The Human Body: The Amazing Multitudinous Dichotomy

Question from Robert:
Message: To whom it may concern: How can you explain the amazing complexity of human beings? The average human body has between 75 to 100 trillion cells. If no God, how could trillions of cells, which have no brain, collect themselves together and then change into all the highly specialized cells of the human body?

Also it takes a man and woman to create a baby. Therefore, a male and female body would have had to evolve at exactly the same time~! And a hermaphroditic human being still poses the same problem. The male and female parts would have needed to evolve — AT THE SAME EXACT TIME~! That is absolutely impossible.

Answer by SmartLX:
Didn’t actually go looking for answers to these, did you? You immediately took them to be ideal rhetorical blunt objects to beat any “Darwinist” into silence. The second one isn’t even a question, and you claim it’s impossible; this is not the language of someone who genuinely wants to know. Even if there were no answers to either one, to assume that there is no possible explanation without actually ruling any out is an argument from ignorance. Thing is, there are quite reasonable answers to each.

Today there are plenty of living things with no brain, and they assemble themselves just fine. Even the creatures with brains must start their self-assembly before the brain is formed, so brains have little or nothing to do with it. One cell automatically divides into two, then four, then eight and so on, held together with membranes. The DNA contained in each and shared by all contains the necessary information to allow each of these “stem cells” to metamorphose into a skin cell, a brain cell, a liver cell or whatever is needed. The cells can send biochemical signals to each other, so for example a cell is informed that there are enough lung cells for the moment and it becomes a bone cell instead. Once enough of an organ has come together, it reflexively begins its specific function: the brain manipulates electrical energy, the kidneys process liquids, the bones produce blood cells.

As for why there are so many cells in a body, there are many factors that limit the size of a living thing but for us none of them really kick in until the trillions. There’s enough food to feed them, they’re light enough not to collapse under their own weight, they’re strong enough not to break apart without significant force. There are obvious advantages of having so many of them together, too: they can defend themselves against similarly large threats, huge numbers of cells can be cut away or killed while the rest survive, they can reproduce fast enough to replace short-lived cells like skin cells. Once early single-celled organisms first fused together and shared their DNA about one billion years ago, there was nothing to stop them from amassing more and more cells per organism for all that time. Exponential growth has led to the huge conglomerates that are modern plants and animals.

In the same fashion that cells differentiate into many different types, the human body as a whole is triggered by its chromosomes to specialise as one of two types, male or female. (Sometimes this goes wrong: the body gets mixed signals and you get intersex babies, or hermaphrodites.) In our evolutionary history this would have started as a much less pronounced difference between two groups in the one microscopic species. Importantly, they remained part of the same species because they exchanged genetic material directly, perhaps by simply pushing it through their cell walls. It immediately conferred an advantage in terms of survival and procreation because the DNA of every new offspring was a recombination of two sets instead of a clone of just one. More new combinations, more mutations and overall faster evolution. (This effect has been observed directly in adjacent populations of small fish, some of which reproduce heterosexually and some unisexually. The ones who have sex with each other build immunity to new diseases in fewer generations.) Once that was happening, the differences within the species were free to develop further, and a similar distinction was already present in every other species that descended from it.

Picking various amazing things about the body (or our planet, or the universe) and claiming they’re unachievable without a god is a terrible way to logically arrive at the necessity of a god, partly because of the argument from ignorance but mostly because there’s usually been a lot of work done to determine the method and it’s liable to be plonked in front of you. This approach is however an excellent way to reassure believers, who are less likely to research a claim that supports their beliefs, that they are justified in their faith. Consider the possibility that this is the spirit in which these ideas were conveyed to you, because they just plain don’t work on atheists.