Divine Command Theory says that right and wrong came about as a set of principles written on our soul by God telling us what is right and what is wrong. Gene Command Theory says that right and wrong came about as a set of principles written on our psyche by evolution telling us what is right and what is wrong.
Both theories are equally absurd, and they are absurd for the same reasons. Both fall victim to exactly the same objections.
On the theist side, we ask, "Is X good because it is loved by God, or is it loved by God because it is good?" If it is good because it is loved by God, then anything loved by God - no matter how horrendous - can be good. If God wants us to slaughter our neighbors and take their resources for our own, then the most virtuous among us are those who slaughter our neighbors and take their resources as our own. Yet, on the other hand, if God loves something because it is good, we are forced to conclude that the theist has not yet given us an answer to the question, "What is goodness?"
On the evolutionary ethicist side, we ask, "Is X good because it is loved by our genes, or is it loved by our genes because it is good?" If it is good because it is loved by our genes, then anything that comes to be loved by our genes is good. If our genes tell us to kill or to rape our step children, then the most virtuous among us are those who kill and rape our step children. Yet, on the other hand, evolution has selected particular ends because they are good, then this tells us that evolutionary theory has not yet given an answer to the question, "What is goodness?"
The reason both systems fall victim to the same objection is because they both commit the same mistake. They are both systems that allow agents to assign their sentiments to an external entity and then attach a special prescriptive force to that external entity.
The Euthyphro question used above exposes this sophistry. It asks those who make these arguments to justify assigning a special prescriptive force to this reservoir of the agent's own personal preferences to justify that assignment of special prescriptively. They both point out that this assignment of special prescriptively is unjustifiable.
And without it, divine command theory and gene command theory end up in the same dust bin.
These theories are probably embraced for the same reason. They give us a way to cloak our own desires and sentiments in an illusion of moral legitimacy. Both the divine command theorist and the evolutionary ethicist are actually seduced into a theory that says that they can take their own likes and dislikes and claim that they are moral laws by assigning them to a "greater power" - God or evolution, take your pick.
For many theists, God provides a legitimizing agent for doing what one pleases. One assigns one's sentiments to God and then, as if by magic, one is no longer acting so as to fulfill one's own desires. Now, one is acting to serve a 'higher purpose'. If anybody should be harmed in the process, they are not being harmed 'because it pleases me to do that which turned out to cause harm'. They were harmed 'in service to a higher purpose that justifies whatever sacrifices we may require of others'.
If we look at the way evolutionists face the subject of morality, they do the same thing. They take their own sentiments and they assign them to an 'evolved moral sense'. Then, as if by magic, one is no longer acting so as to fulfill one's own desires. One is now acting in service to moral principles refined through countless ages of natural selection. If anybody should be harmed in the process, then they are being harmed because we acquired desires to do things that tend to result in harm to others. They are being harmed because we are obeying a moral code written into our genes that gives us these moral commandments and justifies whatever harms may result.
Both views are equally mistaken. Yet, at the same time, both views are equally attractive because of their usefulness. However, the fact that these inferences get agents to the desired conclusions blinds the agents to the fact that they have thrown logic out the window. The goal, after all, is to coat acts grounded on personal preferences in an illusion of legitimacy. "God told me to do it," and "Evolution told me to do it," both serve that end quite efficiently. They both absolve the agent of personal responsibility and places the responsibility on an outside entity – something that the person making the statement can call a ‘higher purpose’.
As a result, evolutionary studies has now given us the cult of the evolved moral trait.
Over and over again, I see atheists embarrass themselves when confronting theists on matters of morality. When atheists reach to evolution to explain morality, they make logical leaps so broad and unfounded that they are not difficult at all for the theist to notice. The atheist does not notice them because he does not want to see them - in exactly the same way that theists blind themselves to the flaws in their own religion.
However, each can see the flaws that the other makes clearly enough. Each openly mocks the other for those mistakes, and the other dismisses the mocking as unfounded.
I want to take a moment to stress this fact. Many atheists openly mock and ridicule theists who brush aside objections to their view. PZ Myers is one of them. Yet, evolutionary ethicists brush aside the very same question. This is not an example where, "Here is something that evolutionary ethicists do that is similar to what they accuse theists of doing." This is a case of evolutionary ethicists doing exactly the same thing as they ridicule and mock others for doing.
There is no evolved moral sense, just as there is no God. The 'gene command theory' is just as absurd as 'divine command theory' and falls victim to exactly the same objections. The sooner that atheists recognize this fact the sooner they can stop appearing as nonsensical moral idiots in front of theists.