Can someone from the science side of Tumblr explain this?
Basically this argument uses a flawed understanding of (i) the process of evolution and (ii) the evolution of humans and other apes.
What you have to understand is that evolution does not mean that every individual of species A turns into species B over time, without any individuals of species A persisting - this is transmutation and, while it does occasionally happen, it is not the main mechanism of evolution. Rather, evolution works by gradual mutation and selection acting over time, such that species A at time 0 can give rise to species B at time N. It is possible for species B to arise from species A without species A having ever gone extinct - when this happens without any gene flow between the two populations, usually in some kind of geographic isolation, we call this ‘allopatric speciation’. It is equally possible for species A to give rise to species B and species C, while at the same time going extinct itself.
This means that if you trace lineages backward through time, they converge. Each convergence is the point where the two lineages have a common ancestor. The most recent common ancestor (mrca) of a set of lineages is the most recent point at which all lineages were the same species.
Chimps, Gorillas, and other apes, are not our ancestors. Rather, they are other lineages that diverged from a common ancestor of our group. That common ancestor was an ape, but it was not an ape that is still around today.
I hope that helped. If you have more questions, don’t hesitate to ask.
On behalf of the Science Side of Tumblr.