This is a long chapter and different from the other chapters. If you’re willing to read on, here are four quick and basic examples of how natural selection works. Otherwise, jump to the next chapter, ‘How Did Happiness Evolve?‘
(1) Faeces smell bad because we evolved to perceive them that way. If our early ancestors had found the smell and taste of faeces enjoyable, or even neutral, then in times of famine they would have eaten their faeces. Or eaten someone else’s. That would have been bad for their health, and they may even have died. Only the ones who found the smell and taste awful would have refrained from eating faeces, and they got to live long enough to mate and pass on their genes.
(2) Camels store fat in their humps and that fat provides them with energy when there isn’t food around. Let’s say millions of years ago a camel is born with genes giving it a bigger hump than most other camels. In a severe drought that camel, having a larger energy supply on its back when food is scarce, is more likely to survive and pass on its genes. Over millions of years, with similar situations occurring, all camels end up with the gene and bigger humps. Natural selection has ‘guided’ a physical change.
(3) Let’s say millions of years ago there lived an animal similar to today’s okapi. On one side of a mountain range there are the open spaces of savannah, and the creatures fight with their heads to win mates. The ones that happen to born with bigger necks will have an advantage, and get to pass on their genes.
On the other side of the mountain is jungle, and if one of those creatures is born with a bigger neck it will have no advantage. It might well injure itself swinging its head.
Over millions of years, in those different conditions, the two groups of creatures will develop so many differences that if you were to bring them together and mate them, they could not produce fertile offspring. They would have become separate species. (Robert E Simmons and Lue Scheepers, National Geographic Jan 15, 2013)
This may have happened. The giraffe’s closest extant (living) relative is the okapi, which lives in the Congo rainforest. It has a short neck.
There are other theories about why giraffes might have long necks: it might be that the tallest giraffes could reach leaves other giraffes couldn’t, and that would have helped them in times of famine. Or, the tallest giraffes were better able to scan the landscape for predators.
(4) A monkey born with the propensity to break nuts and eat the kernels has an abundant food source, and is more likely to survive a drought. Over time, all its descendants will have the propensity to break nuts and eat the kernels. Natural selection has ‘guided’ a behavioural change.
So, although gene mutations are random, over generations the mutations beneficial to the species can become normal to the species. That’s the process of natural selection. It is generally thought that most physical features and behavioural traits of organisms have come about in this way.
If a zebra were to be born with genes giving it an extra leg it would have trouble running fast, and it would easily be caught by a predator. So, it would not live long enough to pass on its genes. Therefore, we won’t see zebras walking around with five legs.
How do new species come into being?
There are different ways to establish a species and it’s not clear cut. We like putting animals into clear categories, like stamp collectors do with their stamps, but evolution has its own rules, and likes to break them. So, we often end up deciding on a new species based on our rules. A species exists if we say it does.
Here are four ways we determine a species:
(1) If two animals mate but cannot produce fertile offspring, they’re different species.
For example, if you mate a female horse (mare) with a male donkey (jack) they’ll produce a mule, and if you mate a female donkey (jenny or jennet) with a stallion they’ll produce a hinny. But neither mule nor hinny will be fertile. Therefore, donkeys and horses are different species.
‘Natural selection penalises mating with the wrong species, especially where the species are close enough for it to be a temptation, and close enough for hybrid offspring to survive, to consume costly parental resources, and then turn out to be sterile, like mules.’
‘The Ancestor’s Tale’ by Richard Dawkins and Yan Wong. P389.
(2) When animals could mate and produce fertile offspring, but don’t, they’re different species. For example,
(i) there are frogs that mate only in the morning. They share a waterhole with identical frogs that mate only in the evening. Because those two groups don’t mate, they’re different species.
(ii) Two birds might have the capacity to successfully mate, but if their courtship procedures are not aligned, they won’t mate. They will be deemed to be different species.
(iii) In Africa, red cichlid fish could mate with blue cichlid fish and produce fertile offspring, but they don’t mate. That makes them different species.
What makes the red cichlid fish different from the blue cichlid fish in the first place? In the book, ‘The Ancestor’s Tale’, it is suggested that if cichlids are separated for a while – for example, if they live and breed in separate reefs for many generations – they can, through random mutations, develop differences like colouring. If that difference in colour is enough to prevent the red and blue cichlid fish from mating when they do happen to meet, that’s enough to make them two species.
Over time, the genetic differences between the two groups of fish, or frogs, would eventually widen to the point where even if they mated they would be unable to produce fertile offspring.
(3) When the animals are obviously different from one another, even though they could mate and produce fertile offspring.
(i) For example, polar bears and American brown bears have different physical characteristics, behaviours and temperaments, so they are considered to be different species even though they can successfully interbreed, and are doing so.
(ii) Then we have the Hooded crow and Carrion crow. They look different from each other and mate in their own groups, but where their territory intersects they mate successfully with one another and produce fertile hybrids.
(iii) In the U.S. Coyotes and wolves are interbreeding and producing fertile offspring called ‘coywolves’.
(iv) Homo sapiens and Homo Neanderthalensis were two species that looked different, but before we killed off the Neanderthals some of us mated successfully with them, and produced fertile offspring. That’s why about 20% of us have within us a small percentage of Neanderthal DNA.
The trouble with this method of determining a species is that there are many exceptions: there are animals that look different from one another, but they are the same species. For example, in the case of the Hawaiian happy-face spider (Theridion grallator), both sexes come in countless colours, but they all interbreed, so they’re the same species. Dogs, obviously, can look very different from one another, but they’re the same species. Humans today vary significantly in colour and shape, but of course, we’re the same species.
(4) DNA. We used to think there was one species of giraffe, but according to the October 2019 edition of The National Geographic magazine: “new DNA research has identified four distinct species.” (The Northern giraffe, the reticulated giraffe, the Masai giraffe and the Southern giraffe. There are sub species too.)
Are lizards related to giraffes?
Yep. Their common ancestor goes back more than a hundred million years.
‘An eel-like creature from 505 million years ago was a forerunner to all vertebrates, from fish to humans. Fossil evidence confirms that Pikaia gracelens had a rod of elastic tissue running along its back, making it the oldest chordate ever found.’
New Scientist, 10 March 2012.
Did humans evolve from gorillas, chimpanzees or monkeys?
From none of those animals, though we share with those primates a common ancestor that existed more than sixty million years ago. It probably looked something like a nimble rodent. Over a long time, over large areas, and in varying conditions, those ‘nimble rodents’ evolved into different animals, depending on the environmental forces. A simple and speculative example: if the rodent-like animals lived in rainforests that offered abundant food in the trees, they would probably stay in the trees, and over millions of years become monkeys or tree-dwelling apes.
Let’s say another population of the same rodent-like animal lived on savannah plains, and found food in the long grass. The ones born with a mutation allowing them to stand on two legs and see above the grass would have had a significant advantage, and be more likely to survive and produce offspring. Over millions of years they might evolve into bipedal, land dwelling apes.
Susannah Thorpe and her colleagues of The University of Birmingham suggest another possibility: that our ancestors evolved to stand on two legs while still in the trees. Balancing on two feet and using their hands to hold branches for balance helped them reach the fruit on small, outlying branches (New Scientist, 9 June 2007).
Yet another theory suggests we became bipedal from wading in water. The ones able to stand upright could carry their infants while plucking nutritious weeds. Plus, they could find food in deeper water than could a non-bipedal ape.*
In pages 112 to 115 of their book, Dawkins and Wong mention anthropologist Owen Lovejoy, who suggested that by standing on two legs, the apes’ hands were freed, and that enabled them to carry infants or carry food. That ability conferred upon them a significant survival advantage.
Jonathan Kingdon’s book, ‘Lowly Origin’, gets a mention too. Kingdon has a ‘squat theory’. By being able to squat, the apes could turn over rocks or leaf litter to find insects, worms, snails and other nutritious morsels.
And, on page 322, Richard Dawkins and Yan Wong themselves suggest the possibility that one particular ape made a habit of standing on its hind legs, and as a result enhanced its sexual attractiveness and social status. The gimmick became fashionable with others following suit, and the ones that managed to maintain their posture mated often and passed on their genes.
What other factors would have made us human?
Over time we evolved other ‘game changers’: we evolved vocal cords that allowed complex language, and it has been suggested that we gained a larger brain (with commensurate intelligence) at the expense of our muscle strength and body hair.
What is a subspecies?
Imagine a thousand giraffes on a large island in a river, and they become isolated when the river fills with crocodiles. Over a long period of time those island giraffes develop their own characteristics, such as different markings or shorter necks. If they were transported to the mainland and could still successfully breed with the mainland giraffes, the two groups would be the same species. However, because of their different characteristics the island giraffes, the minority, would be labeled a subspecies.
As explained above, scientists used to think there were sub species of giraffes, until DNA evidence determined that they were separate species.
Can evolution explain the origin of life?
No, and it’s not meant to. Creationists often try to disprove evolution by pointing to the fact that we don’t know how life came into being. However, the origin of life has nothing to do with evolution. It’s a different topic entirely.
Are there other factors contributing towards evolution?
(1) One factor is epigenetics. That’s when genes are influenced by the environment. For example, a creature living in drought conditions, unable to feed itself properly, might give birth to young smaller than normal. The drought might then break, and the young would grow up in much better conditions. However, when it’s their time to give birth they might also give birth to young that are smaller than normal. Had the drought not ended, then giving birth to smaller young might be an advantage for those young – they would need less food to stay alive.
Another example: a creature living an abnormally stressful life might give birth to young that grow up more prone to becoming stressed than they otherwise would be, and when they give birth, their young might be born with genes switched on ready to make them stressed, even in mild circumstances. That’s epigenetics.
(2) Some viruses can also contribute towards a creature’s evolution by infecting its sperm or egg, thereby changing the creature’s DNA slightly. Those changes would be inherited by its young, and if those changes are beneficial they will be passed on to future generations. For example, primates like chimpanzees, gorillas and we humans have within us ancient virus DNA that helps our females give birth to healthy young.
What does the process of natural selection have to do with core happiness?
See you in the next chapter!
* That ‘Aquatic Ape’ theory was put forth by Alister Hardy and championed by Elain Morgan, according to Richard Dawkins and Yan Wong in their book, ‘The Ancestor’s Tale. (The Ancestor’s Tale, A Pilgrimage to the Dawn of Life. Richard Dawkins and Yan Wong. Weidenfeld & Nicolson 2016)