- many things in our anatomy do not fit to our life circumstances
- genders converge to each other → differences no longer necessary
Overview of topics:
We have an idea why two sexes have prevailed in humans. Based on the different reproductive functions that already existed, a further specialization of the sexes just developed. Let’s now explore to what extent we can explain differences in body hair, nose size and muscle mass from this evolutionary perspective.
Anatomical differences between the sexes
Same and different
In many species we can hardly distinguish between female and male from each other based on their looks. Dogs and cats, for example, do not immediately show their sex. In many bird species the female is rather practically built and the male is equipped with eye-catching features. We know that this otherness of the male serves to impress the female. So, the art of impressing has been laid down optically. Thus the lion’s mane, tusks, antlers and the colourful appearance of some male chicken birds have one purpose: to demonstrate size, strength and presence. Even if the differences between the individual birds may remain veiled to the untrained human eye, a female of the species reads the quality of the genes from the jewellery.
There is an interesting connection across all species. When females and males look alike, they usually share the breeding of their offspring (symmetrical is the parental investment) and live in monogamous, faithful relationships. When the sexes live in long-term relationships, competition is almost removed from the equation and males do not need jewellery to convince females of themselves. Conversely, the greater the optical differences of the sexes, the shorter the relationship between them. Males need to impress females all the time, so they better get their looks right.
Females among mammals invest a lot of time per single offspring. Therefore, they have limited capacity of possible descendants and they need to maximize the chances of survival per offspring through excellent brood care. Such motivation has been anatomically deposited by mammary glands. (Interesting: nipples in men are probably only a remnant, because foetuses are initially always female).
As soon as the offspring is there, the female gives milk. It stand to reason that she will also take care of further care. In society mothers took over tasks that were compatible with their role as carers.
Anatomical peculiarities of women have in all probability developed in favor of the fulfillment of their tasks over millions of years. So, female hip basins are wider than shoulders, which facilitates pregnancy. There is also the reason why women walk the way they do and why walking downhill is more difficult for them. Women also develop more fatty tissue1.
As the survival of the offspring did not depend on males, they were able to take over tasks with a higher risk. And because they did not care for the offspring, they could also be away for longer periods of time and cover greater distances.
In Europe, the bones of men are on average 7 to 8 percent longer than those of women, which causes men to be taller and have longer limbs and is helpful for throwing and fast locomotion. They also have a stronger muscle profile. Men have an average muscle mass of 77 pounds compared to 51 pounds for women. Their better metabolism simplifies sustained muscle performance and allows sore muscles to disappear more quickly. With a higher volume and capacity of heart and lungs, men are better equipped for strength and fast movement. Blood pressure is higher on average and their metabolism is more intensive and thus better designed for sustained physical exertion.
The human brain weighs about 1400 grams. On average, a male brain weighs 100 grams more than a female brain. If you take a closer look at some areas, you can also see that in female brains the hippocampus is on average slightly larger compared to the brain as a whole and in men this is the case with the amygdala2. These mean differences are minimal and it is not possible to tell whether a brain is that of a woman or a man.
🤷 Evolutionary Remains 🤦♀️
This is our top 4 of evolutionary remains without function today:
1. Many people have no place in their jaws for the wisdom teeth. But what even causes problems today made sense once. When poor mankind did not know how to brush teeth, a few extra teeth were still very helpful.
2. We still have the equipment for it, but the third eyelid is missing in humans. It was an additional transparent protection of the eye, as it still occurs with different bird species.
3. The coccyx, which used to be different vertebrae, is a rudimentary remnant of a tail.
4. Goose bumps look ridiculous. The small muscle under the skin made much more sense when it brought a whole coat to a stand and thus made its owners look bigger and donated warmth.
It seems quite random in our society that men can on average and in some areas perform better sporting performances than women and that only women can breastfeed naturally. That looked different at a time when only those survived who were able to divide tasks optimally.
Evolution has a good laugh watching human beings forcing dogs into suits with ties and then laughing about it – after all, they had just done the same thing with himself. Evolution has no reason to believe that we can hold constitutional states and conduct disputes diplomatically. We do not even want to start with digitization. Evolution stays up to date, but it does not throw around with selection.
However, the differences between men and women seem to have been decreasing for a few millennia, as we can see from brain size and body hair. We have earned all the freedoms of the world. Household management is no longer a life’s work thanks to washing machines and supermarkets, and even mummy is no longer indispensable for breastfeeding. We have institutionalized protection through a constitutional state in which injustice is punished and institutions such as the military and police. We also have safe houses and, if necessary, surveillance cameras.
The question is whether we can use the freedom we have gained or whether we feel insecure because of the lack of predetermined roles for which our body is still equipped.
Genetic differences between the sexes
Evolution deals with the changes in genes within a species over many generations.
How genes prevailed
Now let’s take a look at it from the other side. What exactly do we mean when we say something “prevailed”? It is not the case that nature sets minimum requirements, and only those who meet them survive and pass on their genes. If, for example, nature would say that only individuals without bad breath can reproduce and all others not, our species would have found an abrupt end, because in the pre-toothpaste era there probably was no one without bad breath.
Let’s do this differently. We hypothesize that males with less bad breath had more success with the ladies (also the other way around). The decisive factor would then not be my individual bad breath value, but my breath situation compared to others. If males with less bad breath had more reproductive success than males with stronger bad breath, in the next generation the “gene for less bad breath” can be found in a significantly larger proportion of individuals. Bad breath we would call then a selection characteristic.
If a hereditary disposition favours characteristics that increase reproductive success (e.g. no bad breath), this hereditary disposition is more likely to be passed on and occurs proportionately more frequently in subsequent generations.
The genetic sex
You probably know the sex chromosomes:
XX – female
XY – male
When the germ cell is formed, the set of chromosomes is halved. The egg cell is always of type X, the sperm cell can be X or Y and is decisive for the sex of the baby (X – it´s a girl, Y – it´s a boy).
We are also familiar with the following developments:
X only → Turner syndrome
XXY or XXX → as long as a Y is in there, the development goes into the male direction, otherwise in the female direction
With the double X, female fetuses have a “spare tire” in case something doesn’t work. Male fetuses lack this. They have to live with what the X chromosome has to offer. On the quite large X chromosome lie “many enzymes and structural proteins anchored as genetic sequences”2. From this follows that extremes are rarer in women. Men have a much wider range in characteristics such as intelligence3. Both extreme giftedness and underachievement tend to occur in men.
» next topic:
The anatomical differences of the sexes were not new to you. But what about hormones – do you know the gender differences and what they were good for? Find out now »