This is really just a question for anyone who believes in abiogenesis (obviously including guided by God).
My husband wants to know how two sexes for reproduction are supposed to have developed via cell by cell progression, and how two different bodies started to form simultaneously for those animal groups. Can any theistic evolutionists explain? Is there an improved chance of survival involved?
Thank you in advance for any replies.
To understand evolution, you have to gain an understanding of deep time. There are a few complications in your question.
For starters, abiogenesis has to do with the origins of life. Evolution has to do with the descent with modification of life, after it already exists.
Abiogenesis - Wikipedia
Evolution - Wikipedia
So your initial sentence says:
"
This is really just a question for anyone who believes in abiogenesis (obviously including guided by God)."
Which could be rephrased as:
"This is really just a question for anyone who believes that life came from non life"
But whether you're a theistic evolutionists or a Creationist, all of us believe that life came from non life, be it God's dust or molecules of a primordial soup.
With that said, we can now move on to your question.
"
My husband wants to know how two sexes for reproduction are supposed to have developed via cell by cell progression, and how two different bodies started to form simultaneously for those animal groups. "
So you're asking how two sexes formed and how two different bodies formed simultaneously for "those animals".
You should understand that every animal that we have ever known to exist, post-dates the existance of sexual reproduction by hundreds or even thousands of millions of years (or 1.5 thousand-million or 1.5 billion). Studies in genetics estimate the evolution of sexual reproduction some 2 billion years ago, while the fossil succession pins the appearance of animals sometime shortly before the Cambrian explosion and somewhat earlier than the ediacaran biota 800-700 million years ago.
So, what I am pointing out is that animals didn't exist when the evolution of sex first occurred. Sex pre-dates animals by a very long time. With this, the words "body" and "animal" are strange words to use in regards to the origin of sex because animals and bodies didn't yet exist.
So back to your question:
"
My husband wants to know how two sexes for reproduction are supposed to have developed via cell by cell progression, and how two different bodies started to form "
It should also be noted that the origins of sex do not need two different "sexes" or genders. Sex or sexual reproduction, in it's most primitive form, involves two organisms joining together, combining/mixing genes and in some fashion, reproducing or separating. This can actually occur with just a single sex/gender and has been recorded to exist in single celled eukaryotes.
So the answer to the question, in a very simple response, is that sex came about when life still existed as eukaryotic cells, that simply combined, transferred genes, and separated. Before there even was a true male and female.
Bodies would otherwise form just as they do in any other scenario, through selective pressures. If one organism has some means of connecting and swapping genes that doesn't work properly in combination with others, they don't reproduce and they go extinct. Whereas organisms with an efficient means of connecting with others, have more offspring. Genders take form as selective pressures drive mutations that produce sexual dimorphism and then further propel it in ways to produce new body designs, such as described in the papers below.
https://royalsocietypublishing.org/doi/10.1098/rspb.2010.2220
The Evolution of Sexual Dimorphism: Understanding Mechanisms of Sexual Shape Differences | IntechOpen
The easiest way to understand evolution is to start with the present day and work your way backwards. So I would recommend first understanding the geologic column and fossil succession, along with basic concepts of biology such as mutation and descent with modification, then work your way backwards through time. As opposed to starting in the beginning, which is far more complex, and working your way forward through time.
It's like asking questions about big bang physics when all you really need to understand evolution is to pull out a telescope.
This also reminds me a bit of the chicken and the egg question. The answer begins with understanding that neither male nor female (as we know them) nor chicken egg nor chicken, necessarily came first. Rather their origins came from a time in which chickens nor chicken eggs, and male nor female existed. And their existences came about, for practical purposes, simultaneously.
Although we could argue that the chicken egg came first, then the chicken. But the chicken egg would have to first come from a non-chicken. Though we could argue that the egg comes before the chicken because eggs predate chickens by millions of years...maybe a discussion for another day.
