Here is a Google n-gram of the word "transhumanism", all the hype that exists today as shown in that particular graph is a result of the hypothesis that neurons are similar to transistors, and that the total capacity of the brain is that of 100 billion neuron-transistors, and 100 trillion synpases.[1] At the moment the total computation ever produced is approaching the equivalent of that, and that is the reason why you see a spread of the meme "transhumanism" - if that hypothesis were true, you would see AGI transcend human beings very soon, that is why the idea itself is powerful, and has captivated the attention of many people.
Tubulin as molecular switches
Look at these here. This is binary representation of bytes on a microtubule, with a perfect fit to CAMKII, a kinase that has been correlated with long term memory since 3-4 decades.[2] Most people are not aware of that. The model below is my adaptation of Craddock, Tuszynski and Hameroff's work from 2012.[3]
Neurons are around 0.01 mm in size. That is the size of a transistor in the 1960s, see this chart (logarithmic scale. )
Tubulin are 4.5 x 8 nano meter, so a nano-scale computer. The idea that biology would use a computer with transistors (neurons) 1000x the size of 14nm transistors that have been pretty common in human-built computers, is, well, how does that add up exactly?
Here is a size comparison, very huge neurons at 10 micron, and tubulin dimers that are close in size to the smallest transistors ever created. Neurons are more similar to integrated circuits, filled with billions of transistors (tubulin dimers organized in microtubules) per neuron, and then "pins" (synapses) to talk to other neurons.
Memes that spread through genetic bias
The memes that are loudest in ordering genes to replicate them have a survival advantage, and similar to the Abrahamitic religions story of heaven and hell, eternal life and eternal damnation, "transhumanism" propagates via the limbic system, mostly subconscious processes, and followers see both immortality and omnipotent control as potential rewards from their belief.
When facing a contradiction, check your premises
Take the line "to transcend our species capacity is what makes us human, therefore we are transhuman", that is a contradiction. The first half says that the definition of human is to transcend its own condition, the second half then says "therefore we redefine it". "transprimate" is a more accurate word, since apparently as you can see, humans are "trans-primates", that transcend their species capacity with every new technology.
The rejection of the human condition as a bias
Clearly, there is exponential rates of evolution of technology (as a result of that each generation of technology builds on the previous, note that the same is also true for biology), the false narrative is not that but certain assumptions of the human condition, that underestimate it, primarily by underestimating the complexity of the human brain and also of biology and nature overall.
"transhumanism" as "technological escapism"
George Gilder describes "transhumanism" as escapism, a fight and flight symptom, a form of substitute for the lack of a legal system for the digital age, among other things, which I think is very accurate (I fell for the hype myself for a few years, very much for exactly those reasons. )