Let's take a closer look at the hominin skulls in the Senckenberg Museum's human evolution room. Keep in mind this is not a linear progression through our ancestors, and more like a bunch of closer and more distant cousins.
The first one, Sahelanthropus tchadensis is seven million years old, and may very well not be a hominin at all. I've always leaned towards the hypothesis that it's a gorilla relative, not one of ours. No matter which branch of the apes it belongs to, it lived not long after the time the human-line (hominins) and the chimp-line separated, and possibly even before that point!
Ardipithecus ramidus, the first hominin from where we can start making a fairly decent family tree of our relatives. Before this point, 5 million years ago, hominin fossils are very rare, fragmentary, and difficult to assign. One of the most interesting things that does seem to emerge from these early fossils is that we have walked on two legs for a long time. Maybe even so long that our common ancestor with the chimps and bonobos did it!
Lucy represents Australopithecus afarensis, who shows up at this point (3.3 million years ago).
Australopithecus africanus, the Taung child to be precise. We're about 2.8 million years ago at this point. Australopithecines must've been such fascinating creatures.
Homo habilis, the 'handy man', named that way because when they were discovered they were thought to be the first humans who used tools. Since then, Australopithecus tools have been found, and tool use by many different animals has also been documented.
Homo rudolfensis, a population of humans who lived at the same time as Homo habilis and were notably bigger and a little brainier. Does it warrant being its own species? That depends who you ask. Splitting vs lumping is a point of contention in almost every group's biology, and it can run especially high in the field of human evolution since hominins are A very high profile and important fossils that directly relate to our own origins, and B an extremely tangled group that seems to have produced loads and loads of isolated populations and subspecies that regularly migrated all over the place and had frequent interbreeding events. Personally I tend to come down on the side of lumping them into a few major species.
Paranthropus boisei. These were basically a separate lineage of australopithecines, quite different from our own ancestors, who continued to do australopithecus things until quite recently. They were very good climbers and seem to have returned to the trees.
Homo ergaster, either a close relative or a synonym of the more famous Homo erectus. This is the point where we got really brainy, probably figured out how to make fire ourselves, and spread from Africa to Eurasia.
Homo heidelbergensis. Homo erectus and its many subspecies spread all over Africa and Eurasia and existed for well over a million years. As time marches on and evolution did its thing, we eventually start calling the ones in Africa Homo heidelbergensis. They were quite tall, positively enormous compared to little Lucy a few million years back, and they too joined in the human migrations out of Africa. From the H. heidelbergensis who moved into Eurasia we eventually get neanderthals and denisovans, while Homo sapiens evolved from the heidelbergensis populations in Africa.
And there's the neanderthals! Large-brained and creative (the first known cave paintings belong to them and they buried their dead), they were likely quite different from the brutish image we often get from them. Rather than truly dying out, their populations eventually merged with the larger Homo sapiens population once they migrated out of Africa, leaving our modern genes with a couple percent neanderthal DNA.
Homo sapiens. And that's us! Not so much the last remaining branch of the human family tree as much as several of the separate branches ended up coming back together and weaving into a single bigger branch.
And then there's these little guys, Homo floresiensis! Probably originating from a Homo erectus population that ended up on the island Flores, insular dwarfism ended up making them grow quite tiny. On their isolated island, they remained until about 50000 years ago.
