Natural selection as well as other factors determines how animals can evolve. Animals and plants are adapted to their environment. That means not all things are possible in evolution. If an animal or plant is not well adapted to its environment, it will be eliminated by natural selection. Therefore they cannot evolve in a way that make them less well adapted to their environment. Humans are adapted to living in the African savanna originally. Some of these adaptations include walking on 2 legs, a nearly hairless body, a big brain, and a five fingered hand that is unequaled in the animal world for its flexibility.
For most other living animals, walking on 2 legs is not adaptive. Birds do walk on 2 legs because it is adaptive to them. Are birds "half humans" according to your definition? or do they have to resemble us much more to be considered half human? So, it is possible for other animals to evolve to be similar to us. In fact, it is more correct to say that we evolved to be more similar to them, because birds have been walking on two legs while the dinosaurs roamed the earth but the ancestor of humans did not walk on two legs until about 4.5 million years ago It is therefore possible for some animals to evolve to be similar to humans. Scientists call it convergent evolution or simply convergence when animals or plants evolved to be similar independently of others. In fact there are many cases of remarkable convergent evolution in nature. For example, the thylacine or marsupial wolf is more closely related to kanagroos than they are to dogs, and dogs are more closely related to whales and dolphines. Yet the thylacine has evolved to be very similar to dogs, or more correctly, the grey wolf, which is the ancestor of domestic dogs The hyena, which is more closely related to cats than to dogs, nevertheless has evolved to be quite similar to wolves. therefore nature has shown us that it is possible for animals or plants to evolve to be similar to each other if they have a similar lifestyle.
Other remarkable examples of convergent evolution include whales and ichthyosaurs. Both of them resemble fish, even though whales are mammals and ichthyosaurs are extinct reptiles. even though it is possible to resemble one another, most animals look quite different because they are adapted to different niches (or ways to make a living). It is necessary for most animals to occupy different niches from one another because species with similar niches compete intensively for limited resources If all species eat the same thing for example, that thing will run out in a hurry. By adapting to different niches, organisms avoid competing against one another. In fact, it is the need to avoid competition that is the main reason why new species evolve. When a species of finch landed on the Galapagos Islands, it ate the same food as its ancestor in the mainland. But as time goes by, that food becomes scarcer since every bird ate the same food. By exploiting different kinds of food, new species of finches evolved. They evolved to be different so they can avoid competing with one another.
If anther species evolve to resemble us, then they will be competing against us. Therefore there is no reason for them to do that, if they live in the same area as we do. Further, even when a species finds it necessary to evolve a certain way, they often cannot because of what their body is made of. For example, a worm cannot evolve to walk on 2 legs because worms have no legs. neither do snakes .Therefore worms and snakes cannot evolve to be similar to humans. not all evolutionary paths are possible, because organisms are constrained by their past evolutionary history, and they are also constrained by luck, and by competition. Even though a lot of monkeys and apes can evolve to be like humans and walk on 2 legs, they do not because to them, walking on 2 legs make them much slower, and it gives them no benefit. In fact if a monkey or ape evolves leg bones similar to humans, they would have a hard time running on 4 legs. As a result they may be vulnerable to predators. they would likely be caught and eaten before they can pass along their genes
If it is so disadvantageous to walk on 2 legs, then why do humans do it. We did it because we evolved in the African savanna, and it was advantageous for us to walk on 2 legs because we needed to see danger from a distance before it can approach us, and it also allowed us to carry weapons to defend ourselves. Other animals, OTOH, may find a different solution to the same problem. Zebras for example are tall enough that they don't have to walk on 2 legs to spot danger, so they can simply keep running on 4 legs. They have no need to evolve to resemble us. In nature, don't fix what ain't broke is a rule that many organisms follow religiously. Scientists OTOH, has another fancier name for it. They call it Punctuated Equilibrium. Most species change little while they are alive, because there is no need to change. This is the equilibrium stage of a species' existence. When the environment changes, a small population of an existing species may change and change rapidly, and this is what they mean by punctuation.