Evolution

pteradactyl                          

First Mammals -- A tiny shrew survives among the dinosaurs




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A Godless Philosophy - Contents

Preface  (What's this all about?)

The Story of Evolution

14,000,000,000 y.a. -- The Big Bang
Evolution begins

4,600,000,000 y.a. -- Our Sun and Earth
Stars evolve, producing the complex elements of organic life

2,500,000,000 y.a. -- First life forms on Earth
A bacteria reproduces itself, and the race is on

220,000,000 y.a. -- First mammals
A tiny shrew survives among the dinosaurs

30,000,000 y.a. -- The great apes of Africa
Chimps achieve sociability, planned combat, and use of natural objects as tools

5,000,000 y.a. -- Earliest human ancestors
It looks like a chimp but walks upright

3,000,000 y.a. -- Earliest toolmakers
Still chimp-like, this larger-brained ape makes the first stone tools

1,800,000 y.a. -- Later pre-humans
More human-looking without fur, this naked ape conquers fire and reaches Eurasia   

300,000 y.a. -- Neanderthals
Evolved in Europe's Ice Age, they hunt and kill 7-ton mammoths

50,000 y.a. -- Modern humans (Homo sapiens)
Fully human now, we narrowly escape extinction to follow our destiny

45,000 y.a. -- Spread of modern humans throughout Eurasia
Out of Africa, we encounter the pre-humans and fight our way north

30,000 y.a. -- Extinction of the last pre-humans
Neanderthals, the tough guys, hold out the longest

15,000 y.a. -- First settlements, city-states and empires
It takes us 35,000 years to create the first small city

600 y.a. -- Racial differences and European conquests
Guns, germs and steel

Now -- Human evolution in modern times
Where are we, and what lies ahead?

Theory or Science?  Sources and References


Evolution's Implications  (Summary)


Miscellaneous Musings



Fossil evidence dates the earliest known mammals to 220 million years ago. However, our direct ancestors, mammals that give birth to live young, came later. Scientists have recently discovered a 125-million-year-old, well-preserved fossil of a tiny shrew-like species that scurried about in bushes and the low branches of trees.

They lived in the age of dinosaurs, a hazardous time for small furry creatures. Yet our ancient shrewish ancestor proved more successful than the dinosaurs in the game of evolution. Quite prolific, in fact, begetting thousands of descendant mammal species, including us humans.

But we've jumped all the way from bacteria to a warm-blooded animal. Before we go further, let's review how the game of biological evolution is played.

Most people think evolution means "survival of the fittest." While that does match the image of a small rodent escaping a velociraptor, it omits the key mechanism behind evolution. Yes, the shrew must survive in order to stay in the game. And shrews as a species must have been able to survive major catastrophes (e.g., the one that wiped out the dinosaurs). However, for that one little escape artist to advance in the game of evolution, his or her genes must wind up in the next generation of shrews more prolifically than those of the average shrew.

For a population to evolve, some lasting change must occur in its gene pool. Any such change, of course, has to originate with one or more members of the population, whose individual genetic codes are constantly in flux. These individual genetic variations are generated occasionally by mutations and ceaselessly by the every-generation shuffling of male and female genes in every offspring.

Most genetic variations which differ from the norm ultimately get shuffled out of the deck. As we learned in Biology 101, only half of the male's genes and half of the female's genes wind up in each offspring; the rest are discarded. So unless a given genetic variation favors more offspring, it gets lost within a dozen or so generations. If it is favorable, it tends to propagate throughout the population.

But how is "favorable" decided? Here is where natural selection comes in, rejecting changes for the worse and retaining those that confer "reproductive advantage" (resulting in more offspring). For example, an increase in size would not have helped shrews in an environment full of hungry velociraptors. But a variation in forelegs which aided fast digging would have propagated throughout the shrew population.

While natural selection is the primary force in evolution, "sexual selection" is also at play, sometimes yielding a reproductive advantage which has nothing to do with fitness or survivability. Darwin observed this, noted it, and then soft-pedaled it in the face of a prudish Victorian reaction. After a century of being considered controversial, sexual selection has recently been acknowledged as an important force in evolution.

For example, let's say that our shrew isn't such a great escape artist but manages to survive anyway, and happens to have a less furry tail than the other guys. And let's say that the girl shrews just happen to get a warm feeling at the sight of an almost-naked male tail -- so much so that they always sidle up to our shrew first when they're fertile. Many generations later, all shrews could wind up with totally naked tails, without any push at all from natural selection.

Sexual selection accounts for a male lion's mane and a peacock's tail feathers, and it is a major reason for racial differences in humans today, as we'll explore later.

Although a mutation can cause an abrupt change, genetic variations produced in any one generation are normally small. Nevertheless, favorable differences accumulate, like compounding interest, with each generation. Over time, they can add up to major changes in the population's gene pool and ultimately culminate in new species.

That's how our ancient shrews evolved. And 100 million years later, one of their thousands of descendant species turned out to be chimpanzees...


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Copyright © 2011 Marshall C. Whitfield