From the second link...
Australopithecus ramidus (mid-Pliocene, 4.4 Ma) -- A recently discovered very early hominid (or early chimp?), from just after the split with the apes. Not well known. Possibly bipedal (only the skull was found). Teeth both apelike and humanlike; one baby tooth is very chimp-like. (White et al., 1994; Wood 1994)
Australopithecus afarensis (late Pliocene, 3.9 Ma) -- Some excellent fossils ("Lucy", etc.) make clear that this was fully bipedal and definitely a hominid. But it was an extremely ape-like hominid; only four feet tall, still had an ape-sized brain of just 375-500 cc (finally answering the question of which came first, large brain or bipedality) and ape-like teeth. This lineage gradually split into a husky large-toothed lineage and a more slender, smaller- toothed lineage. The husky lineage (A. robustus, A. boisei) eventually went extinct.
Australopithecus africanus (later Pliocene, 3.0 Ma) -- The more slender lineage. Up to five feet tall, with slightly larger brain (430-550 cc) and smaller incisors. Teeth gradually became more and more like Homo teeth. These hominds are almost perfect ape- human intermediates, and it's now pretty clear that the slender australopithecines led to the first Homo species.
Homo habilis (latest Pliocene/earliest Pleistocene, 2.5 Ma) -- Straddles the boundary between australopithecines and humans, such that it's sometimes lumped with the australopithecines. About five feet tall, face still primitive but projects less, molars smaller. Brain 500-800 cc, overlapping australopithecines at the low end and and early Homo erectus at the high end. Capable of rudimentary speech? First clumsy stone tools.
Homo erectus (incl. "Java Man", "Peking Man", "Heidelberg Man"; Pleist., 1.8 Ma) -- Looking much more human now with a brain of 775-1225 cc, but still has thick brow ridges & no chin. Spread out of Africa & across Europe and Asia. Good tools, first fire.
Archaic Homo sapiens (Pleistocene, 500,000 yrs ago) -- These first primitive humans were perfectly intermediate between H. erectus and modern humans, with a brain of 1200 cc and less robust skeleton & teeth. Over the next 300,000 years, brain gradually increased, molars got still smaller, skeleton less muscular. Clearly arose from H erectus, but there are continuing arguments about where this happened.
One famous offshoot group, the Neandertals, developed in Europe 125,000 years ago. They are considered to be the same species as us, but a different subspecies, H. sapiens neandertalensis. They were more muscular, with a slightly larger brain of 1450 cc, a distinctive brow ridge, and differently shaped throat (possibly limiting their language?). They are known to have buried their dead.
H. sapiens sapiens (incl. "Cro-magnons"; late Pleist., 40,000 yrs ago) -- All modern humans. Average brain size 1350 cc. In Europe, gradually supplanted the Neanderthals.
What I see here are distinctions made on the basis of height, brain size, teeth size, build, etc.
Are these distinctions not simply possible between different human beings?