Humans: where we have been and where are we going

By Gloria Lima

When looking at how humans have change throughout the year one may simply think in the past hundred years or maybe even a bit further to medieval times or to ancient Rome and Greece. But nonetheless, humans have been around for longer than that– try around 100,000 years! To understand the idea that human ancestors may have been around longer than today’s humans have though is a bit mind blowing.  To think that we have been on this earth for that long is pretty amazing. 

But how was this found? How can we know that humans have lived that long and if we do know they have lived that long how did we get to where we are now? There are many theories about this, and there are many possible reasons we may have traveled to new regions, like climate change, overpopulation in an area, or simply the joy of exploration. No matter which option our early ancestors picked, we know that they  migrated from Africa as can be seen in Figure 1.

800px-Spreading_homo_sapiens

Fig. 1) Pathways of human migration out of Africa. From Wikimedia Commons.

Since at least 100,000 years ago, early humans have been moving outward to different areas of the world. As they moved upward to northern Africa there is evidence for a founder effect on the population as some people moved west and others moved on to the Middle East. The reasons may have been who was better suited for the environment or simply preference for one habitat or another. In Fig. 1, it is possible to see the path that our ancestors have taken and to also see where it had split into different areas of the continents such as Asia, Europe, and later North and South America. But how exactly did humans get to the America’s if it is secluded today by water? At the end of the last ice age, sea level was much lower, and so there was a connection between northern Russia and Alaska where today his is because there is a shallow body of water called the Bering Strait.

The connection between Russia and Alaska was formed at the end of the Pleistocene time period, 21,000 years ago. During this time, large areas of land were covered in ice and many animals adapted to ice age climates roamed the earth, including  woolly mammoths, saber-tooth cats, and giant sloths. Many these mammals were better suited for living in cooler climates, but where do humans  fit in? Humans are known being very adaptable– we’re  able to adjust our environments for their own benefit. For example, Homo erectus (an early ancestor of humans that lived until about 143,000 years ago), made stone tools to manipulate their environments, though there isn’t evidence that they used fire extensively or built shelters.

During the last ice age, there were two surviving descendents of Homo erectusHomo sapiens (us modern humans today) and Homo Neanderthals (a close cousin). When looking at the two, it can be seen that there is only a slight difference between us; Neanderthals were more muscular, their remains are found in cooler climates. Why did Neanderthals disappear? Was it climate change? There was an  period of time in which both Neanderthals and modern humans co-existed, between 45,000 and 27,000 years ago. After 27,000 BP, only modern humans remained. Yet Neanderthals were around during the middle to near end of the Pleistocene, which means that they would have dealt with the fluctuations from cooler, glacial temperatures to warmer interglacials.

625px-Geologic_Clock_with_events_and_periods

Geologic timescale represented as a clock, with events and periods indicated. The first homonids evolved around 2 million years ago, which is very recent in geologic time. Wikimedia Commons.

What does this all mean for modern day humans? Well for one, we as Homo sapiens have been around for a short amount of time compared to many other animals and organisms– including our early human cousins! As seen in Fig. 2, the Pleistocene period is only a sliver of the overall time that organisms have been on this earth. Yet to us modern humans, it can feel like we’ve been here for a very long time– so much has changed even from ancient Rome to medieval Europe, to the first European colonists in United States, to today. As we move closer to modern times it easy to forget how long ago modern humans came to be.

How did we figure all this out? There are many ways to date artifacts nowadays. A common method is radiocarbon dating, which is measures how much of the radioactive carbon isotope (carbon-14) is left in a artifact. Living things accumulate carbon-14 until they die, and then this radioactive element breaks down through time. If you measure the amount in an artifact, you can back-calculate the time since death using the isotope’s half life.

Of course, the age of writing (since about 4000 BC) has made dating events much easier, and we can even see changes in how people thought, how they saw the world around them and how they interacted with one another. Writing also provides clues to tell how they survived in their environment with other animals and organism (as disease and bacteria). By comparing the past to the 21st century and see how humans have changed throughout time. In a short geologic time, we’ve gone from making rudimentary stone tools to colonizing new lands to fighting wars with other groups of humans to now, in many places, moving toward the equality of all people. When we see how we has modern day Homo sapiens have progressed in a short amount of time, it is amazing to realize how much we have accomplished– even though it doesn’t seem like a short amount of time compared with our own lifespans. Who actually knows where modern day humans will go from here? While it may seem as though humans have been on Earth for such a long time, the truth is we are just starting out.

Reference:

  • WHAT’S NEW. “Encyclopedia> Radio carbon dating.”
  • Geologic Time.” The American Heritage Science Dictionary. Boston: Houghton Mifflin, 2011. Credo Reference. Web. 3 February 2014.
  • Fernandes, C. A., Rohling, E. J. and Siddall, M. (2006), Absence of post-Miocene Red Sea land bridges: biogeographic implications. Journal of Biogeography, 33: 961–966. doi: 10.1111/j.1365-2699.2006.01478.x
  • Perspective – Biological Sciences – Evolution: Brenna M. Henn, L. L. Cavalli-Sforza, and Marcus W. Feldman.The great human expansionPNAS 2012 109 (44) 17758-17764; published ahead of print October 17, 2012,doi:10.1073/pnas.1212380109
  • Hopkins, David. The Bering Land Bridge . Stanford, California : Stanford University Press, 1967. 1-13. eBook.
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3 thoughts on “Humans: where we have been and where are we going

  1. It sounds like you’ve got the Deep Time bug — me, too! I’ve always wondered what drove people to make the choices they did, and what it was like to migrate to a completely new continent. I just imagine the first humans making it to North America, and experiencing totally new landscapes, plants, and animals, all for the first time. Some things would have been familiar, and others utterly new.

  2. Figure 2 is absolutely incredible! It really shows how short of a time humans have been on Earth. I think people often get overwhelmed when dealing with time-spans of millions or billions of years, and so they just brush everything aside as “a really long time ago.” This figure is really helpful if large time-scales are too complicated or unfamiliar to deal with.

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