Sapiens hunted all types of prey while other human species were more limited.

Modern–day humans, known as the species Homo sapiens, originated in Africa. Through the use of DNA analysis, scientists have discovered that this species of human began to migrate to other parts of the world around 100,000 years ago.

Currently the most accepted theory about where Homo sapiens originated states that it began in Africa. The oldest sapien fossils have been found in Ethiopia, however fossils found in the Middle East cast doubt on this theory.

About 50,000 years ago something changed and Homo sapiens started migrating in earnest. The first wave of modern humans traveled as far as Australia and Australian Aboriginals are direct descendants of these early sea explorers. 

Genetic evidence suggests that Homo sapiens almost became extinct just before leaving Africa. Some evolutionary biologists believe that the entire human population was under 10,000, about the same number of cheetahs found in the wild today. We were extremely lucky to make it!

Around 20,000 years ago Earth was in a time period called the Last Glacial Maximum, with glaciers and cold climate. Ice sheets covered most of North America, northern Europe, and Asia. Sea levels were much lower due to water being locked into the glaciers.  

During Last Glacial Maximum a small group of sapiens set out from Asia. They were able to cross a giant land bridge into the Americas as the sea level was almost 330 feet lower than it is today.  

Homo sapiens have changed greatly from when we first emerged out of Africa some 200,000 years ago. Many of our evolutionary traits help us survive the changing world. However, evolution doesn’t stop. As a species we are also continuing to evolve.

This is a recreation of a fossil that was found in Herto, Ethiopia, and scientists believe the fossil is 160,000 years old. It represents the earliest example of the Homo sapiens species found so far. 

Modern Homo sapiens are smaller and lighter. This trend extends to the skull as well as brain size. Although modern human’s brains are the smallest they have ever been, they are larger compared to body size than in other species, such as Homo neanderthalensis.

Today, human jaws are much smaller than those of early Homo sapiens. For this reason, some people need to have their wisdom teeth removed, as their jaws are too small to accommodate the number of teeth humans originally evolved. 

Humans now vary widely in appearance. The first Homo sapiens all looked very similar but as they spread across the world, this changed. Each population’s appearance slowly adapted to the challenges of their environment, leading to the wide range of races we see today. 

DNA evidence suggests that blue eyes originated from a single person living around 7,000–10,000 years ago near Romania. This means that every human alive today with blue eyes is a distant (very distant!) relative to this original person.

DNA evidence suggests that Homo sapiens were dark–skinned until 10,000 years ago. It is believed that lighter skin evolved to absorb a higher amount of vitamin D from the sun, in places like northern Europe during winter. 

To arrive where we are today took over 200,000 years. Evolutionary biologists have uncovered major stepping stones in our evolutionary journey, starting from when the earliest human species evolved to walk upright.

The earliest evidence of humans walking on 2 legs dates to 3.7 million years ago. It is suggested that at that time humans both walked on 2 legs and were still agile tree climbers, however they were unable to run.

Humans lost their fur, but then evolved hair in its place. Evolutionary biologists are still unsure as to why humans lost their fur covering, as most of the other savanna animals have retained their fur throughout their evolutionary journey. 

Human bone structure suggests the mastery of endurance hunting. This practice involved slowly stalking and tracking prey for hours at a time in the hot African sun until the prey became too exhausted to resist the predator.

The Earth’s climate has changed constantly over its history. There have been periods much colder than today and long periods of time that have been much warmer. 

New theories discuss the possibility that milestones in human evolution were achieved due to a change in the Earth’s climate. All the following ideas are still just that, ideas put forth by some evolutionary biologists who are still collecting evidence to support their ideas.

Around 3 million years ago Earth’s climate became warmer and drier, causing African forests to disappear. Our ancestors adapted to the new habitat called savanna: hot, dry grassland with sparse trees. In order to adapt, the earliest hominids began to walk on 2 legs.

Climate data suggests that many of the major advancements made by humans occurred around the time of significant climate change. For example, stone tool technology changed drastically during times of climate variability and humans brains grew rapidly. 

Some evolutionary biologists theorize humans migrated during times of climate uncertainty, with these populations adapting to new environments. Other biologists suggest that populations adapted to climate change first, and then migrated to new areas, bringing new technology.

It seems cold in particular helped humans evolve. Due to the scarcity of plant life humans needed to find other food sources, often meat, which directly led to increased brain growth. Innovations included controlling fire and developing complex hunting tools and clothing.

Paleoanthropology is the study of human evolution. Paleoanthropologists, or evolutionary biologists collect data on ancient humans to create timelines of events. 

Modern–day evolutionary biologists use cutting edge technology to obtain data about ancient humans, making this field an evolving field of study.

As expected, evolutionary biologists gain the most information from fossils of ancient humans. These fossils become uncovered due to construction or weather, and provide a wealth of data for biologists to analyze. Tools, ancient fire pits, and rubbish piles also give valuable clues.

Once evidence is removed from the ground, technology steps in. Studying tooth enamel under an electron microscope can reveal the diet of an ancient human. Mitochondrial DNA analysis can show where the human migrated from and whether they are an ancestor of a population group today.

Recent breakthroughs in technology has allowed DNA to be extracted from bone matter, revolutionizing the way human evolution is studied. Biologists use this information to track migrations of people, identify individuals, and trace genetic mutations such as blue eyes. 

Thanks to forensic technology, evolutionary biologists can reconstruct what ancient humans looked like based on their bone structure. Also called forensic anthropology, analyzing human remains for the purpose of establishing identity usually focuses on the skeleton.