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[–][deleted] 7 insightful - 1 fun7 insightful - 0 fun8 insightful - 1 fun -  (3 children)

Because males are the default "template"

There is no biological basis to support this claim. Many biologists believe female is the default, but some believe there isnt any default sex at all. There is literally zero scientific literature making the claim that male is the default sex

https://www.frontiersin.org/articles/10.3389/fpls.2020.01162/full

https://pubmed.ncbi.nlm.nih.gov/4470128/#:~:text=Geneticists%20have%20discovered%20that%20all,maternal%20estrogens%20and%20maleness%20develops.

https://www.ncbi.nlm.nih.gov/books/NBK222286/

https://geneticliteracyproject.org/2017/09/21/embryos-arent-female-default-study-shows/

[–]proc0 2 insightful - 1 fun2 insightful - 0 fun3 insightful - 1 fun -  (2 children)

I'm talking about something different. At the genetic level it may be the case the fetus starts as female, but that doesn't say anything about the target morphology of the adult version of the fetus. Human females are not just smaller, they have a different morphology. This gap is relatively recent in evolutionary timelines for humans.

From this perspective it's not hard to see nature went from masculine to feminine, even in males, but much more so in females. No other female in the mammalian kingdom has enlarged breasts all the time, and more fat to accentuate form over function.

Even if we analyze at the superficial level, boys and girls are morphologically similar, and then it's girls that change into a different form, while boys just grow larger and that's about it.

[–]MarkTwainiac 3 insightful - 1 fun3 insightful - 0 fun4 insightful - 1 fun -  (1 child)

At the genetic level it may be the case the fetus starts as female, but that doesn't say anything about the target morphology of the adult version of the fetus. Human females are not just smaller, they have a different morphology. This gap is relatively recent in evolutionary timelines for humans.

When you say that in humans "the fetus starts as female," I think you mean embryo. A human embryo becomes a fetus at the time that gonadal differentiation occurs, which happens at 7-8 weeks.

Fetuses by definition will have male gonads, testes, or female gonads, ovaries. So the idea that in humans "the fetus starts as female" is nonsensical.

Also, your claim that "at the genetic level the fetus starts as female" gives the impression that during gestation in utero humans change DNA and sex chromosomes. This is not true. A human being's chromosomal sex, genetic sex and genetic profile is determined at conception. Some di novo mutations can occur when the first cells divide in the hours after sperm and egg merge and the blastocyst is forming, but the genetic sex of humans is set in stone from the get-go. It does not change as the blastocyst becomes an embryo, as the embryo grows into a fetus at week 7-8, or as the fetus develops from week 8 through 40.

It's not true that human embryos and their precursors, blastocysts, "start as female" either. Human embryos appear sexually undifferentiated when observed visually from the outside because they have not yet developed male or female gonads or the other urogenital and reproductive organs that are obvious to the eye. A male embryo who that not yet grown testes, penis, scrotum, prostate, vas deferens etc is NOT female; the embryo is merely an undeveloped male, or a male in primordial form.

When the cells of human embryos and blastocysts are examined with microscopes and other technologies that allow for a more accurate picture of what's happening, physical sex differences can be seen. In fact, marked physical sex differences in the cells of human blastocysts have been found just days after fertilization, at the time when the blastocyst is implanting in the uterine wall and begins to grow a placenta.

For the record: whether human fetuses have male or female external genitalia can be ascertained with 100% accuracy by sonograms taken from the exterior of pregnant women's abdomens at 14 weeks. Since full term pregnancy is 40 weeks, this means that the gonadal and genital sex of fetuses is easily discernible for the vast majority of the time that a fetus is a fetus.

Moreover, the genetic sex of human fetuses can be determined with 100% accuracy by testing a pregnant woman's blood drawn from the arm or finger in the standard way at 8-9 weeks of pregnancy; this common test is called the NIPT. The sex of a fetus can also be ascertained at 8-9 weeks of pregnancy by testing a tiny piece of the placenta taken in the invasive procedure called CVS (chorionic villi sampling). CVS has been in use since the mid-late 1980s; I personally had it when pregnancy more than 30 years ago.

[–]proc0 2 insightful - 1 fun2 insightful - 0 fun3 insightful - 1 fun -  (0 children)

Sure, it's the embryo. My point is focusing on traits that are expressed later with maturity. The evidence is in how humans look and have looked in the past millions of years and how that evolved over time. If the physical difference appear even earlier, then that's even more evidence.