Darwin vs. Lamarck

What is a theory? An explanation of some aspect of the natural world based on the best available evidence Summarizes hypotheses that have been well tested & are well supported A scientific theory is NOT just a guess – it’s well tested & accepted as true!

Populations of Species Species: a group of 1 type of organisms that interbreed & are reproductively isolated Population: a group of a particular species living in a certain area Whitetail Deer Whitetail Deer in the Texas Hill Country

Evolution Slow, gradual change in a population over time… … a looooooooooong time! Today, there are 14 species of finch that inhabit the Galapagos Islands. These 14 species evolved from a single ancestor that lived 2-3 million years ago.

The Theory of Evolution In the 1800s, many scientists agreed that life on Earth had changed (& still is changing). – Jean Baptiste Lamarck & Charles Darwin were 2 of the most important evolutionary scientists. Darwin & Lamarck agreed that evolution was occurring – the question was HOW? HOW do populations of species change over time?

Lamarck’s Theory on Evolution (1800s) Law of Use & Disuse: body parts got stronger or deteriorated depending on whether it was used or not Inheritance of Acquired Characteristics: acquired changes were passed on to offspring You’re naturally skinny, but you lift weights & become a body builder. Your children are born with HUGE muscles!

Lamarck’s Hypothesis Bird ancestors wanted to fly, so they tried until wings developed. Those that grew wings had offspring that were born with wings.

Millions of years ago, the ancestors of the modern giraffe had short necks. So, how do we explain the evolution of the long neck?

According to Lamarck… Giraffes’ necks grew longer from stretching for food. The acquired trait (long necks) was passed down to offspring. The giraffe population became long-necked.

What are your thoughts on Lamarck’s hypothesis?

Lamarck’s Hypothesis The clipped ears & tails of dogs could be passed on to offspring. ?????

Lamarck’s Hypothesis Let’s say you have your ears pierced. Were you born with this trait? NO – this is an acquired trait. According to Lamarck’s hypothesis, your baby would be born with pierced ears!

Lamarck’s Mistakes Was he correct? NO! Traits are passed down from parent to offspring by genes, NOT by an individual’s life experiences or activities. Lamarck did not know that traits were inherited through genes!

So, HOW is life evolving?

Charles Darwin Voyaged the world from During his travels, Darwin collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

Darwin’s Observations Food & resources are limited, so organisms have to compete to get them. Species produce too many offspring & not all will survive. Lions fight for food, space, mates, etc. Only about 1 in 8 male lions survive to adulthood.

Darwin’s Theory Survival of the fittest – or NATURAL SELECTION Only the best adapted (fittest) will survive! Adaptations come from your genes – you are born with them.

So, how did the long neck evolve?

According to Darwin… Some giraffes had short necks, but a few giraffes were born with a random mutation that gave them long necks. Neck length is determined by genes. Giraffes cannot change their genes by stretching their necks to make them grow. You are born with the genes you inherited!

According to Darwin… The short-necked giraffes had less food to eat, so they did not survive. The long-necked giraffes survived & reproduced & passed on the “good” genes.

Over time, what do you think happens to the short neck gene? The long neck gene? What will this giraffe population look like after several generations?

What are your thoughts on Darwin’s theory?

How does natural selection occur? Variation exists among individuals in a population. Some elephants are born with longer tusks than others. This variation gives some elephants a higher chance of survival. Elephants with large tusks are likely to be killed by poachers.

The elephants with the best genes will survive better & reproduce (high fitness). Which elephants have the higher fitness? How do you think elephant populations are changing?

Peppered Moths During the Industrial Revolution BEFOREAFTER