Original cartoon layouts
http://bancroft.berkeley.edu/Exhibits/Biotech/cartoon.html
Look at it and decide if it is suitable

I admit we had a number of the early editions floating around at University of Wash & Immunex when it first came out. It is well written and the cartoons catch a child’s interest. This book starts right from the beginning, and builds the topics carefully and simply but with a bit of wry humor all the way to why we have the human genome project.

Larry Gonick
http://en.wikipedia.org/wiki/Larry_Gonick
http://www.amazon.com/Larry-Gonick/e/B000AQ75IY/ref=ntt_dp_epwbk_0

This one: http://www.amazon.com/Evolution-Lets-Read-Science-Books/dp/0064450864/ref=cm_lmf_tit_27 looks a little “young” for your nephew (depends on, er, how smart he is), but it looks like it’s probably fairly comprehensive.

If he reads a bit above his grade level, http://www.amazon.com/Lava-Life-Universe-Sharing-Children/dp/1584690437/ref=cm_lmf_tit_6 might be a good one. It appears to be the second book in a series of (probably) 3, so you might want the whole set.

This series: http://www.amazon.com/Dawn-Life-Cartoon-History-Earth/dp/1553370813/ref=cm_lmf_tit_9 might be a little more… silly than your nephew likes, but you know him better than we do…

http://www.amazon.com/Life-Earth-Evolution-Steve-Jenkins/dp/0618164766/ref=cm_lmf_tit_14 looks pretty solid.

Another cartoony one: http://www.amazon.com/When-Sharks-Teeth-Began-Swarm/dp/142630546X/ref=cm_lmf_tit_15

This one’s human specific, but also looks like it has potential: http://www.amazon.com/Human-Body-How-We-Evolved/dp/0688067190/ref=cm_lmf_tit_25

If he likes whales, this one: http://www.amazon.com/How-Whales-Walked-Into-Sea/dp/0590898302/ref=cm_lmf_tit_30 might be good.

Our Family Tree is a good book:
http://www.amazon.com/Our-Family-Tree-Evolution-Story/dp/0152017720/ref=pd_sim_b_1