Expert: Christopher Rosch - 1/16/2006

Question
Hi, I'm Kyle Costigan and I was wondering if you could answer a few questions for me. I'm doing a science fair for Lake Denoon Middle School, Wisconsin. My title, for my project, is “How we are who we are.” It tries to describe how we evolved from the very beginning of hominids. I'd really appreciate it if you gave me as much information as you're willing to give. I need to interview a professional in order to get an A so I'd really appreciate and help you could give me.


Q: How long ago did we start to branch off from our ancestors?

A: (Please fill outJ)


Q: How many different type of species have we gone through to get to our current form?

A: (Please fill out)


Q: Why are we so unique compared to every other species?

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Q: What do you think was our most beneficial moment for out species?

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Q: Why did we keep evolving? Why did we keep genetically mutating into different species?


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  Thank you for everything you may have filled out very much and any info you give me will help me a lot.

                             Thanks again,
                                Kyle Costigan


Answer
Q: How long ago did we start to branch off from our ancestors?

A: Recently, with the discovery of new hominid species like Sahelanthropus tchadensis and Orrorin tugenensis, the branching of the 'ape' and 'human' lines of evolution had to be placed some 6 or even 7 million years ago. The genus Homo -- which includes Neanderthals and the modern human, Homo sapiens -- evolved about 2 million years ago.


Q: How many different type of species have we gone through to get to our current form?

A: Difficult to answer, because the 'family tree' of humans is uncertain yet. But, since the branching from the ape line, at least six to eight hominid species existed which were direct ancestors of humans.
The probably earliest hominid after the separation of 'apes' and 'humans' (at least 6 million years ago) was Sahelanthropus tchadensis. It was followed by Orrorin tugenensis and Ardipithecus ramidus. The first Australopithecus species, A. anamensis, evolved about 4 million years ago. Australopithecus afarensis or its descendent, A. africanus, may be the direct ancestor of humans. The first species of the genus Homo was Homo habilis which probably evolved into Homo heidelbergensis and, later, into Homo sapiens.
The major difficulty in reconstructing a family tree for humans lies in the sheer number of different hominid species which existed in the last few million years -- and the expectedly high number of species yet missing from the fossil record.
At any given time usually three to four species existed contemporarily. For example, three million years ago Paranthropus, Kenyanthropus and two or more Australopithecus species (A. africanus and A. garhi) existed at the same time, but only one Australopithecus species (probably A. garhi) eventually evolved into the ancestor of humans - all other lineages became extinct in the next million years.


Q: Why are we so unique compared to every other species?

A: Because humans have self-awareness and the ability to communicate in abstract symbols (see next answer).


Q: What do you think was our most beneficial moment for our species?

A: the moment, the capability for symbolic and abstract thinking evolved. This was a prerequisite for the development of self-awareness as well as all we call "culture" (in the conservative sense; today, we know that certain animals like chimps have rudimentary cultures as well). Perhaps the most important direct consequence was the development of languages by which group members could be informed about events in the past (important for traditions and cultural memory) or something they did not experience themselves, especially thoughts and emotions.


Q: Why did we keep evolving? Why did we keep genetically mutating into different species?

A: Evolution is never finished because mutations naturally happen to occur; evolution does not work goal-oriented and modern humans are certainly not the peak of evolution. Because of mutations whole populations (of humans, animals or plants) gradually change until they evolve into a new species. Static populations would not survive in an ever-changing environment (think of climate changes) which enforces constant adaptations.


For more information see
http://en.wikipedia.org/wiki/Evolution_of_Homo_sapiens
But be aware that the family tree shown there is just as hypothetical as any other. As opposed to true genealogies you will note that the connections between different species are missing in the Wikipedia figure. The information we have today is simply not sufficient to produce reliable trees for the evolution of hominids.

If you want to extend your research, I highly recommend the Scientific American magazine (local library). Admittedly, the articles are too complicated for middle school, but the illustrations are very good (if you need some for your project) and - since the articles are written by experts in their respective fields - they are alway up-to-date. If you are interested I'll send you a complete PDF issue on human evolution (about 3.9 MB; chris.roesch@trefid.net)

Good luck with your project! Best regards,
Christopher


PS: please apologize mistakes in spelling and grammar - I'm not a native English speaker.