What are the major reasons early Hominoids (apes) became Hominids (humans)?

Answer 1

There has been much speculation about what environmental conditions triggered the adaptations that led the hominid lineage towards bipedalism, sentience and humanity.

Unfortunately, it's not the kind of evidence that exactly fossilizes well, and so it's hard to actually prove any of the speculation.

We do know that bipedalism is one of the first adaptations seen on the branch that eventually leads to Homo sapiens sapiens. The earliest Australopithecines are essentially very chimp-like, but with a more upright stance. The development of this bipedal stance occurred through a process of accelerated hypermorphosis - essentially increasing the rate of body development and maturity while maintaining the bipedal stance of the juvenile apes (as seen in modern chimpanzee juveniles). Thus, it was not a unique mutation, but a selection of existing variation - something even geneticists tend to forget.

Why bipedalism was an advantage to those early Australopithecines is the big question. The bipedal ape has better use of its hands, to carry, hold, manipulate and investigate with. Perhaps the Australopithecines were already increasing their tool using abilities, and the free hands were an advantage in making and carrying those tools.

There are no stone tools associated with these early Australopithecines, but they may have utilized what is known as an osteodontokeratic technology (literally translates as 'bones, teeth and horns') - using sticks, and the remains of dead animals as tools. Perhaps they used these tools to hunt and kill other animals, and then used the dead animals to make more tools.

This hunting hypothesis is a favourite of many paleoanthropologists, as it provides sort of a continuous feedback selection process - the better hunters kill more animals, getting better material to make better weapons, and kill more animals, and so on. It can also be used to explain other human developments, such as communication (hunting bands cooperating to kill larger animals), family bonds and sexual segregation of roles (male hunters, female gatherers), as well as being sexy as a speculative exercise (the idea of killer apes developing sentience through their bloodthirsty ways sells more books). The higher nutritional content of a meat diet also explains where the hominids get the energy to devote to increased brain power - which provides better hunting, which gives a better diet, and so on again.

Others have argued for other scenarios. Today, many of the other critters with high manual dexterity (raccoons, sea otters, yapok) use their agile digits to search through muddy water and dirt to pick out tasty morsels from aquatic habitats. Sifting around in search of clams, shrimps, crayfish and other goodies takes both manual dexterity and a fair bit of intelligence. If those early hominids could swim, they'd be even more efficient. Today, we are amongst the only primates that can swim, and we're definitely the best at (for primates). Our nose is shaped to keep water out while swimming, and it would also explain our reduced body hair thickness. Even baby humans take readily to water, and our proclivities towards enjoying beaches and seafood may also be tell-tale signs. This is another neat little theory, with the drawback of having no real fossil evidence to support it. But coastlines are amongst the worst places for fossilization to occur.

There are other theories out there (including some really speculative ones, like aliens came and manipulated the apes to become more human), but these are probably the two biggies.

Answer 2

The Aquatic Ape hypothesis has been around for a long time now and I still have difficulties with it. I agree it is almost certain that ealy hominids would have lived near water and would have used resources such as shellfish but I disagree that we evolved characteristics that favoured a marine existence.

To me, the hooded nose is a direct result of bipedalisn - it keeps the rain out when you are standing upright. It conveys no real advantage to a swimmer. The lack of hair is another bit of selective reasoning. I agree that whales lack hair but just about all the rest of the marine mammals don't. Seals, sea lions, otters, platypuses, desmans and the rest all have hairy or furry coats which assist in streamlining. Human hair doesn't do this which is why competitive swimmers shave it off.

Each of the characteristics cited in the Aquatic Ape theory can be dealt with similarly - there are other reasons for them or they are selective. It might be that there was an aquatic phase in human development but I want to see a lot more evidence and more convincing evidence than has been presented so far.

My opinion is that bipedalism and the freeing of the hands is the defining characteristic of the line that led to modern humans. Not all the bipedal hominids made it, various branches came to an evolutionary dead end, but one did and that's us.

Answer 3

Apes didnt become humans. They are not related.

Answer 4

they didn't
don't believe Darwin
otherwise why all apes didn't become humans