Missing Links Make Defining Species Possible

As we trace the ancestry of modern Homo sapiens backwards, there must come a time when the difference from living people is sufficiently great to deserve a different specific name, say Homo ergaster. Yet, every step of the way, individuals were presumably sufficiently similar to their parents and their children to be placed in the same species. Now we go back further, tracing the ancestry of Homo ergaster, and there must come a time when we reach individuals who are sufficiently different fro...

 Animals Evolved onto the Land and Took the Ocean With them

If you go back far enough, everything lived in the sea - watery, salty alma mater of all life. At various points in evolutionary history, enterprising individuals from many different animal groups moved out on to the land, sometimes eventually to the most parched deserts, taking their own private sea water with them in blood and cellular fluids. In addition to the reptiles, birds, mammals and insects we see all around us, other groups that have succeeded in making the great trek out of life's...